Reports on Astronomy [1st ed.] 978-90-277-1423-7;978-94-009-7837-9

Table of contents :
Front Matter ....Pages i-viii
Ephemerrides (T. Lederle)....Pages 1-13
Documentation and Astronomical Data (W. D. Heintz)....Pages 15-18
Astronomical Telegrams (J. Hers, B. G. Marsden)....Pages 19-20
Mécanique Céleste (Y. Kozai)....Pages 21-32
Positional Astronomy (E. Høg)....Pages 33-42
Instruments and Techniques (Patrick A. Wayman)....Pages 43-54
Solar Activity (H. Yoshimura, R. Howard, M. Kopecký, H. Zirin, V. Bumba, O. Engvold et al.)....Pages 55-92
Radiation and Structure of the Solar Atmosphere (R. C. Willson, E. Fossat, R. W. Noyes, H. C. Spruit, E. R. Priest, E. Hildner et al.)....Pages 93-114
Atomic and Molecular Data (Données Atomiques et Moleculaires) (Patrick A. Wayman)....Pages 115-151
Physical Study of Comets, Minor Planets and Meteorites (F. L. Whipple, Z. Sekanina, E. Everhart, M. F. A’Hearn, M. Festou, E. Gerard et al.)....Pages 153-174
Physical Study of Planets and Satellites (V G Tejfel’, M E Davies, B A Smith)....Pages 175-179
Rotation of the Earth (B. Guinit, K. Yokoyama, G. A. Wilkins, P. Paquet)....Pages 181-194
Positions and Motions of Minor Planets, Comets and Satellites (Positions et Mouvements des Petites Planetes, des Cometes et des Satellites) (E. Roemer)....Pages 195-210
Light of the Night Sky (Lumiere du Ciel Nocturne) (H. Tanabe)....Pages 211-218
Meteors and Interplanetary Dust (Z. Ceplecha, C. S. L. Keay, Peter M. Millman, D. O. ReVelle, B. A. Lindblad, W. J. Baggaley et al.)....Pages 219-236
Photographic Astronomy (Heinrich Eichhorn)....Pages 237-240
Stellar Photometry and Polarimetry (M. S. Bessell, A. R. Hyland, J. A. Graham, J. Tinbergen, P. F. Chugainov, B. Hauck)....Pages 241-256
Double Stars (O. G. Franz)....Pages 257-262
Variable Stars (John R. Percy, B. Szeidl, Bruce C. Cogan, R. F. Wing, Arthur N. Cox, R. E. Gershberg et al.)....Pages 263-302
Galaxies (B. E. Westerlund, P. C. van der Kruit, P. W. Hodge, V. C. Rubin, E. A. Dibay, M. W. Feast et al.)....Pages 303-341
Stellar Spectra (Y. Andrillat, J. Jugaku, R. Viotti, M. F. McCarthy, K. O. Wright, C. Jashchek et al.)....Pages 343-360
Vitesses Radiales (M. Duflot)....Pages 361-368
Time (S. Iijima)....Pages 369-382
Structure and Dynamics of the Galactic System (G. G. Kuzmin)....Pages 383-412
Interstellar Matter and Planetary Nebulae (V. Radhakrishnan, J. Lequeux, U. Mebold, B. Zuckerman, B. Donn, B. G. Elmegreen et al.)....Pages 413-456
Stellar Constitution (R. J. Tayler, A. Maeder, J. Craig Wheeler, J. Cox, J. J. Monaghan, V. Castellani et al.)....Pages 457-478
Theory of Stellar Atmospheres (Thèorie Des Atmosphères Stellaires) (Patrick A. Wayman)....Pages 479-491
Star Clusters and Associations (B. Balázs, G. Harris, R. E. White, D. Heggie)....Pages 499-526
Exchange of Astronomers (Jean Delhaye)....Pages 527-528
Radio Astronomy (G. Swarup, R. Fanti, I. I. K. Pauliny-Toth, A. Bridle, K. I. Kellermann, G. K. Miley et al.)....Pages 529-549
History of Astronomy (M. A. Hoskin)....Pages 551-552
Close Binary Stars (G. Larsson-Leander, R. H. Koch, A. H. Batten, A. M. Cherepaschuk, Y. Kondo, D. M. Gibson et al.)....Pages 553-577
Commission de L’Astronomie a Partir de L’Espace (R. J. van Duinen, J. L. Steinberg, G. G. Fazio, Anne B. Underhill, Albert Boggess, M. Oda et al.)....Pages 579-619
Stellar Classification (R. F. Garrison, D. J. MacConnel, V. Straizys, P. C. Keenan, C. Jaschek, A. Slettebak)....Pages 621-632
Teaching of Astronomy (Patrick A. Wayman)....Pages 633-634
Cosmology (G. O. Abell)....Pages 635-648
High Energy Astrophysics (Patrick A. Wayman)....Pages 649-649
The Interplanetary Plasma and the Heliosphere (A. Z. Dolginov, S. Grzedzielski, F. Paresce)....Pages 651-665
Identification and Protection of Existing and Potential Observatory Sites (Patrick A. Wayman)....Pages 667-668
Back Matter ....Pages 669-669

Citation preview

TRANSACTIONS OF THE

INTERNATIONAL ASTRONOMICAL UNION VOLUME XVIIIA REPORTS

INTERNATIONAL COUNCIL OF SCIENTIFIC UNIONS

INTERNATIONAL ASTRONOMICAL UNION UNION ASTRONOMIQUE INTERNATIONALE

TRANSACTIONS OF THE

INTERNATIONAL ASTRONOMICAL UNION VOLUME XVIIIA

REPORTS ON

ASTRONOMY Edited by

PATRICK A. WAYMAN General Secretary of the Union

D. REIDEL PUBLISHING COMPANY DORDRECHT : HOLLAND / BOSTON: U.S.A. / LONDON: ENGLAND

Library of Congress Cataloging in Publication Data Main entry under title: Reports on astronomy. (Transactions of the International Astronomical Union; v. 18 A) English and French 1. Astronomy-Congresses. 1. Wayman, Patrick A. II. International Astronomical Union. III. Series. QB1.I6 vol. 18 A 520s [520] 82-3802 ISBN-13: 978-94-009-7839-3 001: 10.1007/978-94-009-7837-9

e-ISBN-13: 978-94-009-7837-9

Published on behalf of the International Astronomical Union by D. Reidel Publishing Company, P. 0. Box 17, 3300 AA Dordrecht, Holland

All Rights Reserved Copyright © 1982 by the International Astronomical Union Softcover reprint of the hardcover 1st edition 1982 Sold and distributed in the U.S.A. and Canada by Kluwer Boston, Inc., 190 Old Derby Street, Hingham, MA 02043, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, p. 0. Box 322, 3300 AH Dordrecht, Holland D. Reidel Publishing Company is a member of the Kluwer Group

No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any informational storage and retrieval system, without written permission from the publisher

PRE F ACE IAU Transactions are published as a volume corresponding to each General Assembly.

Volume A is produced prior to the Assembly and contains Reports on

Astronomy, prepared by each Commission President.

The intention is to summarize

the astronomical results that have affected the work of the Commission since the production of the previous Reports up to a time which is about one year prior to the General Assembly.

Volume B is produced after the Assembly and contains accounts

of Commission meetings which were held and other material. In 1976 (Grenoble), volume XVI, and 1979 (Nontreal), volume XVII, IAU Transactions A were produced in three parts, each of about 230 pages, so that individuals could choose to purchase part only of the complete volume. a different policy is adopted.

In 1982 for this volume

Volume XVIIIA reverts to one part, produced from

camera-ready manuscript, published in one cloth-bound edition, but there is the supplementary production of a paper-bound volume in which standards of production have been adopted that enable a fixed number to be produced for distribution at the 18th General Assembly at Patras, Greece, at a low cost if ordered on the Registration Form by participants.

In this way it becomes a working document of the General

Assembly as was the production of the "Draft Reports" of earlier General Assemblies. It receives the title "Reports on Astronomy, 1982 - 18th General Assembly of the IAU, Patras, Greece". The style and length of Presidents' Reports varies from 2-page outline summaries to, in one case, a 44-page compilation with ten named contributors, or in other cases many hundreds of references.

Nost of the Reports are in English and the Union

is indebted to those Presidents who use one of the official IAD languages for their Reports when it is not their mother tongue.

The technicalities of camera-ready copy

mean that a few typing errors that remain undetected could not be corrected in the time available.

Generally speaking, the production of the camera-ready copy by

Presidents was of a very high standard and thanks are due to all those, including the staff of the IAD Secretariat, who have used their skill to produce the material for this volume. Patrick A. Wayman General Secretary

CON TEN T S REPORTS OF COMMISSIONS Preface

v

4

Ephemerides

Ephemerides

5

Documentation and Astronomical Data

Documentation et Donnees Astronomiques

15

6

Astronomical Telegrams

Telegrammes Astronomiques

19

7

Celestial Mechanics

Mecanique Celeste

21

8

Positional Astronomy

Astronomie de Position

33

9

Instruments and Techniques

Instruments et Techniques

43

10

Solar Activity

Activite Solaire

55

12

Radiation and Structure of the Solar Atmosphere

Radiation et Structure de l'Atmosphere Solaire

93

14

Atomic and Molecular Data

Donnees Atomiques et Moleculaires

115

15

Physical Study of Comets, Minor Planets and Meteorites

Etude Physique des Cometes, des Petites Planetes et des Meteorites

153

16

Physical Study of Planets and Satellites

Etude Physique des Planetes et des Satellites

175

19

Rotation of the Earth

Rotation de la Terre

181

20

Positions and Motions of Minor Planets, Comets and Satellites

Positions et Mouvements des Petites Planetes, des Cometes et des Satellites

195

21

Light of the Night Sky

Lumiere du Ciel Nocturne

211

22

Meteors and Interplanetary Dust

Meteores et la Poussiere Interplanetaire

219

24

Photographic Astrometry

Astrometrie Photographique

237

25

Stellar Photometry and PolarimetrYPhotometrie et Polarimetrie Stellaires

241

26

Double Stars

Etoiles Doubles

257

27

Variable Stars

Etoiles Variables

263

28

Galaxies

Galaxies

303

29

Stellar Spectra

Spectres Stellaires

343

30

Radial Velocities

Vitesses Radiales

361

CONTENTS

viii

31

Time

L'Heure

369

33

Structure and Dynamics of the Galactic System

Structure et Dynamique du Systeme Galactique

383

34

Interstellar Matter and Planetary Nebulae

Matiere Interstellaire et Nebuleuses Planetaires

413

35

Stellar Constitution

Constitution des Etoiles

457

36

Theory of Stellar Atmospheres

Theorie des Atmospheres Stellaires

479

37

Star Clusters and Associations

Amas Stellaires et Associations

499

38

Exchange of Astronomers

Exchange des Astronomes

527

40

Radio Astronomy

Radio Astronomie

529

41

History of Astronomy

Histoire de l'Astronomie

551

42

Close Binary Stars

Etoiles Binaires Serrees

553

44

Astronomy from Space

L'Astronomie

45

Stellar Classification

Classification Stellaire

621

46

Teaching of Astronomy

Enseignement de l'Astronomie

633

47

Cosmology

Cosmologie

635

48

High Energy Astrophysics

Astrophysique de Grande Energie

649

49

The Interplanetary Plasma and the Heliosphere

Plasma Interplanetaire et 1 'Heliosphere

651

Identification and Protection of Existing and Potential Observatory Sites

Protection des Sites d'Observatoires Existants et Potentiels

50

Working Group for Planetary System Nomenclature

a partir

de l'Espace

579

667 Groupe de Travail sur la Nomenclature dl Systeme Planetaire

669

4. EPHEMERIDES

(~PHEMtRIDES)

PRESIDENT: A M Sinzi. VICE-PRESIDENT: T Lederle. ORGANIZING COMMITTEE: V K Abalakin, S Aoki, R L Duncombe, J H Lieske, B L Morando, A Orte, P K Seidelmann, G A Wilkins, B D Yallop.

I. INTRODUCTION

Because of unforeseen difficulties, Dr Sinzi, President of the Commission, was not able to prepare this Report. It was then too late for asking the Directors of the almanac offices and the other Members of the Commission for informations. This Report is therefore based on the material just available, and it must be apologized for some lack from which it necessarily suffers. If possible, any omitted facts which appear to be serious, may be included in the Report for the following triennium.

II. INTERNATIONAL AND NATIONAL EPHEMERIDES

We are still in a period of development, and the problems to be resolved during the next few years may be characterized as follows: (a) Basic Changes to be introduced by the new System of Constants, the improved fundamental catalogue, and the new theories on which the ephemerides are based. Difficulties will arise by the requirements of continuity and consistency and of best fitting the most recent observations. Compromises have to be searched in order to find optimal solutions. (b) Modifications in the presentation which result from re-considering the real needs of the users of the almanacs. In view of their different aspects some variety between the almanacs should be quite desirable. (c) Improvement of the content and rationalization in the production of the almanacs by making use of best computation facilities and modern printing techniques. The general aspects of these developments are described in detail by P K Seidelmann in (25.047.022). Some particular informations are given in the following survey. HM Nautical Almanac Office, Royal Greenwich Observatory, Herstmonceux, UK, and the Nautical Almanac Office, US Naval Observatory, Washington, USA, have continued to cooperate in the production and publication of three unified almanacs, namely the Astronomical Almanac (previously the Astronomical Ephemeris/American Ephemeris), the Nautical Almanac, and the Air Almanac, and of the Astronomical Phenomena. Data for other major almanacs and special purposes has been supplied on request. The almanacs for 1984 onwards will be based on new heliocentric ephemerides of the planets and of the Moon supplied by the US Naval Observatory; the geocentric ephemerides being prepared by HM Nautical Almanac Office will take into account the changes in the IAU system of astronomical constants adopted in 1976 and at subsequent meetings. The preparation of Planetary and Lunar Coordinates for 1984-2000 is in progress. The Almanac for Computers, published by the Nautical Almanac Office, Washington, annually since 1977, contains polynomial coefficients which provide the means for computing the positions of the Sun, Moon and planets to the accuracy desired for any time during the year. It also includes star coefficientsin order to provide mean or apparent places of stars to the desired levels of accuracy and also a list of useful formulas for performing special computations (G A Wilkins / P K Seidelmann).

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COMMISSION 4

During the period under review three issues of the Astronomical Almanac of the USSR for the years 1982, 1983, 1984 have been published by the Institute for Theoretical Astronomy, Leningrad, USSR, the fundamental ephemerides of the Sun, Moon, and major planets being computed on the classical theoretical basis. The ephemerides for physical observations of major planets for 1985 will be computed on the basis of the new values of the rotational elements and cartographic coordinates as it was recommended in the Report prepared by the IAU Joint Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites. The ephemeris of the lunar crater M6sting A, which is regularly published in the Astronomical Almanac of the USSR will be based from 1985 onwards on the new set of the Moon's physical libration parameters as given by K Koziel in 1964 and on the Moon's physical libration series defined by D H Eckhardt's theory in 1970 (V K Abalakin) . The Connaissance des Temps, which is published annually by the Bureau des Longitudes, Paris, France, uses developments of the coordinates into Chebychev polynomials. Bureau des Longitudes published also supplements to Connaissance des Temps for 1981 and 1982 giving the phenomena and configurations of the satellites of Jupiter and another supplement entitled "Ephemeris of the faint Satellites of Jupiter and Saturn for 1981, 1982, 1983" where the Chebychev polynomials developments of the coordinates of those bodies are given (B L Morando). L'Instituto y Observatorio de Marina, San Fernando, Espagne, a commence a faire une revision progressive dans Ie contenu des Efemerides Astron6micas. Cette revision est demaree avec Ie volume 1981 et doit etre finie avec celui du 1984 dans lequel les Recommendations UAI de Grenoble sur les Constantes Astronomiques, Equinoxes, etc., seront appliques. Etant donne Ie tirage limite de nos "Efemerides" et la variete du public auquel elles sont destinees, on a decide de ne pas faire des reformes radicales. On est arrive a conserver la meme disposition des differents tableaux, mais en eliminant certaines colonnes qu'on peut obtenir sans peine. Les coordonnees de la lune a, 0 et IT sont donnees journalierement sous la forme de coefficients de Tchebychev. La Explicaci6n qui apparait a la fin des "Efemerides" va etre simultanement racourcie et les concepts seront revises, bien dans la publication meme, ou bien dans une brochure a part, comme supplement dans certaines annees. On fait des efforts pour arriver a mecaniser Ie plus que possible Ie tirage des "Efemerides". Pour satisfaire certaines demandes on distribue aussi depuis 1979, une petite brochure a titre experimental nomme Almanaque Nautico Reducido pour les calculs du bord avec des petites calculatrices (A Orte). The Chinese Astronomical Ephemeris is published by the Academia Sinica, Purple Mountain Observatcry, Nanking, China, every year since 19~5. On the proposal by surveyors, the apparent positions of stars are given for UT at intervals of 10 days (N-y Li).

°

During the time period of this survey the Indian Ephemeris, prepared by the Positional Astronomy Centre, Calcutta, India, has been published for the years 1980, 1981 and 1982 (A Bandyopadhyay). The Japanese Ephemeris, the Nautical Almanac, the Abridged Nautical Almanac and the Polaris Almanac for Azimuth Determination have continued to be published by the Hydrographic Department of Japan, Tokyo, Japan. From the volume for 1980, the fundamental ephemerides of the Sun, the Moon and the planets in the Japanese Ephemeris are computed at the Department, being rigorously based on the respective basic data on which the Astronomical Ephemeris had been based. The Japanese Ephemeris for 1980 to 1982 contain predictions of the solar eclipses in 1981-1985, 19861990 and 1991-1995, respectively, as a supplement. This series will be concluded in the volume for 1983. Also, trigonometric series or basic values for approximate positions of the Sun, the Moon, the planets and some stars are supplemented to the Nautical Almanac and the Abridged Nautical Almanac since the volume for 1978, together with a series of formulae for obtaining the apparent places (S Aoki) .

EPHEMERIDES

3

In the preparation of the annual volumes of the Apparent Places of Fundamental Stars from 1981 onwards, the Astronomisches Rechen-Institut, Heidelberg, F. R. Germany, has transcribed the computed data on magnetic tape with all necessary printing instructions such that the volumes are now being printed automatically by a photo-composing method. Beginning with the volume for the year 1984, the computations will be based on the IAU (1976) System of Astronomical Constants and related IAU recommendations. It will not be possible to include already in the volume for 1984 the star positions on the basis of the FK5. As soon as the FK5 will be completed the A.P.F.S. will be based on the FK5, and corrections will be given for the star places published for 1984 and possibly also for 1985. The equinox correction, however, namely ~a = 0:0775 + 0:085 T , where T is counted in Julian centuries from J2000.0, will be included in all right ascensions in the 1984 and following volumes. For the status of FK5, reference should be made to the Report of Commission 8 (W Fricke).

III. THEORY OF NUTATION

The XVIIth General Assembly of the IAU at Montreal in 1979 has adopted the "1979 IAUTheory of Nutation" (Trans. IAU XVIIB pp 80-83) upon recommendation of the IAU Working Group on Nutation. Subsequently the IUGG passed a resolution requesting that this action be reconsidered in favor of a theory based on a different Earth model. After wide discussions, also at the IAU Colloquium in September 1980, the Working Group proposed a revised nutation series, labeled "1980 IAU Theory of Nutation". By mail votes of the members of Commissions 4, 7, 8, 19, 24 and 31, the majority agreed that the theory adopted at Montreal should be replaced by the revised version. The complete "Final Report of the IAU Working Group on Nutation" will be printed in 'Celestial Mechanics'; it seems, however, useful to pUb-: lish the Summary of it in the APPENDIX to ~his Commission Report.

IV. RELATIONSHIP BETWEEN UNIVERSAL AND SIDEREAL TIME

The IAU (1976) System of Astronomical Constants, adopted at the XVIth General Assembly of the IAU at Grenoble in 1976, contained a Reco~ndation {3(c)} saying that "the expression for Greenwich mean sidereal time at 0 UT shall be amended ..... in order to avoid a discontinuity in UT" (Trans. IAU XVIB P 59). In 1979 at Montreal a Resolution was adopted by which the "relationship between mean sidereal time and UT1 be modified so that there is no change in either value or rate of UT1" (Trans. IAU XVIIB pp 41 and 66-67). That modification, however, was not sufficient to maintain the continuity of UT1 because it considered the equinox correction only. But one would have to take into account also the change of the precessional quantities (other, smaller effects can be compensated for by corrections to the longitudes of the instrument by which UTO is being determined). In connection with the discussions for a revised expression to be proposed for adoption in 1982, two controversial points of view concerning definitorial questions became involved. Communications will be available in two papers: (a) S Aoki, B Guinot, G H Kaplan, H Kinoshita, D D McCarthy, P K Seidelmann: 'The New Definition of Universal Time' (A & A, in press); (b) S Aoki, H Kinoshita: 'Note on the Relation between the Equinox and Guinot's Non-rotating Origin' (Celestial Mechanics, in press).

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COMMISSION 4

V. LUNAR, PLANETARY AND SATELLITE RESEARCH

Dr Seidelmann reports: "Planetary ephemerides using the IAU 1976 system of Astronomical Constants and the equator and equinox of the FK5 (J2000.0) have been developed by G H Kaplan, K F Pulkkinen, E J Santoro, T C Van Flandern and P K Seidelmann. This activity has been in cooperation with work being done by E M Standish and J G Williams at the Jet Propulsion Laboratory and C Oesterwinter at the Naval Surface Weapons Center, Dahlgren, Virginia. This effort along with the work of R S Harrington, has indicated the presence of systematic errors between the observations and the ephemerides of some of the outer planets. One of the hypotheses being investigated would be another planet beyond Pluto. L E Doggett has successfully developed a means of calculating planetary ephemerides by means of Chebychev polynomials to accuracy limited only by the computer precision. "T C Van Flandern and M R Lukac have analyzed occultation timings covering the period 1820 to 1979 to determine the difference between dynamical and universal time. This history of the variation of the Earth rotation rate discloses an especially large change in 1896. "Some investigators have suggested that the radius of the Sun may be changing significantly over a long period of time. This was based on a long series of transit records. As a result of this, A D Fiala entered into collaboration with S Sophia of NASA/GSFC and D W Dunham of Computer Science Corp. to study the use of solar eclipse observations to detect changes in the solar radius. This program requires the timings of eclipse phenomena near the edges of the central path. "D Pascu has made photographic observations of the Galilean moons of Jupiter and Saturn satellites I-VIII with the 26-inch refractor. In March 1980, D Pascu and P K Seidelmann participated with W A Baum of Lowell Observatory and D Currie of the University of Maryland in an observing program on the 61-inch telescope at Flagstaff, Arizona; using the 500 x 500 pixel charge coupled device (CCD) ground camera of the Space Telescope Widefield/Planetary camera team. Observations were made of the Saturn system during the crossing of the Saturn ring plane by the Earth. This observing program resulted in the detection of the E ring of Saturn and a number of observations of satellite images. From 30 April to 8 May 1981 further CCD camera observations were made with the 61-inch telescope. During this period, an 800 x 800 pixel Texas Instrument CCD was installed in the camera. T C Van Flandern and K F Pulkkinen have analyzed the astrometric observations of Pluto to determine the orbital period of Charon and carried out similar analysis on observations of Neptune to determine the orbital period of Triton." Dr Morando writes: "New theories for the motion of the planets and the Moon will be used in the Connaissance des Temps from 1984 onwards. The theories for the Sun and inferior planets which will replace the old ones, were made by P Bretagnon, the theory for Jupiter, Saturn, Uranus and Neptune by P Bretagnon and J L Simon. The theory of the motion of the Moon, which will replace the ILE, was made by M Chapront-Touze and J Chapront; this theory is called ELP2000-82. When building up those theories, the authors have chosen to use, as often as possible, the IAU System of Astronomical Constants (IAU-76), namely: the masses of the planets, the geocentric constant of gravitation, the harmonics of the gravity field of the Earth. The theories have been adjusted to observations via numerical integrations of the NWL and JPL, mainly through DE102 for the planets and LE51 for the Moon." From the report of Dr Abalakin: "M D Kislik et al. have constructed a numerical theory of Mars motion based on 2654 radar measurements and 4465 optical observations, the parameters being fitted over the interval of 1964-1971. This work has been extended further on on other inner planets being based on 3768 radar measurements (1962-1980) and on 7193 positional observations (1960-1976). The residuals do not exceed 6 km for Venus and 10 km for Mars. The similar theories for the inner planets' motions have been constructed by E L Akim et al. as well as by G A Krasinski et al .. M D Kislik has also investigated the relativistic effects influenc-

EPHEMERIDES

5

ing the planetary orbits determinations when making use of radar measurements, the necessary corrections to radar observations being thoroughly studied. The numerical approach to the study of all major planets' motions has been chosen by V P Dolgachyov et al. on the time interval of 1950-2150, and the secular variations of the longitudes of perihelia of Mercury's and Mars' orbits as well as of the longitude of the ascending node of Venus' orbit have been determined. The same authors have determined the values of time derivatives of1D and ~ for the inner planets making use of numerical integration of the differential equations of planetary motions in the gravitation field of the ellipsoidal Sun, its flattening E being equal to 5 parts in 10 4 • The results are found to be in fairly good agreement with observations. V A Izvekov has continued and completed his work on refinement of orbital parameters of Venus by use of radar and optical observations. Yu V Barkin has studied periodic perturbations in the translational motion and in the rotation of the Moon and Mercury. He has also investigated the perturbations in the Moon's orbital motion arising from the third and higher harmonics of the force function expansion for the Moon. N I Kolosnitsyn and A V Osipova have studied the perturbations in the heliocentric radii-vectors of Venus and Mars as well as in the geocentric radius-vector of the Moon due to violation of the equivalence principle. "A series of papers by V V Beletsky et al. was concerned with the problem of the resonances in the Venus' rotation. The value of the inclination of the Venus' equator to the plane of its orbit is found to be.equal to 51' with the mean error of ~17'. D Z Koenov has estimated the magnitude of periodic perturbations in the Earth's diurnal rotation due to the Moon's influence the period of these perturbations being found to be equal to 9000 ys. The shortening of the length of the day in 1979 was equal to 4 parts in 10 4 in seconds per day. Yu G Markov has applied the Poincare's theory of periodic solutions to investigations of the Moon's rotation making use of osculating canonical Andoyer's elements. The resonant libration of the Moon arising from the 2-term has been investigated by A S Dubrovsky and K S Shakirov; they have also found the most probable value of the Moon's physical constant f. The parameter f has been also considered by Yu A Chikanov and K S Shakirov. "The motion of distant satellites of a major planet has been studied by N B Batuyeva on the basis of the generalized Hill's problem. I G Chugunov has considered the perturbed motion of Saturn's satellites, the theoretical results being compared against observations. He has also studied the mutual perturbations of Saturn's satellites. A A Orlov and V M Chepurova have investigated solar short-periodic perturbations of the fourth order in the motions of satellites of major planets. "D P Duma et al. have corrected the zero-points of the FK4 fundamental system on the basis of analysis of 2441 Mercury optical observations made in 1929-1971, 6957 Venus positional observations (1929-1971), 1834 Mars observations (1941-1971) as well as observations of Ceres, Pallas, Juno, and Vesta. The similar investigations have been made by V I Orelskaya who had used observations of the selected minor planets. The dependence of computed ephemerides positions of planets on errors in orientation of coordinate systems of star catalogues has been investigated and analyzed by D P Duma et al. By D D Polozhentsev have been determined the parameters of the Sun's space motion and of the Galaxy's rotation as well as the correction to the precession constant, the work being done on the basis of the analysis of the proper motions system in right ascension of the general star catalogue compiled for the southern sky hemisphere. "Yu S Yatskiv has given a review of the recent version of the theory of the astronomical nutation in connection with the new IAU system of astronomical constants. The IAU system of astronomical constants (1976, 1979) has been also reviewed by V K Abalakin. New rotational parameters for major planets and their satellites as well as the parameters defining new systems of planetographic (or cartographic) coordinates which were recommended in 1979 by the IAU Joint Working Group have been considered by Yu S Tyuflin and V K Abalakin. V K Abalakin has outlined the intrinsic ties connecting the Ephemeris astronomy with celestial mechanics and Astrometry. "The algorithms for representing the fundamental precise ephemerides data by means of Chebyshev's polynomials have been worked out by M A Fursenko, the corresponding FORTRAN IV procedures being also developed. The same problem for rectan-

6

COMMISSION 4

gular planets' coordinates has been approached by E Z Khotimskaya. V N L'vov and S V Serova have constructed the algorithm for computation of stars' apparent ephemerides in the rectangular coordinates based on the recommendations of the XVllth IAU General Assembly concerned with the reduction techniques and the IAU system of astronomical constants, the accuracy of ~0~001 being secured. V N L'vov has compiled also a package of routines designed for ephemerides computation for radio astronomical observations of quasars and radio emitting objects within the Solar systems. "M L Sveshnikov has compared the Sun's positional observations made in T9111970 at the USNO, Washington, with Newcomb's theory. Further developments of numerical integration methods with regularization based on Taylor type expansions (the Taylor-Steffensen methods) have been continued by V F Myachin and 0 A Sizova. V A Brumberg et al. have treated the problem dealing with comparison of a theory with observations and accounting for the relativity effects. V A Izvekov has investigated the ephemerides computation process for the case where the ill-conditioned systems of normal equations must be solved." Dr Aoki writes: "A second-order theory of the motion of Mars has been constructed at the Tokyo Astronomical Observatory and is found to be slightly better than the theory by G M Clemence. A third-order theory is necessary for achievement of ~01 accuracy. Planetary ephemerides, VSOP80, have been compared with numerical integration over 35 years at the Tokyo Astronomical Observatory. They achieve ~01 accuracy (RMS residuals) for inner planets and ~1 accuracy for outer planets. Lunar ephemerides, ELP2000 and SALE2000, have been compared with numerical integration. As for as the main problem is concerned, ELP2000 has 1.2 cm accuracy (RMS residuals) over one year in the distance (H Kinoshita). "H Niimi found the set of orbital elements of Mars in Clemence's theory without empirical secular term and the equator and equinox corrections to FK4 system from meridian observations, covering the period from 1935 to 1976; the equator and equinox corrections are -0~08 and +07042, respectively. He found that there still remain systematic trends in the residuals, even after an improvement of orbital elements. The systematic trends seem to be due to the unaccounted phase effect." Report on ephemeris efforts at the Jet Propulsion Laboratory (Dr Lieske): "During the past three years efforts have continued at JPL to produce highly accurate planetary, lunar, and satellite ephemerides for use in the NASA space program and for international investigations which require high accuracy. Investigations and cooperative efforts with other scientists have been undertaken to more clearly understand the similarities and differences between JPL ephemerides and the classical ephemer~des of Newcomb, as well as for obtaining a greater understanding of the underlying astronomical constants. Cooperative investigations have been made with Bretagnon and Chapront at the Bureau des Longitudes, with Stumpff in Bonn, with Schubart and Fricke in Heidelberg, and with the USNO, Washington. Efforts have also continued for the development and production of highly accurate satellite ephemerides for the Voyager and Galileo NASA missions. Several thousand 17th and 18th century eclipse observations of the Galilean satellites have been discovered which should lead to a better understanding of the variations in ~T, as well as possible evolution of the Laplacian commensurability for the Galilean satellites. The planetary and lunar ephemeris recommended for the MERIT campaign is Development Ephemeris Number DE200/LE200. It has been produced at the Jet Propulsion Laboratory in collaboration with members of the United States Naval Observatory. It will form the basis of the Astronomical Almanac starting in 1984 and most likely will be adopted by other national almanac offices as well. The ephemerides provide, by themselves, a dynamically consistent system whose reference frame has been accurately adjusted to the dynamical equinox of J2000.0. Furthermore, the relative positions and velocities of the four inner planets and moon are well-determined and their mean motions are accurately represented with respect to inertial space. "With such an accurately determined system (positions, velocities, inertial mean motions, masses, and true obliquity), it has been possible to locate the actual

EPHEMERIDES

7

dynamical equinox of DE200/LE200 at the origin of the reference system. This was done through a detailed analysis of the Earth-Moon barycenter's orbital motion and a subsequent adjustment of the coordinate axis. An independent determination by Bretagnon and ChajJront indicates that this procedure is accurate to at least 0,'001. "One may note that the reference frame of the ephemerides will not strictly coincide with the origin of the FK5 catalog system. The difference will be the amount by which the origin of the FK5 itself fails to coincide with the dynamical equinox of J2000.0. However, the ephemeris-FK5 difference should actually be much smaller than it would be if an attempt were made to align the ephemeris system directly to the FK5 through the use of optical planetary observations. As such, the above procedure for orienting the planetary ephemeris to the dynamical equinox of J2000.0 is strongly justified. In actuality, the adjustment angle used in DE200/ LE200 of 0':53087 is surprisingly close to that of 0':525 which will be used by Fricke for the FK5."

VI. MISCELLANEOUS

(a) Lunar occultations. The Hydrographic Department of Japan took over the services of the International Lunar Occultation Centre (ILOC) from the Nautical Almanac Office of the Royal Greenwich Observatory on 1981 January 1, in accordance with the resolution of Commission 4 at the IAU XVllth General Assembly held in Montreal. Since then, timing data of lunar occultations are collected and some predictions are provided by the new ILOC. The reduction system is also being developed at the Centre. HM Nautical Almanac Office, Herstmonceux, continues to provide predictions of occultations by minor planets and satellites. (b) Astronomical Constants. At its XVllth General Assembly at Canberra in December 1979 the IUGG has adopted a new "Geodetic Reference System 1980" (Bull. Geod. 54, p 370). Note that the numerical value for the equatorial radius of the Earth is there 6 378 137 m (compared with 6 378 140 m in the IAU (1976) System of Constants).

T. LEDERLE Vice-President of the Commission

COMMISSION 4

8

APPENDIX SUMMARY OF 1980 IAU THEORY OF NUTATION (Final Report of the IAU Working Group on Nutation)

1. The President of IAU Commission 4, Dr. V K Abalakin, established the Working Group on Nutation at the request of IAU Symposium No. 78 on Nutation and the Earth's Rotation, held at Kiev in May 1977. The final membership of the Working Group comprise the authors of this report. 2. The theory of nutation currently in use is due to E W Woolard (Astr. Papers Amer. Ephemeris XV, Pt. I, 1953) and has the following characteristics: (a) It is based on a rigid model of the Earth with dynamical axisymmetry (A=B) •

(b) The "constant of nutation" is an empirical value and is not consistent with other adopted astronomical constants. (c) Eulerian motion and forced nearly-diurnal polar motion are not included in the current theory of nutation, but are assumed to be part of polar motion. (d) The pole of reference is the instantaneous celestial rotation pole. 3. Modern theoretical and observational developments of various types have revealed the following problems with the current theory of nutation: (a) The Earth is not a rigid body and the effects of non-rigidity can be observationally significant. (b) Determinations of UTi and polar motion using optical observations of stars, Doppler and laser range tracking of satellites, laser ranges to the Moon, and radio interferometric measurements are sufficiently accurate that their usefulness can be degraded by use of the present theory of nutation in the data reduction process. (c) As Jeffreys and Atkinson pointed out, the instantaneous axis of rotation as defined by Woolard rotates relative to an Earth-fixed coordinate system with a quasi-diurnal period. For accurate observation reduction, this rotation cannot be ignored and a resolution was passed at the Sixteenth General Assembly of the IAU in 1976 in Grenoble to adopt a different pole of reference. (d) Observational data indicate that with the current (Woolard) theory of nutation and a redefined pole of reference, a body-fixed coordinate system would still rotate with respect to the reference pole; therefore, the theory of nutation should be revised. In proposing a theory of nutation to the Montreal IAU General Assembly in 1979, the Working Group sought to present a numerical expression that represented nutation with an accuracy better than existing astronomical observations. Two series were considered; both based upon Kinoshita's rigid-body calculations but differing slightly in how the effects of the Earth's deformability were accommodated. The first series was prepared by Kinoshita and co-workers and used the well-known results given by Molodensky in 1961. The other series, due to Wahr, had become available to the Working Group only a few months before the IAU meeting; it had not yet been published and, hence was not widely known. Furthermore, it was clear that for any known astronomical application, the differences between the series were not currently detectable. Thus, both series satisfied the Working Group's requirements for a theory of nutation for astronomical observations. 4. In August 1979, the General Assembly of the IAU at the recommendation of the Working Group adopted the 1979 IAU Theory of Nutation, which was based on the

EPHEMERIDES

rigid-body theory of Kinoshita and the deformable theory for Earth model No. 2 by Molodensky. At that time it was emphasized that this action was the adoption of a set of nutation coefficients and not the endorsement of a particular Earth model. In December 1979 the International Union of Geodesy and Geophysics (IUGG) adopted a resolution requesting that the IAU reconsider its choice of a nutation series. The IUGG objection to the IAU resolution was not based on a criticism of the numerical values of the coefficients of the nutation theory, but rather on their interpretation that the IAU had implicitly endorsed the Molodensky Earth model 2, which was no longer judged adequate on geophysical grounds. Wahr's results, on the other hand, were obtained using a representative model available in 1979. The IAU has avoided this misunderstanding by accepting the IUGG suggestion. The IUGG believes that the model on which Wahr's computations are based (the model 1066A of Gilbert and Dziewonski) is the best Earth model presently available and that observed geophysical constraints are such that any modern Earth model would have to be very similar. This implies that the observational residuals that result from the use of the Wahr nutation series will be more meaningful, geophysically. On the other hand, since the IUGG objections were predicated on the question of the choice of Earth model, changing to the Wahr series implies at least an indirect endorsement by the IAU of the IUGG's preferred Earth model. This is not necessarily bad, especially in view of the belief that future models will not differ appreciably so far as nutation is concerned, but it must be clear that the nutation series will not be changed in the near future in response to shifts in the Earth model preferred by the IUGG. After considerable correspondence and a discussion at IAU Colloquium 56 in September 1980 in Warsaw, Poland, the process of changing to the 1980 IAU Theory of Nutation was initiated. Clearly the situation has changed since the General Assembly in Montreal and it is advisable to make any adjustments before the 1979 theory has been introduced into wide spread use. Therefore, with the approval of the General Secretary the IAU Commissions involved voted by mail to adopt the 1980 Theory of Nutation. 5. The goal of this report is the adoption of a set of nutation coefficients which will provide an adequate working standard for determination of UT1 and polar motion, the reduction of optical observations of stars, Doppler or laser range tracking of satellites, laser ranges to the Moon, radio interferometric measurements and other high precision requirements. 6. Therefore, the proposed solution incorporates the following changes: (a) A non-rigid model of the Earth without axial symmetry is used. This model of the Earth is subject to tidal distortions, has a solid inner core, fluid outer core, but no oceans. (b) The constants are consistent with the 1976 IAU System of Astronomical Constants and are in agreement with available observational data of various types. (c) The reference pole is selected so that there are no diurnal or quasi-diurnal motions of this pole with respect to either a space-fixed or Earthfixed coordinate system. The phenomenon of dynamical variation of latitude, otherwise known as forced diurnal polar motion, is included implicitly in the new nutation theory. The new nutation theory thus includes externally-forced motions of the Earth's rotation axis, but does not include free motions or such complex phenomena as ocean tides, atmospheric winds, and currents in the oceans or core. The new reference pole shall be referred to as the "Celestial Ephemeris Pole" (CEP).

9

10

COMMISSION 4

7. The new nutation theory, incorporating the above changes, is given in Table I and shall be referred to as the "1980 lAD Theory of Nutation". This nutation theory was developed by Wahr (29.081.005) based on previous work by H Kinoshita (20.042.046) and F Gilbert and A M Dziewonski (Phil. Trans. R. Soc. London A 278, 187, 1975). The fundamental arguments for the nutation theory are given in Table II. P V H J

K Seidelmann, Chairman K Abalakin C A Murray Kinoshita M L Smith Kovalevsky R 0 Vicente

J G Williams Ya S Yatskiv

TABLE I Nutation in Longitude and Obliquity referred to mean ecliptic of date Epoch J2000.0 (JD 2451545.0 TDB) T in Julian Centuries Argument 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

1' F

D

0 0 0 0 0 0 0 2 0 0 -2 0 0 2 0 -1 0 -1 -2 2 -2 0 -2 0 0 2 -2 0 0 2 -2 -1 2 -2 0 2 -2 0 0 -2 0 2 -2 2 0 0 0 0 2 2 -2 -1 0 0 0 0 2 -1 2 -2 0 0 -2 1 2 -2 0 0 -1 2 0 -2

0 0 -2 2 -2 1 0 2 0 0 0 0 0 2 0 0 0 0 0 -2 0 2 0

0

2 0 2 0

2 0 2 2 0 0 0 1 2 1

1 0 0

Period (days) 6798.4 3399.2 1305.5 1095.2 1615.7 3232.9 6786.3 943.2 182.6 365.3 121.7 365.2 177 .8 205.9 173.3 182.6 386.0 91.3 346.6 199.8 346.6 212.3 119.6 411. 8 131.7

Longitude (~'OOOI ) -171996 2062 46 11 -3 -3 -2 -13187 1426 -517 217 129 48 -22 17 -15 -16 -12 -6 -5 4 4 -4

-174.2T .2T O.OT O.OT O.OT O.OT O.OT O.OT -1.6T -3.4T 1.2T -.5T .IT O.OT O.OT - .IT O.OT .IT o .OT O.OT O.OT O.OT O.OT O.OT O.OT

Obliquity (':0001) 92025 -895 -24 0 0 0 5736 54 224 -95 -70 0 0

9 7 6 3 3 -2 -2 0 0

8.9T .5T O.OT O.OT O.OT O.OT O.OT O.OT -3.1T -.IT -.6T .3T O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT

EPHEMERIDES

TABLE I

11

(continued)

Nutation in Longitude and Obliquity referred to mean ecliptic of date Epoch J2000.0 (JD 2451545.0 TDB) T in Julian Centuries

1

26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67

o o o

-1

o o

Argument l' F D

0 -2 1 -2

Q

2 2

1 0

100 0 0

2

2 -2 0 0 2 0 2 o 0 0 0 o 0 2 0 1 0 202 1 0 0 -2 0 -1 0 2 0 2 00020 1 000 -1 0 0 0 1 -1 0 2 2 2 1 0 2 0 00222 2 000 0 1 0 2 -2 2 2 0 2 0 2 o 0 2 0 0 -1 0 2 0 1 -1 0 0 2 o 0-2 -1 0 2 2 o -2 0 020 2 o -1 2 0 2 o 2 2 2 o 0 2 0 2 0 2 -2 2 00021 o 0 2 2 o 2 -2 o 0 o -2 -1 o 0 o 2 0 2 0 1 o -2 o o o -2 0 0 00010 1 1 0 0 0 o 2 0 0

Period (days) 169.0 329.8 409.2 388.3 117.5 13.7 27.6 13.6 9.1 31.8 27.1 14.8 27.7 27.4 9.6 9.1 7.1 13.8 23.9 6.9 13.6 27.0 32.0 31.7 9.5 34.8 13.2 14.2 5.6 9.6 12.8 14.8 7.1 23.9 14.7 29.8 6.9 15.4 26.9 29.5 25.6 9.1

Longitude (':0001)

-1

-1

-2274 712 -386 -301 -158 123 63 63 -58 -59 -51 -38 29 29 -31 26 21 16 -13 -10 -7 7

-7 -8 6 6 -6 -7 6 -5 5

-5 -4 4

-4 -3 3

O.OT O.OT O.OT O.OT O.OT -.2T .1T -.4T O.OT O.OT O.OT O.OT .1T -.1T O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT

Obliquity (~'0001)

o o a o o

977

-7 200 129 -1 -53 -2 -33 32 26 27 16 -1 -12 13 -1 -10 -8 7 5

o

-3 3 3

o -3 3 3

-3 3

o 3

o o o o o

O.OT O.OT O.OT O.OT O.OT -.5T O.OT O.OT -.1T O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT

12

COMMISSION 4

TABLE I

(continued)

Nutation in Longitude and Obliquity referred to mean ecliptic of date Epoch J2000.0 (JD 2451545.0 TDB) T in Julian Centuries

1 68 69 70 71 72

73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106

Argument l' F D

r2

-1 2 0 2 -1 -1 2 2 2 -2 0 0 0 3 0 2 0 2 o -1 2 2 2 1 202 -1 0 2 -2 1 2 0 0 0 1 000 2 3 0 0 0 0 00212 -1 0 0 0 2 o 0 -4 0 -2 0 2 2 2 -1 0 2 4 2 2 0 0 -4 0 1 2 -2 2 022 1 -2 0 2 4 2 -1 0 4 0 2 1 -1 0-2 o 2 0 2-2 1 2

0

2

2

100 2 o 0 4-2 3 0 2-2 1 0 2-2 o 1 2 0 -1 -1 0 2 o 0 -2 0 o 0 2-1 002 o -2 -2 o -1 2 0 o -2

o

-2

2

2 1 2 2

o 1 1 2

a

a 1

a o

200 2 0 242 000

o

Period (days)

Longitude (~OOOI)

9.4 9.8 13.7 5.5 7.2 8.9 32.6 13.8 27.8 9.2 9.3 27.3 10.1 14.6 5.8 15.9 22.5 5.6 7.3 9.1 29.3 12.8 4.7 9.6 12.7 8.7 23.8 13.1 35.0 13.6 25.4 14.2 9.5 14.2 34.7 32.8 7.1 4.8 27.3

EJ2aOO

-3 -3 -2 -3 -3 2

-2 2

-2 2 2 1 -1

-2 -1

1 -1 -1

1 1 1 -1 -1 1

-1 1

-1 -1 -1 -1

-1 . -1

-1 -1

=

23°26'21~448

sin EJ2aOO

=

.39777716

O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT

Obliquity (,'0001 )

-1

1 -1

o

-1 -1

o

-1

o

-1

1

o o

-1

o o o o o o o o o o o o o

o o o o

O.OT O.OT O.OT O.OT O.OT O.OT o .OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT O.OT a.OT O.OT O.OT O.OT a.OT O.OT O.OT a.OT a.OT a.OT

EPHEMERIDES

13

TABLE II Fundamental Arguments The fundamental arguments in the FK5 reference system are (Van Flandern, Astr J, 1981, in press): 1

134°57'46~733 + (1325r+198°52'02~633)T + 31~310T2 + 0~064T3

l'

357°31'39~804 + (99r+359°03'01~224)T - 0~577T2 - 0~012T3

F

93°16'i8~877 + (1342r+82°01'03~137)T - 13~257T2 + 0~011T3

D

297 0 51 '01 ~'307 + (1236 r +307°06 '41 '!328)T - 6'!891T2 + 0~'019T3

n

125°02'40~280 -

(5r+134°08'10~539)T + 7~455T2 + 0~008T3

where the fundamental epoch is J2000.0 and lr

=

360 0

=

d

2000 January 1.5 TDB

=

JD 2451545.0 TDB,

= 1296000~0,

T is measured in Julian centuries of 36525. days of 86400 seconds of dynamical time each, 1 = mean longitude of the Moon minus the mean longitude of the Moon's perigee,

l ' = mean longitude of the Sun minus the mean longitude of the Sun's perigee, F

mean longitude of the Moon minus the mean longitude of the Moon's node,

D

mean elongation of the Moon from the Sun,

n

longitude of the mean ascending node of the lunar orbit on the ecliptic, measured from the mean equinox of date.

Note that the fundamental arguments are the best values currently available for the FK5 reference system and the 1976 IAU constants. These values may change slightly based on an improved lunar ephemeris, but the changes will not significantly affect the nutation theory. It is possible that the different expressions should be used for work which depends in a very critical way on the precise solar or lunar theories; however, nutation theory is not in this class of work. Therefore the above expressions, while provisional, are of sufficient accuracy for the evaluation of the nutation theory to O~'OOOI.

COMMISSION 5.

DOCUMENTATION AND ASTRONOMICAL DATA DOCUMENTATION ET DONNEES ASTRONOMIQUES

PRESIDENT: W.D.Heintz. VICE-PRESIDENT: G.A.Wilkins. ORGANIZING COMMITTEE: B.Hauck, J.Kleczek, P.Lantos, S.Mitton, J.-C.Pecker, L.Schmadel, I.Shcherbina-Samojlova. The range of activities of Commission 5 has considerably broadened over the last decade, compared with its originally bibliographical emphasis. This fact is also reflected in the new name of this Commission as adopted at the Montreal conference. The increased production of astronomical data, the growing role of data centers in the organisation and retrieval of information, as well as the editorial and bibliographic processing of the large number of primary papers have indicated the need for new and more efficient coordinative guidelines. Several documents have been published and are under consideration, or are in preparation, for the agenda at the IAU General Assembly in 1982. B.Hauck is the IAU Representative on CODATA (ICSU Committee on Data for Science and Technology), with G.Wilkins representing the Federation of Astronomical and Geodetical Services (FAGS). Meetings of the ICSU Abstracting Board have been attended by L.Schmadel, P.Lantos, and W.Heintz, the latter also serving on the Executive Committee of the Board for the IAU term of office. S.Mitton succeeded J.Shakeshaft on the Organizing Committee of Commission 5. Most of the activities are within the realms of the Working Groups on Astronomical Data (chaired by B.Hauck) , on Classification Systems and Information Retrieval (P.Lantos) , on Editorial Policy (S.Mitton), and the Special Working Group on the Designation of Astronomical Objects (W.Bidelman). Publications related to this work will be found primarily in the Bulletin d'information du Centre de Donnees Stellaires (Strasbourg, ed. C.Jaschek) and in the CODATA Bulletin. IAU Colloquium no. 64 was h~ld in Strasbourg on July 7 - 10, 1981 by Commission 5, the WG on Data, and the CDS, chaired by C.Jaschek. The title "Automated Data Retrieval in Astronomy" indicates its emphasis, although the spectrum of the more than fifty papers covered the efforts and problems in documentation more broadly. The proceedings are being prepared for publication in the Reidel series of IAU Colloquia. The IAU has financially supported the publication of the revised index of catalogues under supervision by F.Spite; the work will be available shortly. Also supported was the new Multilingual Dictionary by J.Kleczek. The IAU Style Book, first published by J.-C.Pecker in 1966 (IAU Trans. XII C), and occasionally amended since, is undergoing a comprehensive revision by S.Mitton in consultation with the IAU. Under consideration is the addition of editorial guidelines, the inclusion of which has repeatedly been suggested. The Guide to the Presentation of Data, prepared by G.Wilkins along CODATA procedures, and already discussed in Montreal, has been redrafted, and received further discussion among Commission 5 members at the occasion of the Strasbourg meeting, before it was sent to other IAU Commissions for final comments preceding action at the next IAU Assembly. G.Wilkins has also prepared a Proposal for a Glossary of Terms Relating to the Storage, Retrieval and Analysis of Astronomical Data (Bulletin CDS 11, 47-49). The following ProgrEss Reports (in continuation of those in IAU Trans. XVII A, pt.1, p.7) have been received. 15

16

COMMISSION 5

Working Group on Astronomical Data (Report for the period 1979-81 by B.Hauck): The main activity of our WG was devoted to trying to centralize the information concerning the astronomical plate vaults. An inquiry of a large number of observatories revealed that the majority of people concerned are in favour of such centralisation. The CDS at Strasbourg has agreed to act as centralizer. Details concerning this action will be published in the proceedings of the IAU Colloquium No.64. Our WG was also interested in the Flexible Image Transport System (FITS, see D.C.Wells et al., A.A.Suppl. 44, 363; E.W.Greisen and R.H.Harten, A.A.Suppl. 44, 371, 1981) and will support this very valuable solution for the exchange of data. During the period covered by this report we have seen the development of astronomical data networks: STARLINK in the U.K., ASTRONET in Italy, and another one in Japan. The development of stellar data centers is encouraging and the fact of having such centers in France, VSA, USSR, Japan and the DDR facilitates the access to astronomical data. The most important developments in this field are definitely the Catalogue of Stellar Identification (F.Ochsenbein et al., 1981, A.A.Suppl. 43, 259) at the CDS, Strasbourg, and the Infrared Data Base at the GSFC, Greenbelt, Maryland (see D.Schmitz et al., 1981, Astron.Data Center Bull. 1, 94). CODATA's scientific conference was held at Kyoto (October 8-11, 1980). The proceedings of this conference are now available (Ph. Glaeser, Data for Science and Technology, Pergamon Press, 1981). Working Group on Classification Systems and Information Retrieval (Report by P.Lantos): Le travail du groupe de travail s'est centre sur Ie souhait de la Commission 5 durant l'Assemblee Generale de l'U.A.I. de Montreal de voir preparer un vocabulaire d'Astronomie qui puisse etre utilise par les auteurs pour indexer leurs propres articles scientifiques. Le WG se compose de R.Bensaid (France), Mme C.Berardini (France), M.J.Collins (U.K.), P.Lantos (chairman; France), L.D.Schmadel (BRD) , S.Schiminovich (USA), and G.A.Wilkins (U.K.). 11 s'est reuni une premiere fois a Strasbourg en Juillet 1981. Une version de travail du vocabulaire a ete cree sur Ie principe d'une compatibilite avec les listes de mots clefs deja existentes qu'elles proviennent des services bibliographiques (comme Ie AAA vocabulary) ou des revues primaires (Astrophys.J., Astr.Astrophys.) qui s'en servent pour leur index annuel. 11 a semble souhaitable que ce vocabulaire soit aussi compatible avec la classification decimale universelle (Federation Internationale de Documentation) et avec la classification de Physique mise au point dans Ie cadre de l'ICSU AB. Cette classification internationale est en effet adoptee par la majorite des services publiant des revues bibliographiques: AlP (USA), INSPEC (UK), CNRS (France), Physikalische Berichte (BRD). Le vocabulaire contient environ 1000 mots clefs. 11 sera soumis a des experts de chaque discipline de l'Astronomie et de l'Astrophysique et une ~~union du Working Group est prevue pour Ie printemps 1982 afin de confronter les points de vue. Si un accord est obtenue, Ie vocabulaire UAI pourra etre presente a la Commission 5 lors de Assemblee G~nerale de Patras durant l'ete 1982. Special Working Group on Designation of Astronomical Objects (W.Bidelman): Following the suggestion by Commission 5 to allow further discussion of the matter on hand, the entire Report of this WG has been published in Bulletin CDS 18, p.44, 1980, including the full text of the recommendations (which are modified slightly in form from those printed in IAU Trans. XVII B, p.87). It is urged that

DOCUMENTATION AND ASTRONOMICAL DATA

17

interested colleagues consult this paper and submit comments before report and recommendations will be moved for adoption by the entire Commission and by the IAU EC in Patras. With this task discharged, the Commission should also consider at that time whether the Working Subgroup be disbanded, or be reconstituted for work on farther-reaching, related problems. Activity in Astronomical Documentation in the USSR (Report for the period 1978-80 by 1. S. Shcherbina-Samojlova, Head of the Astronomy and Geodesy Department, VINITI, Moscou); 1. The Astronomy and Geodesy Department of VINITI (All-Union Institute for Scientific and Technological Information) continued publication of subjects 51 (Astronomy), 62 (Space Research), and 52 (Geodesy and Aerial Surveying) of the Referativnyi Zhurnal. The number of abstracts totalled 20,000 annually in three issues. 2. New volumes in the series Itogi Nauki (state-of-the-art reviews) are: Series Astronomy; 1978, vol.14, Solar Physics. 1979, vol.15, Asteroids: Origin, Statistics, Evolution. 1980, vol.16, Radio exploration of the Moon and the terrestrial planets. Series Space Research: 1978, vol. 11, Some problems of Satellite Orientation. 1978, vol.12, Cosmic Rays of Solar Origin. 1979, vol.13, Solar Arrays under Influence of Solar Radiation. 1979, vol.14, Astronomy of Infrared and Sub-mm Range. 1980, vol. 15, Earth's Artificial Satellite Motions. 1980, vol. 16, Methods and Possibilities of Remote Sensing. 3. "Soviet Astronomy Bibliography for 20 years (1958-1977)" and "Annotating Index on the Moon and Related Investigations (1968-1980)" have been prepared for pUblication; the production of these volumes is delayed. 4. A collection of papers entitled "Informatics in Astronomy and Geodesy" is in press. (Abstracts of the papers have been sent to Commission 5.) 5. Work toward improvement of UDC 52 (Astronomy) continued, in particular, the following section proposals have been prepared: 523.9. The Sun. Solar Physics (jointly by the Natural Sciences Library, the Institute for the study of Geomagnetism, Ionosphere, and Radiowave Propagation, both of the Akademia Nauk USSR, and VINITI); 523.4. Stars (by VINITI and the Sternberg Astronomical Institute). 6. VINITI and the Astronomical Observatory of Kharkow University constructed an Accordance Table between UDC 52 and the Rubricator of the Referativnyi Zhurnal Astronomy. This document will be distributed for use in all astronomical institutes and editorial offices, since the UDC is the official classification system of all scientific and technical publications prin·ted in the USSR. 7. Compilation of a thesaurus of astronomical terminology was continued for future use in automatic information retrieval. 8. The following papers were published: T.I.Zapolskaya, I.S.Shcherbina-Samojlova, Selected Results from a Study of Astronomy Document Flow, with special reference to the Astronomy Abstract Journal; Nauchno-Techniceskaya Informatsiya (NTI) , ser.I, no.9, 21-26. (Scientific and Technical Serial of VINITI, Moscou). I.S.Shcherbina-Samojlova, V.T.Fedorov, Primary and Secondary Journals in Radio Astronomy; NTI ser.I, no.l, 23-27, 1979. T.I.Zapolskaya, I.S.Shcherbina-Samojlova, Analysis of Information Flow Dynamics as a Method of Studying the Development of Astronomy and its Sections.

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NTI ser.I, no.9, 23-30,1979. T.I.Zapolskaya, G.S.Shvedova, I.S.Shcherbina-Sarnojlova, Information Supply to the Specialists of Astronomical Observatories (with the example of the Special Astropysical Observatory of the USSR Akademia Nauk; NTI ser.I, no.12, 11-12, 1980. V.T.Fedorov, The Basic Elements of Scientific Publications and their Analysis; Radiophysical Institute in Gor'kij, Preprint no.135, 1980. Other Abstracting Services in Astronomy and related fields: The latest reports have been presented at the meeting of the Abstracting Board in Pine Mountain (Georgia) in May 1981. Star catalogs and files available at the Stellar Data Center (Strasbourg): The Bulletin CDS ll, 52 - 117 provides a new, cumulative listing which supersedes previous lists. W.D.HEINTZ President of the Commission.

6.

ASTRONOMICAL TELEGRAMS (TELEGRAMMES ASTRONOMIQUES) (Committee of the Executive Committee)

PRESIDENT: J. Hers VICE-PRESIDENT: M.P. Candy DIRECTOR OF THE BUREAU: B.G. Marsden, Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA TWX: 710-320-6842 ASTROGRAM CAM Telephone: (617) 864-5758 ASSOCIATE DIRECTOR OF THE BUREAU: vacant ASSISTANT DIRECTORS OF THE BUREAU: C.M. Bardwell, D.W.E. Green

r.

INTRODUCTION

The Commission has been fortunate in being able to continue its work during the last triennium with a minimum of effort, and thanks for this should go largely to the Director of the Bureau, Dr B.G. Marsden, for his untiring dedication, as well as to the Smithsonian Astrophysical Observatory for its general support. If any question has arisen, it was where the line should be drawn between paid and unpaid contributions to the Circulars. This involves a somewhat delicate balance of interests between, on the one hand, the encouragement given to certain types of observations which have traditionally been published in the Circulars, (e.g. accurate positions of comets), and, on the other, the income on which the continued successful operation of the Bureau depends. The position will therefore have to be kept under review at all times. At present all evidence points to general satisfaction with current policy. Today's rapid development of new methods of electrical communications are causing the title "Astronomical Telegrams" to become almost a misnomer, and one can foresee the day when it will disappear entirely. One of the important activities of the Commission in the coming years is likely to be the study of these new methods. In time this may well lead to a far more rapid and comprehensive dissemination of astronomical data than is available today. J. HERS President of the Commission II.

REPORT OF THE CENTRAL BUREAU FOR ASTRONOMICAL TELEGRAMS

The Central Bureau for Astronomical Telegrams has operated much as usual during the triennium, the number of occasions on which "telegram books" and Circulars were issued being: Circulars

Telegrams 1978 (from 1 Nov.)

7

14 (Nos. 3298-3317)

1979

42

66 (Nos. 3318-3438)

1980

52

71

1981 (to 23 Oct.)

33

51 (Nos. 3558-3641 )

19

(Nos. 3439-3557)

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The slight reduction in the number of Circulars issued is an indication that researchers are publishing their mini-papers in more suitable places, a practice that Commission 6 has tried to encourage. This effect is in fact more real than the above figures indicate, since, rontrary to the situation before 1978, all the Circulars now consist of only 3 single page. Further, the proper activity of the Bureau is more appropriately indicated by the number of telegrams issued; these are of course also followed up in the Circulars, and the number of telegrams and such follow-up Circulars was in fact somewhat greater than during the previous triennium. The highlight of the triennium, amply documented in the Circulars published during 1980, has involved the new discoveries of satellites of Saturn. The fact that such discoveries should be made at this time was due to the passage of the Sun and the Earth through Saturn's ring plane. Following a recommendation by the IAU Working Group on Planetary System Nomenclature, the observations were registered with temporary designations until more "2tailed analysis could sort out the identifications among them. As many as 33 different provisional designations were supplied in 1980; these were found to refer to seven definite discrete objects and possibly more. Inflation has made it necessary to increase the subscription rates in several stages, up to 50c for regular and 30c for special accounts as of June 1981. There has been a slight drop in the number of subscribers, down to 809 by November 1981. The line charges for non-essential items were increased to $30.00 per item plus $10.00 per line.

Z. Sekanina resigned as Associate Director of the Central Bureau on his departure from the Smithsonian Astrophysical Observatory in October 1980. C.M. Bardwell has continued as an Assistant Director, and D.W.E. Green was promoted to this same position in April 1981. The position of Associate Director is vacant at this time. The TWX machines purchased by the Central Bureau in 1978 have continued to serve the process of telegraphic communication well, allowing messages to be received and transmitted 24 hours a day, 7 days a week. F.E. Cook, at the Ionospheric Prediction Service in Sydney, has generously relayed messages to subscribers in Australia and New Zealand, and World Data Center A for Solar-Terrestrial Physics, Boulder, has relayed them to Moscow for distribution in the USSR. B.G. MARSDEN Director of the Bureau

7

MECANIQUE CELESTECCELESTIAL MECHANICS)

PRESIDENT: Y Kozai VICE-PRESIDENT: J Kovalevsky ORGANIZING COMMITTEE: E P Aksenov, V A Brumberg, S Ferraz-Mello, J Hadjidemetriou, P J Message, J Schubart, P K Seidelmann, I

F Nahon, V Szebehely

INTRODUCTION

In the past three years progress of celestial mechanics research was as rapid as in the previous decade. In fact now new theories of planetary and lunar motions which have nearly the same accuracy as those of the most precise observations have become available after a decade effort and new thories of some of natural satellite motions have been developed by several authors. Many papers on artificial satellite motions from several aspects were still published and more precise expressions for relativistic effects were derived. Several faint satellites which have very interesting dynamical characters were discovered and very detailed structures of Saturnianrings as well as very narrow rings of Jupiter, Saturn and Uranus were disclosed. Therefore, much more papers than before treating resonance problems for satellites, rings, asteroids and so on, their stabilities and dynamical evolutions were published in the past three years, as there are now more resonance problems to be studied in the solar system. Commensurable relations exist not only among revolution periods but also among revolution and rotation periods. And, therefore, rotational motions of the moon and planets attract many authors to study their dynamical evolutions. As many high-speed computors have become accessible new types of periodic solutions for three and four body problems were found, some of them being periodic even in the three dimensional space. In fact many papers on periodic solutions were published. Some papers treat systems containing not only point masses but also one or more finite bodies and try to find their particular solutions. Mathematical theories to try to understand qualitative properties of solutions of the equations of motion in celestial mechanics made a steady progress and some important contributions on this subject were published. In spite of the rapid progress still there are so many problems which have not yet been fully solved in celestial mechanics and it is expected that planetary as well as lunar and satellite motion theories will be further improved. This report does not cover all the papers published or works done in 1979-1981. Unfortunately, the sections on periodic solutions and on mathematical theories had to be made very short and those on natural and artificial satellite theories had to be dropped because of 12 page limitation of the report of the commission. However, please refer the natural satellite theories to the report of Commission 20. II

PLANETARY THEORY

At the Bureau des Longitudes new planetary theories have been developed by two different approaches(25.042.073), namely, by the method of successive approximation and the iterative method. In both cases solutions are put in quasi-periodic functions of time, namely, they are developed into trigonometric series, for which the arguments are linear combinations of the mean longitudes of the eight planets and the coefficients are numerically expressed by polynomials of time. 21

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By the method of successive approximation perturbations are developed formally in powers of planetary masses by starting from Keplerian orbits and Lagrange planetary equations. The first-order solutions were obtained and published in 1975. Second-order theories are derived for the major planets and the four inner planets, respectively, by Simon and Bretagnon(22.042.04l and 006) and Bretagnon(27.042.057). The aimed accuracies are 0."001 for the inner planets and 0."01 for the major planets after a century. However, comparisons with numerical integrations show that it is 0."01 for the inner planets. Third-order perturbations have been already derived by Simon and Francou and their paper is in the process of publication. By the iterative method the successive solutions of Lagrange planetary equations are obtained by Fourier series manipulations. This method is applied to the major planets. Six iterations are necessary for some cases, particularly for Jupiter-Saturn interaction calculations. Althogh this method has a disadvantage in computing quasiresonant terms with satisfactory accuracy, the solutions converge at the level of 0."001 for short-periodic terms and that of 0."01 to 0."1 for long-periodic terms. Comparisons with the numerical integrations by Oesterwinter and Cohen(1972) could determine the orbital constants. The comparison shows that except for very longperiod terms in the longitudes of Uranus and Neptune estimated errors in the theories are about 0."3 in the mean longitude and 0."1 in other elements after 1 000 years( Bretagnon, A & A lOl p342 1981). For the inner planets, on the other hand, the comparisons for 25 years give the following accuracies: 0."005 for Mercury, 0."003 for Venus and the earth and 0."005 for Mars. This represents an improvement of a factor 10 to 100 over the theories by Le Verrier and Newcomb. A method to construct planetary theory that does not allow for any periodic term with time-dependent amplitude is developed by Duriez(25.042.l00). This method is applied to the four outer planets up to the second order of the masses and to the seventh degree of the eccentricities and the inclinations. Comparisons with numerical integrations and the theory by Bretagnon show that the secular mean variations of the angular orbital elements are derived with the accuracy of 0."1 per year. Brumberg(22.042.087) proposes a new method to treat perturbed two-body problem in rectangular coordinates. The method is based on reduction of the variational equations of the two-body problem with arbitrary elements of the Jordan system. Pavlov(26.042.028) derives an expression of the coordinates of a planet through the eccentric anomaly of a disturbing planet. Krasinsky, Pitjeva, Sveshnikov and Sveshnikova develop an analytical theory of the motion of the inner planets and compare them with Venus radar observations. Its brief description is given in 22. 091.071. Pitjeva(27.092.00l) improves the orbital elements of Mercury necessary for the analytical theory by using radar observations in 1964-1965. Kamel and his colleagues are developing a general planetary theory and study the. motions of Uranus and Neptune(25.04l.l05, 26.042.001 and Ap & Space Sc 78 p3 1981). Perturbations by Pluto in the other planet motions are evaluated by Piraux(26. 091.017). New methods to expand the disturbing function for Pluto-Neptune interactions are devised by Petrovskaya and Ivanova(22.042.l22) and Yuasa and Hori(25. 042.074). They claim that the convergency for this case is satisfactory by their method. Mayo(25.098.069) derives analytical expressions for the perturbations of planetary orbits due to a thick constant density asteroid belt. Lestrade(A & A lOO p143 1981) derives analytical formulas for relativistic corrections in planetary orbits, which give not only secular perturbations but also periodic terms, one of them having 9km amplitude for Mercury. Anatonacopoulos and Tsoupakis(25.066.245) derive expressions of a second-order post-Newtonian approximation for N-body system and improve the formula for the secular motion of the perihelion. Anatonacopoulos(25.066.246) derives the equations of motion for a test particle near one of the triangular points in the field of a heavy body up to second post-Newtonian approximation. Piragas, Zhdanov, Aleksandrov and Piragas(22.066.07n treat a test particle motion in the centrally symmetric gravitational field of general relativity. They claim that the form of the equations and the main results

CELESTIAL MECHANICS

23

remain valid in the two-body problem of comparable mass in the post-Newtonian approximation. Hiscock and Lindblom(2s.042.l3s) report that the post-Newtonian secular motions of the pericenters of the innermost satellites of Jupiter and Saturn are largest in the solar system, being many times larger than that of Mercury. Brumberg (26.042.035) derives relativistic ephemeris corrections in radar ranging measurements and astrometric observations of inner planets for the case that the earth and one of the inner planets move along circular orbits on a same plane in the solar gravity field described by the generalized three parametric Schwarzschild metric. Comparisons between existing theories and numerical integrations are also made by several authors. Comparisons between Newcomb's theory and JPL-ephemerides for the earth-moon system are made by Stumpff(A & A lOl ps2 1981) for 1700-2100. When Newcomb's theory is corrected the residuals are reduced to 0."05 for the 400 years by changing the adopted constants. Kinoshita and Nakai(2s.097.048) report that the largest discrepancy between Clemence's theory of Mars and their numerical integrations is 0."054 and reformulate the theory by the same way as Clemence and correct some errors. After that the largest difference is reduced to 0."025 in longitude. Numerical theories of Mars for 1961-1972 and those of the major planets in 19502150 are developed by Izvekov(2s.097.048 and 27.092.001) and Dolgachev, Domozhilova and Rybakov(2s.09l.009 and 26.091.028). Izvekov(27.09l.002 and 27.093.018) claims that Venus motion is known with the accuracy of 10-9 AU for 1961-1972. At US Naval Observatory planetary ephemerides using the IAU 1976 system of astronomical constants and the equator and the equinox of the FKs(J2000.0) are developed by Kaplan, Pulkkinen, Satoro, Van Flandern and Seidelmann with cooperation of Standish and Williams of JPL and Oesterwinter. They find that there are still some systematic differences between the observations and the ephemerides for some of the outer planets. One of the hypotheses being investigated is existing of another planet beyond Pluto. Efforts are made to express coordinates of planets with Tchebyshev polynomials of time by Rocher(27.098.0l4), by Chapront and Rocher(27.042. 092), by Khotimskaya(27.09l.024) and by Doggett. III

LUNAR THEORY

The main incentive for developing a more accurate theory of the motion of the moon is the fact that lunar laser ranging observations have achieved now a few ce~ timeter accuracy and in order to interpret these observations any theory which is able to represent the motion of the center of the mass of the moon with the same accuracy must be in hands. Presently only numerical integrations can provide lunar positions with such a high internal consistency. The last two such integrations available are DE-Ill of JPL and ECT-18 of CERGA and the University of Texas. Both have been used for the reduction of the lunar laser ranging data. Therefore, several authors have been trying to improve the solutions of the main problem and the expressions due to the shapes of the moon and the earth. Although the solar perturbations are, of course, much larger than any others, many people have suspected that the planetary perturbations in Brown's theory have many errors and, therefore, the weak point in the exis~ing theories is rather in this part. One of the existing theories which are used for calculating the lunar ephemeris was formulated by Eckert and Bellesheim by the same principle as Brown and is called ELE. Gutzwiller (25.094.076) compares ELE with two new theories, ALE by Deprit and SALE by Henrard. About 200 largest terms in each of the polar coordinates are used for comparisons. With a few exceptions the differences are below 0."001 for the longitude and latitude and 0."000 01 for the parallax. ELE is further improved by Vondrak(2s.094.062). Literal solutions of the main problem is derived by Schmidt(2s.042.062 and 27. 042.035) with use of a computor manipulation method by the same way as Hill and Brown. Lestrade(28.042.06s) applies Laplace's idea to use the true anomaly as the independent variable to the lunar theory. A purely analytical approach to solve

24

COMMISSION 7

the equation is made by expressing the solutions in formal power series of the three parameters, namely the ratio of the solar and lunar mean motions, the eccentricity and the inclination. The difficulty arises from the fact that the expansion converges only very slowly and only modern high-speed computors can scope with the huge developments involved that have to be made at least to an order of 25 to 30 in the ratio and also a very high degree of the eccentricity and the inclination. The formal convergence of such a theory is investigated by Bec-Bosenberger(26.094.0l9) and Kovalevsky(26.094.033) and it is shown that despite the possible presence of small divisors of order 3 it is possible to gain one order more in the accuracy of the solution with a finite number of iterations. Dong(27.042.088) proposes a method to derive an exact solution of Hill's equation and discusses its convergency and its connection to Floquet solutions. Brown and Eckert give a numerical value to the ratio of the mean motions and solve the equations of motion. However, it is easier to give their approximate numerical values to all the parameters and then to solve the equations, and in order to adjust the values by fitting the observations and to obtain the solutions corresponding to their adjusted values partial derivatives of the solutions with respect to the parameters are computed. Solutions of this type are derived by ChaprontTouze(27.094.005) at the Bureau des Longitudes and is called ELP. Henrard at Namur adopts a little different method to derive the solutions. At first he derives a solution of the main problem in an analytical way by giving very good numerical values to the parameters. And then he expands the solutions around the nominal values for the parameters and solves the main problem(25.094.075). Therefore, his parameters, in powers of which the solutions are expanded, are the increments to the nominal values. His solution is called SALE. The two authors, Chapront-Touze and Henrard, (27.094.042) compare their results with each other. The conclusions are that ELP seems to be more precise while SALE seems to be more complete and precise as far as derivatives with respect to the orbital parameters are concerned. The differences are 0."000 94(200cm) in longitude, 0."00023(45cm) in latitude and l20cm in distance, and, therefore, are much larger than their anticipated errors, particularly for the distance. Kinoshita compares the two theories with his numerical integrations for 13 revolution period and finds that the differences in the lunar distance are 100cm for SALE and 1.2cm for ELP. Even after 20 years the difference is as small as 1.5cm for ELP. Referring to the planetary perturbations Vondrak(25.094.006) reformulates the expressions by Brown's procedure and finds some mistakes in Brown's formulas. And he derives several small terms which were neglected by Brown and publishes a list of the planetary terms. Standaert(28.09l.037) computes analytical expressions of the direct planetary perturbations by Lie method using Henrard's solution(SALE) and Bretagnon's planetary theorie~. The accuracy intended is 0."001 for terms of period up to 2 000 years. Chapront-Touze and Chapront(28.094.030) compute both direct and indirect planetary perturbations in the frame of ELP. Differences between their solutions and Brown's are as large as 0."005. Common parts of the two solutions by Standaert and Chapront-Touze and Chapront are compared with each other and it is found that the discrepancies of the values of the coefficients are smaller than 0."000 2. The perturbations due to the second harmonics of the geopotential, the nutation and the secular variations of the obliquity are computed by Chapront-Touze and compare satisfactorily with similar computations by Henrard. The perturbations due to the shape of the moon are also romputed with the accuracy of 0."000 01 in longitude and latitude and 5 parts in 10 1 in distance(28.094.036). Relativistic effects and those due to the tides are also computed at the Bureau des Longitudes and Namur, respectively. ELP, more exactly ELP 2000 which is computed by the astronomical constants at 2000, is compared with the numerical integrations by Williams(LE5l) after including all the perturbations and it is found that the maximum discrepancies are 20m in longitude and 12m in distance. However, even with such an accuracy it is

CELESTIAL MECHANICS

25

100 times better than that of the current ephemerides such as ILE used in almanacs. ELP will be introduced in the Connaissance des Temps. IV

ROTATIONAL MOTION

New theories of the rotation also have been anticipated for the moon to match with the increased accuracy of the lunar laser ranging observations. In fact Eckhardt(Moon & Planet 25 p3 1981) revises his theory by using more precise models for the gravity potential, the revolution motion and the interior of the moon. Tables which are based on his theory and are truncated at 0."01, are published. Migus(28.094.04l) and Moons(Thesis, 1981) also develop their theories. The largest differences among the three theories over several year interval are 0."25. Yoder (26.094.036) improves the rotation theory by adding the torque exerted by an oblate earth, the effect of which is 0."08 in latitude, and by adopting a non-rigid viscous moon model. Cappallo, King, Counselman and Shapiro(Moon & Planet 24 p28l 1981) integrate numerically the equations for the rotation of the moon with revised values for the parameters after determining the initial conditions by fitting the integrations with lunar laser ranging observations at McDonald Observatory with 28cm rms residuals. The results are compared with the numerical theory by Williams(1975) and the theory by Eckhardt (1981) , their rms differences in orientation being 0."03 and 0."2, respectively, after removing constant biases. Markov(27.094.036) derives solutions by applying Poincare's periodic solution theory and by expressing them with osculating elements of Andoyer. Barkin(25.042.003) discusses the stabilty of the solution for the real rotation motion near the periodic solution according to Cassini's law. The rotation of Mercury and its stability are dicussed by Burns(25.092.009) by taking into account the solar tidal bulge and the solar torque on the permanent tide. For Venus its dynamical evolution is discussed by Beletskij, Levin and Pogorelov (26.093.143, 27.093.016 and A Zh 85 p198 and p4l6 1981) by taking into account the torques by the sun and the earth and Lago and Cazenave(26.093.028) investigate the past evolution of the rotation by taking into account the solar tidal torque and mantle-core coupling and show that a thermally driven atmospheric tidal torque can drive the obliquity from a small value to 180° which corresponds to a stable position. Variations of the rotation rate, the nutation and the precession for Mars are discussed by Borderies and Balmino(25.097.049), by Reasenberg and King(26.097. 082), by Borderies, Balmino, Cagtel and Moynot(27.097.06l) and by Borderies(27.097. 006). Ward(25.097.003) derives the oscillation motion of the obliquity of Mars by using expressions correct up to the fourth degree of the eccentricity and the inclination and an improved value of the moment of inertia and by a linearized theory predicts that the maximum oscillation amplitude is 13.°6 and the center of the oscillation is 24.°4 in the long-term average. Zhang(27.l07.024) obtains primitive periods of the nine planets and its averaged value for asteroids by assuming that all planetesimals and particles were revolving around the sun in circular orbits. Beletskij(Cel Mech 23 p37l 1981) studies how the rotation rate and the inclination of protoplanet had been changed during the first stage of protoplanet formation. Khentov's analysis(22.042.lll) on stability conditions of the rotation of planets and satellites discloses why spinorbit synchronism has not been realized for most of the celestial bodies. Murdock (22.042.072) and Murdock and Robinson(CeZ Mech 24 p83 1981) study some mathematical aspects of spin-orbit resonances. Bursa(27.042.04l and 043) derives components of the resulting moment of external gravitational forces caused by a general body and discusses Liouville's equation describing the rotational motion of deformable celestial bodies. It is not intended to include here the rotational motion of the earth.

26

COMMISSION 7

V DYNAMICAL EVOLUTION AND STABILITY a)

General Theory and Planets

Many papers for explaining the present distributions of satellites, asteroids, rings and comets and their dynamical evolutions appeared. For satellites tidal dissipations and planetary encounters may be the most important factors and for comets capture processes by planetary encounters are mostly discussed. Narrow rings which were discovered for the three planets attract much attentions and there are alternative theories for their origins. Duriez(22.042.010) proves that a secular term of the third order of masses appears in each expression of the semi-major axis of the planets. Barricelli and Aashamar(27.107.023) test by computor simulations whether successive captures followed by planetary fusion could lead to the formation of major planets comparable to Jupiter and Saturn. Yoder(25.041.013) analyzes orbit-orbit and spin-orbit gravitaional resonances using the model of a rigid pendulum subject to a periodic and a constant torques and derives a probability for capture into libration. H[meenAntilla and Lukkari(26.042.038) show that the decrease of the orbital inclination of a planetesimal stops when its rms distance from the equatorial plane is twice its radius. Zhou(26 .042 .015) discusses the two cases .of .thethr:ee...,bo.dy>problerg, namely sun-Jupiter-Saturn and sun-Neptune-Pluto cases, and computes the regions of the variations of their orbital inclinations. Carussi and Pozzi(22.042.082 and 083) develop a new method for close encounter computations and investigate close encounters between Jupiter and 3 000 fictitious minor bodies. b)

Moon and Satellites

Szebehely and Evans(27.094.006) study a possibility of the lunar capture by assuming that the mass of the sun had been decreased in an early stage and conclude that 38% mass decrease is necessary. Mignard(25.094.067 and 28.094.018) derives a simple equation for studying the tidal evolution of the lunar orbit, discusses qualitative properties of the solutions, integrates it numerically and shows how the inclination and the eccentricity had changed during the close approach to the earth. Lambeck and Pullan(27.094.060) rediscuss the time scale of the lunar evolution as a function of the shape of the moon. Grjebine and Marchal(27.094.030 and 031) argue in favor of a fission hypothesis of the origin of the moon and suggest that the moon stayed for a long interval of time in a geostationary orbit. Many people believe that Phobos and Deimos, the Martian satellites, were carbonaceous asteroids captured by Mars. Hunten(25.097.007) suggest that the capture took place due to the drag of an extended proto-atmosphere and Van Flandern(26.097. 180) adds that collisional and tidal forces could evolve the captured satellites to their present orbits in a sufficiently short time. Lambeck(26.097.031) investigates tidal evolution of the satellites and shows that the tides raised by the planet on them have significant consequences. Cazenave, Dobrovolskie and Lago(27.097.005 and Icarus 44 p218 1981) show that the Martian satellites could have been captured in Mars's orbital plane and later evolved to their present planes as the tidal effects moved the orbits. Mignard(MNRAS 194 p365 1981) discusses ·the tidal evolution of the Martian satellites for a frequency dependent model of the tidal lag for the planet and the satellites and computes the solutions by starting from the presently observed secular accelerations. Many people are convinced that the tidal dissipation is an important factor for the evolution of Galilean satellites of Jupiter. Peale, Cas sen and Reynolds (25.099.003) try to explain the volcanic activities on the surface of 10 by the fact that the dissipation of tqe tidal energy in it is likely to have melted a major fraction of the mass. Yoder(25.097.047) makes a similar argument and discusses how the tidal dissipation in 10 and Jupiter controls the resonant configuration among the three inner satellites. Cassen, Reynolds and Peale(Geophys Res L

CELESTIAL MECHANICS

27

6 p73l and 7 p987 1980 and Icarus 4l p232 1980) argue that it is possible for the tidal dissipation in the crust on Europa to have preserved a liquid water and report that the tidal dissipation could not have been important for Ganymede for more than 10 8 years and it was never important for Callisto for the formation of the surface. Greenberg(Icarus 46 p4l5 1981) treats the tidal evolution of the Galilean satellites in a linearized nine dimensional system of equations, studies small variations around its equilibrium solutions and derivffia conclusion in favor of his deep resonance origin hypothesis. Greenberg(in Satellites of Jupiter 1981) shows that the orbital motions of the Galilean satellites exert dramatic control over their physical properties through the tidal heating and in turn the tidal dissipation in the satellites and Jupiter has governed the evolution of the orbits and the Laplace resonance relation. Wiesel(AJ 86 p6ll 1981) discusses the problem of the creation and subsequent evolution of the great resonance of the three Galilean satellites by using a periodic solution and shows by numerical integrations that the resonant state can be directly entered under the influence of the tidal forces without prior formation of individual 2:1 resonance pairs. Peale, Cassen and Reynolds(28.l00.0l8) argue how eccentricities of Saturnian satellites were decreased by the tidal dissipation and estimate the rigidities and the dissipation function. Peale(22.l00.5l2) discusses that finding Hyperion rotating in the 3:2 spin-orbit resonance like Mercury would imply a primordial origin for the Titan-Hyperion resonance. Bevilacqua, Mench, Milani, Nobili and Farinella (27.100.048) study the resonant case of Titan-Hyperion by numerical integrations, find invariant curves corresponding to low and high eccentricity resonance lockings and show that the observed libration of Hyperion's pericenter lies inside the stable high eccentricity region. Blitzer and Anderson(Cel Mech 29 p65 1981) investigate a theory of satellite orbit-orbit r~sonance which is applicable to Titan-Hyperion and Mimas-Tethys pairs. Dermott and Murray(Icarus 1981) discuss the properties of the tadpole and horseshoe orbits of the restricted problem of three bodies using analytical and numerical methods, determine the circumstances in which the horseshoe paths rather than the others are expected, and apply their results to the recently discovered co-orbital satellites of Saturn which are shown to be librating in horseshoe orbits. Dermott(25.09l.006) computes the present rate of the energy dissipation for Jupiter and Saturn under the assumption that the orbital resonances of their satellites are the results of the orbital evolution due to the tidal dissipation and mentions that approximately the same value is needed for the dissipation factor for all the major planets for such evolutions in spite of the great difference of the energy dissipation rate by the factor greater than 10 4 • Harrington and Van Flandern(25.l0l.025) show how Pluto and the satellites of Neptune have been originated from a single encounter of Neptune with a massive body. Dormand and Woolfson(28.l0l.002) argue that Pluto was ejected from Neptune system by an encounter with Triton. Mignard(A & A 96 pLl 1981) favors the idea that Charon was separated from Pluto by a fission process when it was ejected from the Neptune system as Charon is likely tidally locked and the total angular momentum of the system is similar to the one required for a rotational break-up of a fluid body. Several mathematical papers on the evolution also appeared. Szebehely and McKenzie(22.052.034) compare the results obtained by three methods for stability on satellite motions and derive the simplest formula for the most conservative condition. Dovrak and Marchal(22.042.048) make a simple qualitative analysis of the perturbations on a satellite to derive a lower bound for the duration of escape or capture of a satellite and conclude that it rules out any escape for at least 21 centuries for any satellite. Cline(25.042.084) makes a two-body patched conic analysis for a planetary capture of satellites, in which a gravity assist by a satellite aids in capture. Tanikawa(25.099.058) considers a slow capture process, in which particles approaching the planet lose their energies gradually and fall down into stable orbits around it.

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Rings

Arguments how Uranian rings were formed are made in several papers. Steigmann (22.101.002 and 25.101.002) suggests that the radii of the a and y rings of Uranus and perhaps Eland 2 are governed by the resonance with Miranda and Ariel, however, Sand 8 rings might be associated with an undiscovered satellite with mass equal to 0.4 Miranda's mass. Goldreich and Tremaine(25.l0l.00l and 26.101.024) suggest that inter-particle collision, radiation drag and differential precession tend to disrupt the rings of Uranus and propose that the rings are confined by gravitational torques from a series of small satellites that orbit within the ring. They suggest that the apse alignment is maintained by the self-gravity. Dermott, Gold and Sinclair(26.l0l. 001) suggest that orbital resonances are involved for the formation of extremely narrow widths and sharply defined edges of Uranian rings and suppose that each ring contains a small satellite which maintains particles in horseshoe orbits around the triangular points. Dermott, Gold and Sinclair(27.099.006) also make a similar argument for narrow rings of Jupiter and Saturn and attempt to account for the origin and the location of the rings. Dermott and Murray(28.l0l.035) criticize the argument that the apse alignment of the eccentric E ring is maintained by the self-gravity alone, consider that it is the close packing of the particles near the pericenters which prevents differential precession and describe how differential precession, particle collisions and self-gravitation together can transform a narrow eccentric ring of uniform width into a ring with a large, positive eccentric gradient. Dermott(Nature 290 p454 19 81) explains the braided appearance of the F-ring of Saturn by an excited wave pattern of equally spaced loops which co-rotate with one of the shepherding satellites of the ring which has one first-order resonance with the ring. Zhou and Zheng(28. 042.005) make numerical simulations for a system of colliding bodies to explain a formation of rings. Cuzzi, Burns, Durisen and Hamil(Nature 28l p202 1979 and 26.100.034) discuss the vertical structure and thickness of Saturnian rings and describe how solar and satellite perturbations do no significantly affect the vertical thickness but do affect the tilt of the mean ring plane. Henon(Nature 293 p33 1981) describes a very simple model of Saturnian rings based on the assumption that the size distribution of particles in the rings is uniform with no preferred value. d)

Asteroids

Yoder(26.098.073) points out that the tightly bound population of Trojan asteroids has secularly evolved from less to more tightly bound orbit configuration through some mechanisms including the changes of the Jovian mass or semi-major axis during planetary formation and collisional interactions with external bodies. Bien (22.042.011, 27.042.004 and 27.098.074) derives a solution for Trojans as an example of planar elliptic three-body problem and follows orbits of 18 Trojans with small inclinations and also those with high inclinations. Garfinkel(22.042.075 and 28. 042.040) constructs a formal long-periodic solution for Trojan asteroids in the restricted three-body problem and discusses its properties. Erdi(22.042.06l, 26.098. 004 and Gel Mech 24 p377 1981) considers the motion of Trojan asteroids using a three-variable expansion method for the elliptical three-body problem, derives an asymptotic solution, conditions for the lib ration of the perihelion and the periods of variations of the eccentricity and finds that for 20 of 30 cases the perihelion longitudes circulate and for the others they librate. Then Erdi and Presler(28.042. 171) test the theory with numerical integrations and find that the periodicity of the eccentricity is about 3 600 years. Froeschle and Scholl(25.098.004) make numerical integrations over 10 5 years of fictitious asteroids in the region of 3.6 to 3.9AU and show that a partial depletion of an initially uniform distribution is possible by close encounters with Jupiter. However, Franklin(26.098.07l) reports that the truncation outward from 3.4AU of asteroids cannot be strictly the results of perturbations of major planets even over

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10 9 years and sets the limit of 0.081 for Jupiter's eccentricity for the stable motions of outer asteroids. Dermott and Murray(Nature 290 p664 1981) apply statistical techniques to asteroid orbital data and find that the eccentricity and the inclination increase away from the gaps. They argue that the process responsible for the formation of the gaps has removed those objects near the resonances as there is no significant tendency for low-magnitude objects near the gaps which rejects the collisonal hypothesis of the origin. Froeschle and Scholl(25.098.06l) report that the resonances generally tend to enhance eccentricities and inclinations. Heppenheimer(22.l07.0l4 and 28.042.142) derives conditions for growth of planetesimals in the presence of thirdbody perturbations and proposes that the gaps are primordial and correspond to region where asteroids failed to form by creation. Gulak(27.09l.00l) considers that commensurability is a result of dynamical relaxations of spatially restricted mechanical systems with an attracting non-point center. Zhuravlev(27.098.022) concludes by numerical integrations that an observed asymmetry of the gaps relative to the exact commensurability is due to a resonant interaction of asteroids with Jupiter. Arazov and Gaibov(26.097.005) construct an intermediate orbit for resonant asteroids on the basis of a solution of the internal variant of the generalized three fixed center problem and apply it to 2:1 case. Franklin, Lecar, Lin and Papaloizou (27.098.135) study numerically and analytically the conditions for the truncation at the 2:1 resonance of a disk of infrequently colliding particles surrounding the primary of a binary system and conclude that the truncation and the gaps were produced only if the eccentricity is less than some critical value around 0.08. Dirkis (22.098.009) studies the motion of asteroids near 2:1 resonance by numerical integrations over 2 000 years. Simonenko, Sherbaum and Kruchinenko(26.098.072 and 26. 042.046) study the orbital evolution for asteroids near 3:1 resonance by a model calculation for 500 years and derive the condition for libration. Karminskij(26. 098.050) studies the real asteroids with 3:1 mean motions. Danielsson(22.098.042) computes for 1 200 years Toro's orbit which is in resonance with the earth and Venus. Scholl(26.098.074) integrates numerically Chiron's orbit from 6 OOOBC to 18 OOOAD and supports the conjecture that the dynamical evolution of Chiron is similar to those of short-periodic comets. Heppenheimer(27.l07. 003) treats a mechanism for the origin of the eccentricites of asteroids and that of Mars by secular resonance associated with the dissipation of a primitive solar nebula. Williams and Faulkner(Iearus 46 p390 1981) derive positions of secular resonance surfaces as a function of proper semi-major axis, eccentricity and inclination. Kozai(27.098.003) lists the names of the numbered asteroids for which the eccentricities and the inclinations are changed very much by the secular perturbations. Gradie, Chapman and Williams(27.098.038) and Kozai(27.098.037) restudy the families of asteroids. Simovljevitch(26.042.034) introduces the concept of regular proximity of two asteroids and Lazovic lays out a simple method to determine approximate true anomalies of proximity of two elliptic orbits for small minimum distance case(22.042.ll3). e)

Comets

Yabushita(25.l02.004) studies the effect of planetary perturbations on longperiodic comets and shows how the distribution of the binding energies of comets varies with time. Nakamura(Iearus 45 p529 1981) computes the orbital evolution of long-periodic comets to short-periodic ones for 16 representative initial orbits and finds that survival rates of the initial orbits with high inclinations and small perihelion distances are only two or three times smaller than those of the main source orbits. Tomanov(28.l02.004) by considering interaction of parabolic comets with Jupiter shows that short-periodic comets must have only direct motions and the deficiency of comets with the semi-major axes of 20 to 30AU is explained by the small probability of capture. Rickman and Froeschle(26.l02.03l, 27.102.027 and 008) introduce a fast method to study the orbital evolution of active comets in the inner

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planetary region and conclude that for each active Mars-crossing comet there are 50 distinct comets on similar orbits. Froeschle and Rickman(Iaarus 46 p400 1981) derive statistical distributions of Jovian perturbations on short-periodic comets by making numerical integrations with sample of 60 000 comets with low inclinations, perihelion distances between 0 and 7AU and aphelion between 4 and l3AU. Carussi and Valsecchi(A & A 94 p226 1981) make a numerical research on dynamics of close approaches of short-periodic comets with Jupiter and confirms that in several cases objects can be captured by the planet as temporary satellites. Carussi, Kresak and Valsecchi(A & A 99 p262 1981) make a numerical computation of a chain of 80 objects placed along an arc of the pre-encounter orbit of P/Oterma and show that close encounters produce a broad variety of jovicentric and heliocentric orbits including temporary captures by Jupiter over 100 years. Rickman and Malmort(A & A l02 p165 1981) discuss a possibility of temporary capture of P/Gehrels 3 by Jupiter. Vsekhsvyatskij and Guliev(A Zh 58 p630 1981) estimate that there are comets which were escaped from the system of Uranus. VI a)

SOLUTIONS AND THEIR PROPERTIES OF DYNAMICAL SYSTEMS

Periodia Solutions of Three-Body Problem

Many new families of periodic solutions of the three-body problem are found theoretically and numerically by extending the known solutions usually from bifurcation orbits which are also derived. The extension is made from planar restricted problem to three-dimensional and to the general problems. Families of periodic solutions for the sun-Jupiter case are followed by this way. Kazantzis(22.042.l02) first investigates basic families of plane symmetric orbits for restricted problems and studies their horizontal and vertical stabilities and Kazantzis and Zagouras(25.042.l06) investigate numerically the bifurcation orbits. Then Kazantzis (25.042.051 and 053, 26.042.040 and 27.042.071) finds new families of three-dimensional periodic orbits with simple and double symmetries of restricted and general problems starting from vertical critical orbits. Zagouras and Kazantzis (25.042.052) derive three-dimensional periodic oscillations about collinear equilibrium points. Robin and Markellos(27.042.046) derive three-dimensional satellite periodic orbits by a similar way. Kasperczuk(26.042.063) and Bien(27.042.034) treat periodic solutions for the sun-Jupiter case. Michalodimitrakis(25.042.058 and Ap &Spaae Sa 78 p27 1981) investigates doubly symmetric vertical critical periodic orbits of Copenhagen problem and finds new families of three-dimensional orbits for the general problem. Ichtiaroglou, Katopodis and Michalodimitrakis(22.042.078,28.042.049 and 066) extend periodic orbits of Copenhagen problem, to restricted planar and then to general problems. Michalodimitrakis (25.042.061, 26.042.039 and 27.042.003) and Itchtiaroglou(27.042.002 and 017 and 28. 042.032) derive mono- and bi-parametric families of symmetric three-dimensional periodic orbits and Markellos(22.042.004 and 27.042.038) computes three-dimensional periodic orbits which contain asymmetric ones for restricted and general problems. Also Katopodis(25.042.0l5) extends periodic solutions in the three-dimension from restricted to general problems. Ichtiaroglou(27.042.002) proves the existence of families of vertical critical periodic orbits of the general planar problem. Robin(Cel Meah 23 p97 1981) discusses bifurcation of plane with three-dimensional periodic orbits in the elliptic restricted problem and Markellos(Cel Meah 25 p195 1981) treats the same problem for the general problem. Belbruno(Cel Meah 25 p195 1981) studies a new family of three-dimensional periodic orbits for the restricted problem which continue off from a consecutive collision orbit. Brjuno(22.042.057 and 058) derives periodic solutions for the restricted problem with consecutive collisions. Markellos and Taylor(22.042.085) derive asymmetric periodic and asymptotic orbits for the restricted problem. Marchal(25.042.085) investigates periodic solutions with very long periods for the general problem.

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31

Henrard(27.042.030) and Message(27.042.027) prove the existence of Poincare's periodic orbits of second species and sort, respectively, in the general problem. Ishwar(25.042.001) treats periodic solutions of second genus in the plane restricted problem. A conjecture of Poincare on the density of periodic orbits of the restricted problem is studied by GOmez and L1ibre(Cel Meeh 24 p335 1981). Periodic orbits of Hill's problem in its more general cases are treated by Breakwe1l and Brown(26. 042.038), Micha1odimitrakis(27.042.0l8), Ichtiaroglou(28.042.064 and A & A 98 p401 1981) and Latyshev(28.042.045). Henon is studying the evolution of the periodic orbits in the restricted problem when the ratio of the masses tends to zero. Sharma (Ap &Space Se 76 p255 1981) derives periodic orbits for the case that the more massive primary is an oblate spheroid for the restricted problem. c)

Equilibrium Points of Three-Body Problem

Stabilities of equilibrium points of the three-body problem and periodic orbits around them are also discussed in several papers. Duboshin(25.042.060) investigates solutions of Lagrange and Euler in the general problem in absolute coordinates. The stability of the triangular points for the elliptic restricted problem is discussed by Ivanov, Karimov and Sokol'skij(28.042.016) , Meire(28.042.021 and Cel Meeh 23 p89 1981) and motion near the points is discussed by Cheng(25.042.014). The stability of the point for the circular restricted problem is treated by Sokol'skij(25.042.054). Ivanov(26.042.024) discusses the stability in non-restricted problem and McKenzie and Szebehe1y(Cel Meeh 23 p223 1981) investigate non-linear stability around the point. Mitt1eman(27.042.070) treats motions about this point for the restricted problem. Bhatnagar and Ha11an(22.042.059 and 26.042.006) investigate effects of the perturbations in Corio lis and centrifugal forces on the stability in the restricted problem. Szebehe1y and McKenzie(Cel Meeh 23 p131 1981) study deformation of a line element in the phase space at the point. Van Ve1sen(Cel Meeh 23 p383 1981) studies isoenergetic families of quasi-periodic solutions near the point and Broucke(25.042. 040) discusses isosceles triangular configurations in the planar general problem. Pue1(26.042.007), Broucke and Wa1ker(27.042.029), Broucke. Anderson. Blitzer. Davoust and Lass (Cel Meeh 24 p63 1981) and Richardson (28.042.036 and 038) study rectlinear problems of the three-body system, periodic orbits about the collinear equilibrium points, rect1inear isosceles orbits and related topics. d)

Triple Collisions in the Three-Body Problem and Systems Including Finite Bodies

Losco(22.042.030), Wa1dvoge1(25.042.027), Irigoyen(26.042.030 and 031 and 28. 042.001), Marchal and Losco(27.042.040),Sim6(27.042.023) and Eschbach(27.042.039) investigate triple collisions in the three-body problem by deriving new systems of equations, studying triple collision manifolds and finding orbits near the collision including triparabo1ic escape orbits. Duboshin(22.042.036 and 28.042.018), Troitskaya(27.042.013), Kondurar' and Gamarnik(27.042.059), Vidyakin(27.042.016)andIpatov (28.042.075) study trans1atoryrotational motions of three or two rigid bodies in the three-body problem. Eh1'Sharburi(22.042.110), Jezewski and Dona1dson(25.042.016), Sid1ichovsky(28.042.020 and 037) and Vidyakin(28.042.047) study translatory-rotational motions of two rigid triaxial or axisymmetric bodies. Ste11macher(26.042.154 and Cel Meeh 23 p145 1981) studies periodic orbits around an oblate spheroid. Barkin(25.042.056), Barkin and E1-Sharburi(25.042.006) and Abu1'naga and Barkin(26.042.002) investigate motions of a rigid body in the attraction of a sphere. e)

Several Aspects of Three-Body Problem

Stability for satellite case is investigated by Wi11iams(25.042.082), Marke110s and Szebehe1y(Cel Meeh 23 p269 1981), Markel10s and Roy(Cel Meeh 24 p183 1981) and Marchal and Bozis. Chen, Sun and Luo(22.042.092) and Sun and Luo(28.042.004) analyze the range of the orbital inclinations with respect to the invariable plane for the general problem. Nezhinskij(27.042.080) and Hu1kower(27.042.024) study central configurations. Kammeyer(28.042.04l) studies linearized mapping associated with the

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planar problem near a periodic orbit. Chen(22.042.00l) discusses the topology of the manifold of the general problem and Nahon(25.042.067) studies collision orbits. Luk'yanov(22.042.050), Ziglin(22.042.l2l), Aksenov(25.042.045 and 055), Delmas (25.042.053), Matas(25.042.0l0), Timoshkova(25.042.007), Delva and Dvorak(26.042.0l2), Vrcelj(26.042.0l0) , Innanen(27.042.005), Radzievski(27.042.058), Veres(27.042.008), Sokolovand Kholshevnikov(27.042.006 and 069), Waldvogel(27.042.036), Hitzel and Levinson(28.042.007), Veres(28.042.046), Wisdom(28.042.002), Zhuravlev(28.042.014), Degraeve and Pascal(Cel Mech 24 p53 1981), Gonczi and Froeschle(Cel Mech 25 p271 19 81), Langebarte(Ap & Space Sc 75 p437 1981), Pascal(Cel Mech 24 p53 1981) and many other people investigate several aspects of the three-body problem. f)

Four and Many Body Problems

The four body problem is investigated by Simo(22.042.062) for relative equilibrium solution, by Hadjidemetriou(27.042.028) for the motion of a small body under the actions of the sun, Jupiter and Saturn, by Nash and Monaghan(28.042.006) for statistical study of disruptions, by Hadjidemetriou and Michalodimitrakis(A & A 93 p204 1981) for periodic planetary type orbits, by Michalodimitrakis(Ap & Space Sc 75 p289 1981) for circular restricted problem, by Zhuravlev and Anikovsky(Cel Mech 24 p237 1981) for expansion of the disturbing function and by Boigey(Thesis, 1981) for geometrical demonstration of the elimination of the nodes. N-body problem is investigated by Luk'yanov(22.042.l09 and 25.042.046) for symmetric solutions, by Michalodimitrakis(22.042.070 and 077) for the three-dimensional periodic solutions, by Arenstorf(22.042.035) for periodic solutions in rotating coordinates, by Lukkari(22.042.069) and Zheng and Zhou(28.042.005) for numerical simulations of colliding particles, by Marchal(Acta Astronautica 6 p123 and pl159 and 7 p555 1979) for close approaches and fundamental stability, by Devaney(25.042.083) for specific homothetic collinear solution, by Hadjidemetriou(25.042.064) for planetary type periodic orbits, by Babadzanjanz(26.042.004) for continuation of solutions, by Stellmacher(26.042.044) for the problem of N equal masses at each vertex of a regular polygon, by Saari(27.042.02l) for central configurations with collision orbits, by Walker, Emslie and Roy(28.042.058) and Walker and Roy(Cel Mech 24 p227 1981) for stability criteria, by Meyer(Cel Mech 23 p69 1981) for periodic orbits near infinity, by Smith(MNRAS 195 p35 1981) for the mean relaxation time of isolated equal mass points, by Carlberg and Hartwick(AJ 86 p14l0 1981) for a dissipationless collapse and by Marchal for possibility of regularizing singularities. g)

Other Dynamical Systems

Contopoulos and Michaelides(28.042.059) explain why the characteristics of triple periodic orbits do not bifurcate from the central characteristic. Michaelides ( 28.151.056) and Contopoulos and Zikides(28.042.033) find that a family of periodic orbits in a 1:1 resonance dynamical system has an infinity of transformations from stability to instability and vice versa. Contopoulos(Let Nuo Cimento 30 p498 1981) finds systems which do not have universal bifurcation ratio of the conservative systems. Contopoulos(26.042.06l and Cel Mech 24 p355 1981) finds that near 4:1 or more generally 2n:l resonance the central characteristic is broken into two independent families. Contopoulos, Giogilli and Galgani(26.042.064) find the evidence that there are only two quasi-isolating integrals in a system of three degrees of freedom. Then Contopoulos and Zikides(28.042.033) study periodic orbits and ergodic components of resonant dynamical system. Kazantzis(Ap & Space Sc 78 p27 1981) make numerical integrations of symmetric and asymmetric solutions for a dynamical system. Sun and Froeschle(Acta Astronomica Sinica 22 p159 1981) study dependence of Kolmogorov entropy of mappings on coordinate systems.Magnenat(26.042.0l3) examines asymptotic orbits and instability zone in dynamical systems. Losco(Cel Mech 25 p159 1981) studies the stability problem with analogy with triple collision. Y Kozai President of Commission

8. POSITIONAL ASTRONOMY (ASTRONOMIE DE POSITION) PRESIDENT: E H¢g VI-CE PRESIDENT: K N Tavastsherna ORGANIZING COMMITTEE: C A Anguita, G Billaud, S Debarbat, W Fricke, J A Hughes, B L Klock, J A Lopez, I Nikoloff, G Teleki, R H Tucker, H Yasuda, Luo Ding-jiang, Y S Yatskiv

I.

INTRODUCTION The present report covers mainly the period 1979 - June 1981.

As in the last Report, the following will contain three further sections:

II. Reports from observatories and Commission members presented under national headings. III. Other reports: from the working groups on a) astronomical refraction, b) astrolabes, and c) horizontal meridian circles. Furthermore on the d) theory of nutation, e) SRS project, and on the f) HIPPARCOS satellite. IV. Late reports. We commemorate two well-known positional astronomers deceased since the last Report: J Haas (Bonn), G K Zimmermann (Nikolayev). The following have notified their retirement from the Commission: N Hansson, J Larink, J R Levy, T Okuda, R W Rhuynsburger, A C Scheepmaker, T Tsubokawa, K Tuzi, J von der Heide. After consideration by the Organizing Committee the following will be regarded as retired from the Commission: J Gay, W Schuler, S Slaucitajs, E G Woolsey. New members according to IAU By-law 21 are: Xu Tong-qi (Shanghai), Luo Ding-jiang (Beijing), Li Dong-ming (Beijing), Hu Ning-sheng (Nanjing), Ye Shu-hua (Shanghai), L V Morrison (Herstmonceux), P T Wallace (Epping, Australia).

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II. REPORTS FROM OBSERVATORIES AND COMMISSION MEMBERS a) Australia Second epoch plates for the Perth Astrographic Catalogue Zone 31 0 to 41 0 south have been obtained to a 75% completion. For southern fields of galaxies and supporting fundamental stars in the zone of avoidance 50% of the first epoch plates have been achieved. The semiautomatic maridian circle on loan from the Hamburg Observatory has been used since completion of the SRS observing programme in 1972. Up to 1976 the FK4 and FK4 Supp. stars south of +37~5 obtained about 60 000 observations and the catalogue, Perth 75, is in press. In August 1976 observations started of 1738 reference stars for southern areas of galaxies and of 153 fundamental stars in the zone of avoidance as proposed by A N Deutsch and MS Zverev. Later, 177 suspected population II stars proposed by E H Olsen, Copenhagen, were included. The results of 360 nights are being compiled. In August 1980 an observing programme of 14702 stars set up in consultation with E H~g and E H Olsen was commenced. It contains the following stars south of +37~5: All 1156 FK4 stars in upper culmination, 75 FK4 stars in lower culmination, all further 11500 stars of mV < 7.0, 22 certain and 246 suspected radio stars, 148 pulsating variables of mV < 10, and 1801 suspected population II stars. Regular observations of the five major outer planets and the four brighter minor planets have been carried out. (I Nikoloff). At Sydney the photography of the sky from _38 030' to the South Pole has been nearly completed. The measurement of the zones centred at -63030' and _56 0 has been finished and more than half of the zone centred at -58 30'. The plates are being reduced with references from the Perth 70 catalogue. The measurements are now transferred directly from the measuring machine to the calculator and a greater output is obtained. (W H Robertson). b) Chile At Santiago the following observing programmes with the Repsold meridian circle are in progress. 651 FKSZ stars and 1217 FK4 stars are being observed with the quasi-absolute method in the zone +40 0 to _90 0 , 367 double stars and 25 galactic objects recommended by Commission 24. During the recent 2.5 years three observers obtained a total of 12 123 observations on 239 series of differential observations. A catalogue of observations of 7610 stars of the SRS and BS Programmes in the zone _25 0 to-47° is in press. Results have been presented in (25.041.046, 25.002.013, 25.041.056, and 25.041.057). (G Carrasco). Observations have been obtained with the Danjon Astrolabe (ESO/University of Chile) for a catalogue containing 358 FK4 stars and 164 FK4 Supp. stars. Uranus was observed on 107 double transits with the astrolabe. Three FK4 radio stars are being observed. (20.041.024, 25.101.013, 27.044.001, 27.012.052). (F No~!l). c) Denmark The Carlsberg Automatic Transit Circle (CATC) has been in fully automatic operation since 1981 at Brorfelde. The telescope is set automatically and the circle readings and transits are recorded using moving-slit micrometers with photoelectric detectors. The instrumental calibrations are also made automatically and observations are reduced on-line to the right ascension and declination system of the instrument. Meteorological data are recorded automatically with each

POSITIONAL ASTRONOMY

35

transit. All operations are made under the control of two computers, one of which controls the acquisition of data, whilst the other reduces and analyses these data. The instrument is capable of observing 80-90 transits an hour. A test programme of FK4 stars, polar stars, and PZT stars was started and results are promising. The instrument will be moved to La Palma during 1982 in accordance with a tripartite agreement between the observatories of Copenhagen, Herstmonceux, and San Fernando and will be run by a joint management committee. About 25% of the time will be devoted to fundamental work, which will include the FK4/5 and about 4000 other fundamental stars, the sun, the major planets and about 20 minor planets. The very first differential programmes will be limited in scope in order to demonstrate the high accuracy attainable by the instrument as soon as possible. These programmes will probably include the AGK3R and SRS, and faint reference stars in the fie~of selected radio sources. (L Helmer). Feasibility studies have been carried out of the glass meridian circle, cf. Section IIIc. Contributions were made to the realization of the ESA astrometry satellite HIPPARCOS (25.041.057, 28.032.540, 28.051.007, 28.041.040). An AngloDanish-Swedish team of scientists have been formed for the reduction of data from HIPPARCOS. Assistance was given to set up a new observing programme for Perth and to complete a catalogue Perth 75 (in press).(E H¢g). d) Federal Republic of Germany (i) At Heidelberg progress has been made in the work on the construction of the FK5. A great number of catalogues of observations have been investigated. Most of the catalogues have presented differential observations with respect to the FK4. About 35 catalogues have given results of absolute or quasi-absolute observations of FK4 stars in either both or one coordinate; these observations will yield systematic corrections to the positions and proper motions of the FK4 as functions of the position in the sky and of the magnitude. In addition, there are differential observations available which fulfill the conditions for the determination of magnitude equations of the FK4. All determinations of systematic differences (Cat-FK4) made from absolute and differential observations have been performed by means of the methods (analytical and numerical) described by Bien et al. (25.041.067). The transformation of the system of the FK4 to the FK5 will be formulated by analytical expressions developed by Schwan (publication in preparation) and tested in a pilot programme in application to all Washington 6" TC catalogues. The final transformation of the FK4 to the FK5 will include the results of the determination of the equator and equinox of the FK5 carried out by Fricke (29.043.008). Status reports which include preliminary results for the equator and equinox were presented by Fricke (28.041.012; 28.043.001). According to the final result for the time-dependent correction to all right ascensions of the FK4, the transition from the FK4 to the FK5 equinox is achieved by the following operations CtFK4

+ 0~035

= Ct FK5 at 1950.0

Observations of relevance to the improvement of the equator have not indicated a significant correction to the FK4 equator. Hence, no change of the FK4 equator will be made in the FK5. The system of the FK5 is intended to be completed in 1983 and ready for introduction at 1984.0. The completion of the individual corrections to the positions and proper motions of the FK4 stars and the extension of the fundamental catalogue to fainter stars can be expected in 1985. Preparations have begun in Heidelberg for the participation in the compilation of the observing programme for the Astrometry Satellite HIPPARCOS of the European Space Agency and for the reduction of the satellite data. (W Fricke). (ii) At the Hamburg Observatory the programme of precise optical positions of

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radio sources has been continued. (25.031.567, 25.141.079, 25.141.080, 26.041.014). Source positions have been derived now for 30 quasars on the northern hemisphere. Part of the material has been obtained from a joint observation program with F Prochazka, Vienna Obs. A detailed investigation of optical - and radio positions for 3C273B has been finished (A & A 19811 The work on optical and radio reference system with the IAU working group has been continued. The project of a photographic reference star catalogue for the reduction of PZT-observations and the connection of neighbouring PZT-stations has been started with the zone astrograph as a contribution to MERIT. The catalogue will cover a closed belt of 50 width, centered at declo +52~5 with fourfold overlap. The area of the 4 PZT-stations Herstmonceux, Calgary, Potsdam, and Hamburg will be fully included. o 0 Reductions of the Cape astrometric Survey (CPC2), zone -42 to -52 , has been started in collaboration with C A Hurray and W Nicholson/RGO. (C de Vegt). (iii) At Hannover the work on an absolute stellar geographical fundamental system was continued (22.041.076, 25.041.043, 28.041.016). (K Pilowski). e) France At Bordeaux the automatic meridian circle has been used since 1980 for routine differential observations of NPZT stars. About 8000 positions have been obtained during 10 months which confirm the claimed mean errors of 0~10 in a and 0~13 in o. However, the automatic setting will be in service only by October 1981 and the determination of the division errors and the extension up to mV = 12.5 will not be carried out before 1982. The instrument is proposed to observe 15 000 faint HIPPARCOS stars and for specific high accuracy programmes. (25.032.036, 28.032.008). (Y Requieme). At Grasse the prototype photoelectric astrolabe has obtained a satisfactory precision of 5 to 5 ms on a transit time in the first vertical. (G Billaud). Results from the Paris astrolabe have been published and ana'lysed for Mars (25.097.036,26.097.026), A & A 96 (1981) 193 and for Saturn (22.041.005, 22.041.025). Previously discussed discrepancies about Mars have been explained (25.097.047, 25.041.015, 25.097.019). Synthesis paper about planetary astrolabe observations (27.041.034). Bibliography on astrolabe literature (21.002.061). Contribution to the celestial reference frame can possibly be made through observations of bright counterparts of radiosources, and an international cooperation for astrolabes has been started, see IAU ColI. No. 56, Varsovie, 1980. The first five systematic campaigns at the Paris astrolabe for beta Persei have appeared in A & A Supp. Ser. 44 (1981) 189. (S Debarbat). f)

Great Bri tain

All observations of FK4 stars made at Herstmonceux in 1957-1981 have, been reduced on the Herstmonceux system, and the results sent to 'the ARI at Heidelberg for inclusion in the FK5 catalogue. In addition, these observations have been transferred to the FK4 system, in order that they may be published on both systems. On the Cooke Transit Circle at Herstmonceux, regular observations of Sun, Moon, major and minor planets, and fundamental stars are continuing. The Electronic Circle Reading system has been delivered and installed. Some modifications have been made, and the equipment has shown that it can provide real-time circle readings of the required accuracy. The delivery of the apparatus gave a natural opportunity for termination of the programme~ of observations of zodical stars and NPZT stars. Work continues on clearing the arrears of publication of meridian catalogues, starting with the Greenwich Airy TC observations of 1942-1954. Morrison has succeeded Tucker as RGO Project Leader of the Carlsberg Automatic

POSITIONAL ASTRONOMY

Transit Circle. The main data-reduction computer for the Herstmonceux, transported to Brorfelde, and successfully dedicated to control of the telescope. Efforts are being estimated cost of the CATC building on La Palma to bring financial provision. (R H Tucker).

37

CATC was tested at linked to the computer made to reduce the it within the approved

g) Italy At Cagliari observations were started 1981 with the new Danjon astrolabe. A new photoelectric micrometer for the 12 cm transit instrument is planned for meridian observations of stars, planets and the Moon. Researches in the field of diurnal refraction deduced from observations of solar disk and anomalous refraction are pursued: A Poma, E Proverbio, and S Mancuso in W Fricke and G Teleki (eds), Sun and planetary system, Reidel Publ. C. (in press), and E Proverbio, S Uras in Mem. SAlt, Vol. 53 (in press). (E Proverbio). h) Japan At Mizusawa the International Latitude Observatory derived corrections to the declination of ILS latitude stars. It also continues to derive corrections to the positions of FK4 stars. C Sugawa and N Kikuchi showed the characteristics of astronomical refraction in the northern hemisphere (26.082.049), and S Takagi and Y Goto showed the formula applied to calculate the astronomical refraction at Mizusawa (26.082.050). At the Tokyo Astronomical Observatory, regular observations of the Moon, planets and the four bright minor planets referred to the FK4 system have been continued. The results of the observations of solar system bodies from 1974 to 1977 were published by Yasuda et al. (21.041.035). The meridian observations of 0 and B stars north of _30 0 have been completed by the end of 1979, and the observational catalogue of them is being compiled. Yasuda proposed a method with a new statistical approach to Brosche's model for catalogue comparison (21.041.011). M Miyamoto derived a method suitable for the computer analysis of division errors. A correction term to the refraction table is derived in an analytical expression by Yasuda and R Hukaya (26.082.043). Y Niimi determined the equinox and equator corrections to the FK4 system from meridian observations made during the period from 1935 to 1976. At Tokyo the compilation of 1179 Northern PZT Stars Catalogue has been completed by Yasuda and K Hurukawa. It is based on comparative meridian circle observations at Abbadia, Beograd, Bordeaux, Bucharest, Copenhagen, Herstmonceux, Moscow, Pulkovo,· San Fernando, and Tokyo Observatories. The average epochs of the catalogue in R.A. and Dec. are about 1974. The 95% of mean errors of catalogue positions is less than ±0~0060 (m.e. cos 8) and ±0~131 in R.A. and Dec. respectively. The determination of proper motions of NPZT stars is going on by Yasuda. An automatic photoelectric meridian circle is currently being manufactured by Carl Zeiss Oberkochen, and will be set up at Mitaka campus of the Tokyo Astronomical Observatory at the middle of 1982. This instrument can observe the Sun, the Moon, planets and stars brighter than 13.0 visual magnitude. It permits the preliminary observed minus computed position of a star to be produced on-line by PDP 11/34 and HITAC E-800 computers. (H Yasuda). i) Romania The Bucharest SRS catalogues were published in 1979. Observations of the Cagliari PZT stars were completed in 1979, and those of Prague PZT stars were started in 1980. The O-C differences for all FK4 stars of the Bucharest KSZ programme (1955-1962) will be computed and some of them have already been sent to ARI, Heidelberg. The NPZT declinations have been sent to Tokyo and R.A.s will soon follow. (E Marcus, I Rusu, M Tudor, E Toma).

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j) Spain The astrolabe at San Fernando has been used for observations of stars and the planets Saturn, Jupiter, Mars, and Vesta. Results were published in IAU Colloquium No. 48 (1979), A & A Supp. 41 (1980) and A & A, 96 (1981). Since 1980 fourteen radio sources from the Commission 24 list are being observed systematically. The NPZT programme of the meridian circle from 1973 to 1980 resulted in 4 observations for each of the 1717 stars and they have been sent to Tokyo. In addition 99 transits of planets were observed: Mars 22, Jupiter 31, Saturn 38, Uranus 8. Meridian observations of 38 radio sources were started in 1981. Since 1980 the Instituto y Observatorio de Marina (10M) is associated to the joint Anglo-Danish project for operation of the Carlsberg Automatic Transit Circle on the Island of La Palma. Astrograph observations of 20 minor planets of the Leningrad programme has resulted in 242 plates. (L Quijano, M Sanchez). k) USA Instrumental improvements on the three transit circles of USNO have been introduced. They have all been equipped with new digital motor drive systems on the micrometers. An image dissector micrometer is being tested on the 7-inch, while the 6-inch and 8-inch have visual micrometers. The former ATC with mirror optics has now been converted to a conventional 8-inch transit circle and it has obtained a new lens objective. The IBM 1800 system at the 6-inch is being replaced by an HP 1000. (B L Klock). 1) USSR At Pulkovo observations of 505 stars of the ?ulkovo latitude programmes have been obtained with t~e ~verev photographic vertical circle. Photoelectric observations of RA of about 500 circumpolar stars have been commenced with the modernized meridian circle MK-200 (0 = 200 mm, F = 2000 mm). Pilot observations of declinations of FK4 stars have begun with the Sukharev mirror meridian circle. The reduction of declination observations of SRS, BS, and DS stars (in the zone _47 0 to _90 0 ) with the meridian circle of the Cerro-Calan Observatory has been completed. Corrections to the declinations of FK4 stars have been derived from observations in the zone _40 0 to _90 0 and observations of series of reference stars in the zone +40 0 to _90 0 • Observations of 4000 stars of the latitude and photoelectric zenith tube programmes with the Ertel vertical circle and photographic observations of the catalogue of geodetic stars (northern sky) have been reduced. A catalogue of absolute RA of 1960 FK4 and FKSZ stars has been published. It was compiled on the basis of observations with the Pulkovo large transit instrument at the Cerro-Calan Observatory during 1969-1973. Three catalogues of absolute RA of stars from the Backlund-Hough, Kimura and Kopff lists compiled of observations at the Melbourne Observatory in 1928-1941 came out (Trudy of the Glavn. Astr. Obs., v. 84, 1981). Visual meridian observations of double stars (DS) and photographic observations of areas with distant radio sources have been commenced at several observatories of the USSR. Theoretical and practical studies concerning absolute determinations of quasar coordinates with the VLBI method are being made. Photographic observations of the bodies of the solar system are carried out. 1980.

From Golosseyevo, Kiev, three papers were published in Naukova Dumka, Kiev,

By A S Kharin, E M Nenakhova, P F Lazorenko: Modernization of the Wanschaff vertical circle and the results of observations of the Sun and the major planets in

POSITIONAL ASTRONOMY

39

1940-1947. By D P Duma, L I Kizjun, Yu I Safronov: Orientation of the FK4 frame using meridian observations of planets. By M S Zverev, A M Kurianova, D D Polozhentsev, Ya S Yatskiv: A compiled catalogue of fundamental faint stars with Dec. +90 0 to _20 0 , PFKSZ-2. A catalogue of declinations of 100 equatorial stars of the A A Mikhailov list was compiled (N F Minailo. Astrometry and Astrophysics, vyp. 43, 1981). At Kazan a differential catalogue of declinations of 2884 stars of latitude programmes has been compiled. An absolute catalogue of declo of 203 FK4 stars, a general catalogue of 2679 KSZ stars in the zone from _20 0 to _5 0 in declination on the basis of observations in Perth, Bucharest, Nikolayev, Tashkent, and Odessa and a compilation catalogue of declinations of KSZ stars in the zone _50 to + 90 0 on the basis of an improvement of the AGK3R with respect to accidental errors (Bucharest, Moscow, Kiev, and Kazan observations were used) have been finished. At Kharkov a catalogue of declinations of 1407 circumpolar faint stars has been compiled on the basis of the observations made in 1909-1914. Differential observations of RA of 650 double stars (DS) and 167 high luminosity stars (HLS) have been carried out. At Kiev University Observatory the compilation of a general catalogue of bright stars (BS) and observations of double star programmes (DS) and high luminosity star programmes (HLS) with the meridian circle have been continued. At Moscow the following catalogues have been compiled: A Catalogue of Declinations of 436 stars of the zenith zone from observations with the zenith-telescope. A catalogue of RA of 261 stars from observations with the PZT. A Moscow catalogue of 3696 stars of latitude programmes. The work on a compilation catalogue of radio source coordinates has been continued. Observations of cepheids, high luminosity stars and double stars have been continued with the meridian circle and of Venus and Mars with the wide-angle astrograph. At Nikolayev a catalogue of absolute RA of 531 stars have been compiled from observations on the West Spitzbergen. Other catalogues were completed: 431 stars from observations at Nikolayev; RA of 586 FKSZ stars; Decl. of 9560 zodiacal stars from observations at Nikolayev. Meridian observations and photographic observations of major planets, their satellites and minor planets have been continued. At Tashkent a catalogue of RA of 433 FK4 stars and a catalogue of RA of 376 stars in the declination zone from _20 0 to +90 0 is in press. Observations of RA of selected FK4 stars and day time observations of the bodies of the solar system are carried out with the meridian circle. At Leningrad theoretical and practical work has been done on the use of the VLBI method for the goals of positional astronomy. (K N Tavastsherna). m) Yugoslavia At the Belgrade vertical circle 308 bright circumpolar stars were observed 4 times in each of the upper and lower cUlminations by M Mijatov, Dj Bozhichkovich and G Teleki. At the Askania meridian circle the NPZT programme was completed and Sun, Mercury, Venus, and Mars are regularly observed. A programme of 3000 double stars has been started.

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Papers related to fundamental astrometry and astronomical refraction are (22.082.094, 22.032.020, 25.002.014, 25.041,049, 26.082.040, 27.032.039). PUbl. Obs. Astron. Sarajevo 1 (1981) contains papers b~ Teleki on refraction, by Bozhichkovich on meridian instrumentation, by Sadzakov, Saletic, and Dacic on NPZT observations and observations of Sun, Mercury, and Venus. Ed. Fan, Kazan, 1981, contains pape"rs (in Russian) by Teleki on fundamental astrometry and on refraction, and by Sadzakov, Saletic, and Dacic on NPZT observations. Publ. Astron. Obs. Belgrade 30 (1981) contains the catalogue of NPZT stars by Sadzakov, Saletic, and Dacic and a-paper on refraction by Teleki. (G Teleki, S Sad~akov). III. OTHER REPORTS a) Working Group on Astronomical Refraction (i) Chairman: G Teleki. Members: W J Altenhoff (Bonn), F K Brunner (Kensington), B Garfinkel (New Haven), J A Hughes (Washington), I G Kolchinskij (Kiev), A I Nefed'eva (Kazan), K Ramsayer (Stuttgart), J Saastamoinen (Ottawa), C Sugawa (Tokyo), E Tengstrom (Uppsala), and H Yasuda (Tokyo). (ii) The Group continues the work on the elaboration of the new international refraction tables. In the frame of this activity, J Saastamoinen (National Research Council of Canada) finished a study on the latitudinal distribution of meridian tilts in the atmosphere (1980), which gives a global atmospheric model. (iii) The Group and the Special Study Group 1.42 on Electromagnetic Wave Propagation and Refraction in the Atmosphere of International Association of Geodesy has decided to organize a workshop ~Three-dimensional Refraction~, as a Special Session of the Sixth European Regional Meeting in Astronomy. Organizers: F K Brunner, G Teleki, and E Tengstrom. The preliminary agenda contains 8 invited papers, 9 contributed papers and one round table discussion. (iv) G Teleki published (Bull. Obs. Astron. Belgrade, 131, 1981, pp. 3-8) a review on new tendencies of research in astronomical refraction. (G Teleki). b) Astrolabe Reports These have been given under the appropriate national headings of Chile, France, Italy, and Spain. c) Study Group on Horizontal Meridian Circles (i) Chairman: E H¢g. Members: R d'E Atkinson (Bloomington), J W Gietzen (RGO), G van Herk (Leiden), B L Klock (USNO), J Osorio (Oporto), G J Pinigin and G M Timashkova (Pulkovo), Xu Tong-qi (Shanghai), and Hu Ning-sheng (Nanjing). (ii) A communication by G I Pinigin was distributed to the members: ~Investigation of the Pulkovo horizontal meridian circle for observations of star declinations~ containing a study of refraction in horizontal tubes. (iii) On the glass meridian circle, GMC, four working papers have been distributed by E H¢g: Geometrical theory of a GMC; Aberrations of the GMC telescope; Study of air in a horizontal tube, Parts 1 and 2, The present design of the Danish GMC contains a short copper cylinder instead of the original solid glass cylinder which was found to be too difficult and expensive to manufacture and difficult to mount in any bearing. The copper tube will carry a plane 45 0 mirror at one end and a plane auxiliary mirror perpendicular to the optical axis at the other end. The high thermal conductivity of copper will ensure a constant angle between the two mirrors. A counterpoised mounting of a

POSITIONAL ASTRONOMY

41

dummy 45 0 mirror of 24 cm aperture is being tested on the copper tube with respect to mechanical properties. (iv) Studies of the GMC have started at the Astronomical Instruments Factory, Nanjing, in consultation with E H¢g. An overall theoretical study of the instrument has been written by Yao Zheng-qin (in Chinese) and experiments on refraction in a horizontal tube has been initiated by Hu Ning-sheng. (E H¢g). d) Theory of Nutation A mailing vote on the adoption of the 1980 IAU Theory of Nutation in replacement of the 1979 Theory was conducted in the Commission with the following result: 63 votes in favour, 1 against, 5 abstentions, and 45 members did not reply. e) SRS Project The most recent previous reports on the projects are: IAU Trans. Vol. XV B, 1973, p. 81,Comm. 8 report. IAU Trans. Vol. XVI A, Part 2, 1976, p. 9, Comm. 8 report. IAU ColI. No. 48, 1978, p. 489, on Pulkovo work on R.A. The observations of the different parts of the programme have been reduced and exchanged between Pulkovo and USNO except the Santiago-Pulkovo Dec. observations zone -47 0 to -90 0 and the Leoncito observations. The transmission of the last data awaits the completion of certain protocols. An SRS meeting of representatives from Pulkovo, Washington, and Heidelberg, and the President of the Commission will take place at Brorfelde in March 1982. It was proposed by K N Tavastsherna and at first arranged for October 1981, but it was postponed because the Pulkovo astronomers were not able to corne. (E H¢g). f) HIPPARCOS Satellite The ESA astrometry satellite was approved in March 1980 and is scheduled for launch in late 1986. It is expected to obtain positions, annual proper motions and parallaxes with an accuracy about 0~002 for about 100 000 stars, mostly brighter than B = 11. ESA has issued three Announcements of Opportunity (AO) calling for commitments to tasks in connection with the mission. 1. An AO for forming the Input Catalogue of presumably 100 000 stars. This catalogue shall contain all information needed for observation and reduction, such as positions to ±1", approximate magnitudes, parallaxes etc. 2. Another AO for Data Reduction. The reduction will be based on the photoelectric recordings, readings of gyroscopes etc. and shall give the final results in a catalogue. 3. An AO for proposals of observing programmes. It will perhaps be distributed to scientists outside the ESA member states (while 1. and 2. are limited to institutions in these countries). The proposals will be submitted to a selection committee which will select the stars to be observed, in case not all can be accommodated. Based on this selection the task 1. can be completed. Scientists and groups whose contributions are selected in 1. to 3. will have exclusive access to all HIPPARCOS data for a period of not more than 5 years from the date of launch. On the basis of the time expected to prepare the total catalogue, this should mean that these scientists will have exclusive access to that catalogue for a period of not less than one year. The activities associated with 1. to 3. will be financed by the institutions selected for the work and not by ESA. ESA has nominated a Project Scientist, MAC Perryman, and has appointed a HIPPARCOS Science Team (HST) led by the Project Scientist consisting of instrument'

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experts, astrometry experts, and astro-physicists. HST will provide ESA management with the appropriate scientific advice and assistance during the various phases of the mission. The industrial studies for the payload have started. It is noted that some doubt has previously been cast on the feasibility of the present optical system. Particularly on the feasibility of manufacturing the complex mirror with the deformed surface to the high accuracy of A/50. Other possibilities are being studied and it is expected that the revised optical system will perform to the accuracy predicted hitherto. Project TYCHO: In addition to the primary scientific result of extremely accurate astrometric data to be obtained for 100 000 stars by the main HIPPARCOS detection system ~0.002 arcsec) it appears that exploitation of the satellite's "star mappers"(originally designed to be used only for the attitude determination) can give further results of great scientific value. This can be achieved if the two' star mappers are provided with B and V colour filters, respectively, and if the complete photon record generated by the star mapper photomultipliers is transmitted to the ground for evaluation. The star mappers could observe at least 400 000 stars brighter than B = 11 with an accuracy at B = 10 of 0.03 arcsec for positions and 0.03 mag for the Band V magnitudes. Proper motions with an accuracy of 0.003 arcsec per year can then be derived for most of the 400 000 stars by comparison of the resulting positions with first epoch positions from the photographic catalogues AGK2, Cape, etc. The number of known bright variable stars (V < 10) of small amplitudes will be much increased compared to present knowledge, e.g. of most cepheid types and eclipsing variables. The resulting catalogue of positions, proper motions, magnitudes and colour indices would be about an order of magnitude more accurate than existing precise star catalogues and should carry the name TYCHO in honour of the creator of the first accurate star catalogue in Modern Time. This project proposed by E H¢g has marginal cost impacts on the present mission and was approved by ESA in December 1981. The photon records from the star mappers will contain valuable information for an additional 800 000 fainter stars. This information can be more easily and accurately extracted if positions and B and V magnitudes for all stars down to B=13 were available with an accuracy corresponding to one astrographic plate in each of the two colours. Thus, a collaboration between this part of the TYCHO project and ground based facilities is auggested. A Colloquium on the Scientific Aspects of the HIPPARCOS Mission is to be held in Strasbourg on 22-23 February 1982. (E H¢g). IV LATE REPORTS No late reports were received. E H¢g President of the Commission

,9. INSTRUMENTS AND TECHNIQUES (INSTRUMENTS ET TECHNIQUES) PRESIDENT: E.H. Richardson VICE-PRESIDENT: W. C. Livingston ORGANIZING COMMITTEE: T. Bolton, W. B. Burton, P. Connes, J. Davis, J. Heudier, I. M. Kopylov, A. Labeyrie, D. McMullan, A. B. Meinel, N. Mikhel'son, J. Ring, J.Rosch, N. Steshenko, G.A.H. Walker, M. F. Walker. I.

L. N.

MEETING AT THE 6 METRE TELESCOPE

The major activity organized by Commission 9 was IAU Colloquium 67, Instrumentation for Large Telescopes, held 8-10 Sept., 1981, on a portion of the observing floor of the 6 metre telescope of the Special Astrophysical Observatory, USSR. The cooling coils in the floor were turned off and a rug laid. The enormous BTA (Bolshoi Altazimuth Telescope) provided a spectacular back drop to the 88 participants. Between sessions, the particpants were shown every detail of the telescope by its Chief Designer, Dr. B. K. Ioannisiani, and SAO staff. Night observations continued: speckle interferometry. The Proceedings, edited by C. M. Humphries, and consisting of some 40 titles and three photographs at the BTA, will be published by Reidel as "Instrumentation for Astronomy with Large Optical Telescopes." There are four sections. 1) Telescopes (existing, e.g. 6 metre, MMT and CFHT; under construction, e.g. 4.2 metre Herschel and Iraqi 3.5 metre; and planned, e.g. 7.6 metre Texas and USSR 6 metre polar); 2) Spectrographs (including multi-object, wide field, and with and without slit); 3) Interferometers; and 4) Detectors. The smallest telescope described, 5 cm, is located at the most extreme site, the South Pole, and is used to measure solar oscillations by the Observatoire de Nice. Panoramic, 360 degree photographs were taken inside the BTA dome for the H. R. MacMillan Planetarium, Vancouver, Canada. (It gives the Planetarium audience the illusion of being inside the BTA dome with the 6 metre telescope which was turned horizontal with the mirror cover open for the photographs.) II.

TUCSON MEETINGS

On the occasion of the commissioning of the Multiple Mirror Telescope on Hopkins, a conference on "The MMT and the Future of Ground-Based Astronomy" held at the University of Arizona, Tucson, 9 May 1979. It is published as Smithsonian Astrophysical Observatory Special Report 385. The editor is T. Weeks.

Mt. was the C.

A larger meeting was held the next year: "Optical and Infrared Telescopes for the 1990s", 7-12 January 1980, a Kitt Peak National Observatory Conference, edited by Adelaide Hewitt. There are 72 titles and 202 participants. "SPIE - The International Society for Optical Engineering" sponsored a conference in Tucson in January 1979: "Instrumentation in Astronomy III", Volume 172. Two conferences are planned for Tucson in 1982, both sponsored by SPIE and The American Astronomical Society: "Instrumentation in Astronomy - IV", 8-10 March, and "Advanced Technology Optical Telescopes" 11-13 March.

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III.

OTHER MEETINGS

An ESO Conference was held at Garching, 24-27 March 1981, on the "Scientific Importance of High Angular Resolution at Infrared and Optical Wavelengths," edited by M.H. Ulrich and K. Kjar. There were 119 participants and 37 papers. Commission 9 joined with the International Commission for Optics for the Congress and Twelfth Assembly, "ICO-12", held in Graz, Austria, 31 August to 5 September, 1981. Proceedings will be published in Optica Acta. A progress report on the NASA Space Telescope is included. Several other meetings of the SPIE were related to astronomical instruments. The titles, volume number, and place are as follows: IR Image Sensor Technology, Volume 225 (Washington, D.C. 1980); Periodic Structures, Gratings, Moire Patterns and Diffraction Phonomena, Volume 240 (San Diego 1980); Cryogenically Cooled Sensor Technology, Volume 245 (San Diego 1980); Applications of Digital Image Processing to Astronomy, Volume 264 (Pasadena 1980); IR Astronomy Scientific/Military Thrusts and Instrumentation, Volume 280 (Washington, D.C. 1981); Solid State Imagers for Astronomy, Volume 290 (Harvard 1981); Mosaic Focal Plane Methodologies II, Volume 331 (San Diego 1981). IV.

PROGRESS OF TELESCOPE PROJECTS

At the SAO, a new 6 metre mirror of low (but not zero) expansion material has been substituted for the original (which is now outside in storage and might be used for an inexpensive, stationary polar telescope designed to study very faint objects in a 36 arcmin field near the pole). The telescope can now concentrate up to 90% of the light in 0.82±0.05 arcsec. For improvement of the thermal environment of the mirror, a local fan system has been installed. A 6 metre mirror blank of "Sitall" rejected as not good enough for polishing.

zero expansion material was

cast

but

The Multiple Mirror Telescope on Mt. Hopkins, Arizona, consists of six 1.8 metre axially symmetric mirrors on a single mount. The MMT and its instruments are described in the publications mentioned above. Latest reports are that the seeing has proven to be outstandingly good on Mt. Hopkins and in the MMT building. The laser stabilization system was not successful but the mechanical stability of the mounting is very good and permits tracking on the superimposed images for several minutes without correction. A new system will be installed using computer controlled off-set guiding from each mirror to automatically keep the images superimposed and will have the added advantage of removing seeing induced image motion from the individual mirrors resulting in better light concentration than could be achieved from a single telescope of equivalent aperture: 4.4 metres. The CFH (Canada-France-Hawaii) 3.6 metre telescope is now in regular operation but all of the original instrumentation is not yet completed. Standard equipment at the Prime Focus is a modified Wynne corrector with the option of replacing the third element by a special wedged element with a coarse grating deposited thereon, called a "grens". This combination produces slitless spectra over a one degree field with a magnitude limit in a 1.5 hour exposure of 21 at 1000 A/mm and 22 at 2000 A/mm on IIa-J emulsion. The first visiting observer at the CFHT was G. Lemaitre of Marseille Observatory (March 1980) who brought with him an aspherized grating spectrograph which he had built using his elastic deformation technique. A plane aspherized grating replaces the more common grating + twice-through Schmidt plate combination. This 90 A/mm spectrograph uses a photographic plate as detector, covers a wide region (3000 - 5000A) and reached 18th magnitude in 2 hrs. In 1981,

INSTRUMENTS AND TECHNIQUES

45

a concave holographic reflection grating spectrograph was brought by the University of British Columbia and used at the prime focus. It consisted of only the grating, a flat diagonal mirror, and two windows for the cold box and the microchannel intensified CCD detector. The spectrograph covers the region from 4000 to 8000A at 160 A/mm, 12% of which is intercepted by the CCD. The 22nd magnitude was reached in 30 minutes at 12A resolution in the 3900-4400A region with a signal-to-noise ratio of 5. The dome design of the CFHT has been exceptionally successful in preserving the seeing which has been one arcsec or less about one half of the time with 0.6 arcsec a common occurrence. The small-mirror, turreted, high reflection coude mirror train has succeeded in reducing both light loss and seeing degradation. The first coude spectrograph, with dispersions as high as 2.7 A/mm, is in regular operation but not yet in its final form. A Reticon is the most popular detector and changes in velocity of 25 metres/sec can be detected using a Hydrogen Flouride absorption cell for the wavelength comparison. A Michelson interferometer, designed for the Cass focus, is in temporary use at the coude focus. The F/8 Cassegrain mirror was finished in 1981 and after it is installed and tested the 1.8 metre test sphere will be used as a camera in the coude spectrograph. A horizontal solar telescope was constructed at Pulkovo Observatory and mounted in Cuba. The diameter of the coelostat is 300 mm and the primary mirror is 290 mm, 9700 mm focal length. The spectral range is 3900-6600A. The nearly complete 3.5 metre telescope of the Max Plank Institute will be installed in Spain in 1982. A similar 3.5 metre telescope, has been ordered by the Iraqi National Observatory. In Argentina a 2.2 metre telescope is being erected at El Leoncito Observatory. This telescope is a twin of the KPNO 84 inch, but the coude system will be changed to one using small, high reflectance mirrors. The Burrell Schmidt 60 cm F/3.5 telescope was moved from Cleveland to Kitt Peak, and a new 10 degree dense flint objective prism added to complement the existing 4 and 2 degree prisms. . In China, 2.16 and 1.56 metre telescopes are under construction. Zero-expansion glass-ceramic blanks up to 3.5 metre diameter can be produced, called "VO-2." The 4.2 metre, altaziumth, under construction. It will be del Roque de los Muchachos, at Among the proposed instruments metre Isaac Newton Telescope is

William Herschel Telescope has been funded and is installed on La Palma as part of the Observatorio an altitude of 2300 metres in the Canary islands. is a novel collimatorless spectrograph. The 2.5 already being moved to La Palma.

IV.

FUTURE TELESCOPES

A 25 metre telescope with a spherical, mosaic primary mirror (and a 6 metre monolithic secondary mirror) has been proposed in the USSR. In this connection, a 1.2 metre telescope having a spherical primary composed of 0.4 metre segments has been tested at the Crimean Astrophysical Observatory (Proceedings of MMT Conference). Two-mirror designs for spherical primaries have been studied (B. A. Gurnasheva et al., Izv Krimskoy Astrofiz Observ 1981, 63.) At Odessa Astronomical Observatory, a three mirror system with a spherical primary was designed and tested. A

consortium

composed

of

the

Kitt

Peak

National

Observatory

and

the

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Universities of Arizona, California, and Texas has been funded for research to develop the technology for a 15 metre telescope. It is planned to decide between two approaches in 1983: the MMT (multiple mirror telescope) and the SMT (segmented mirror telescope). For the MMT honeycomb Pyrex mirror blanks are being cast at the U of A and will be tested on the existing MMT. For the SMT, 2 metre off-axis paraboloidal segments, 7.5 cm thick, are being figured at KPNO by the bend-and-polish method, and segment alignment controls are being developed at the U of C. U of Texas has been working on the design of a monolithic 7.6 metre telescope. At the DAO, a light weight 3 metre telescope has been designed and is intended to operate either as a single telescope or in an array. Some of the passive mirror support units (which use flex pivots) have been made and are being tested using a small (30 cm) mirror having the same thickness and radius of curvature as the F/2, 3 metre, 24-1 meniscus primary mirror. VI.

NEW INSTRUMENTATION

Several new instruments are now in operation at the 6 metre BTA. At the Prime Focus: a digital speckle interferometer (ref. Yu.Yu. Balega, A. N. Kasperovich, Yu. A. Popov, N. N. Somov, A. F. Fomenko, Avtometriya (USSR) No.3, 1980); a digital dissector photomultiplier for spectra and photometry with a photometric accuracy of up to 0.1% and a time resolution of 0.1 second; a slit less spectrograph with a transmission grating covering a field of 13 arcmin at dispersions of 1400 to 400 A/mm; a fast image tube spectrograph. At the secondary focus, the thermal stability in the fork tyne (where the spectrographs are located) has been improved, and the third Schmidt camera, Fll, is now in use. At Steward Observatory a multi-object slit spectrograph has been built using fibres to align a field of images along the slit. The positioning of the fibres is being automated. Observatoire de Marseille and Laboratoire d'Astronomie Spatiale du CNRS produced an Fll focal reducer which has been used with the 6-metre BTA for observation of extended sources. Also, a "high space resolution integral field spectrograph" uses an array of lenses and fibre optics to give individual spectra of alII" xl" elements in the focal plane of large telescopes. A coronograph, similar to that of the space telescope, has been adapted to the Mont Chiran 1 metre and ESO 3.6 metre telescopes for the detection of faint features in stellar and planetary observations. At ESO, a special reflectometer was constructed to measure the actual reflectivity and polarization of multilayer coatings (which can be different from that on the test pieces.) An echelle spectrograph was added to the coude of the 3.6 metre telescope in Chile, and a 3-element wide field corrector installed at the prime focus. At KPNO, a cryogenic, Fll, CCD camera utilizing a grism element was added to the 4 metre spectrograph. A zero-deviating predisperser for optical bandwidth selection is now available, replacing filters, for the 1 metre Fourier Transform Spectrometer. At CTIO, image slicers were added to the coude spectrograph of the 1.5 metre telescope. An infrared photometer was completed at Tartu Observatory in 1980. It measures in the four bands of the Arizona photometry and reaches stars as faint as 8.5 m at 2.2 ).lm with the 1.5 metre telescope. An infrared photometer for the 1.2-2.5 ).lm region was built for use on the Bjurakan 2.6 metre telescope. For the 10 ).lm region a heterodyne infrared detector of the University of Toronto will be used on the NASA 3 metre telescope in Hawaii.

INSTRUMENTS AND TECHNIQUES

VII.

47

SITE TESTING

An extraordinarily comprehensive site testing project is now under way in Saudi Arabia headed by E. Brosterhus, seconded from the Dominion Astrophysical Observatory, Canada. Four mountain si tes are being tes ted simul taneously using automated seeing monitors run by four observers at each site. VIII. PHOTO-ELECTRONIC IMAGE DEVICES Report from the Working Group, W. Livingston, Chairman Following tradition, reports have been solicited from Commission 9 members in an attempt to survey progress since the 1979 Montreal meeting. The pertinent efforts of almost a hundred workers thus came to our attention. Limitations in space force us to restrict this .summary to information on devices and techniques that have been employed on telescopes post-Montreal. Furthermore, in the case of Charge Coupled Devices (CCDs) for example, only representative programs are described. For more detail than can be given here, and for the intriguing story of devices intended for space telescopes yet to be deployed, consult the following proceedings and reviews: a) Electronography At the Paris Observatory M. Duchesne and colleagues, benefiting from new laboratory facilities, now produce a variety of photocathodes (Sl, S11, and S20) which are extremely uniform and efficient. G. Wlerick and B. Servan have used the 81-mm Lallemand Electronic Camera (EC) on the Haute Provence 1.9 m for direct observations of active extragalactic objects. Another E.C. is currently in operation on the 3.6-m CFHT. A detection of V = 25.2 m with a 4 0 certainty was achieved in an exposure of one hour by a group from Meudon. Other recent EC activity includes that of M. Walker (Lick) and J. Andersen (Copenhagen), who have used the 80-mm McMullen camera on the 1.5-m at La Silla for B,V photometry of the Magellanic Clouds. In Flagstaff H. Ables and A. Hewitt [3J devised a new flat-fielding method for aKron EC-improving their UBV standards program (11-22 m). UV spectra in the 950-1800A region were obtained in 1980 by G. Carruthers, and collaborators, with his opaque CsI photocathode EC, transported by Aerobee rockets. He is currently testing a variety of novel UV EC for possible future space missions. b) Image Intensifiers At the Special Astrophysical Observatory (USSR) A. Afanasjev and A. Pimonov have installed a UM-92 3-stage magnetic reflector focus intensifier on an f/1.5 spectrograph of the 6-m reflector. We note that at this time image intensifiers by numerous manufacturers, mainly products of the decade past, are the contemporary workhorses of astronomy. No new development work is reported. Presumably this is in deference to the promise of solid-state arrays, even though the latter have yet to be widely proven astronomically. c) Solid State Arrays - CCD (Charge Coupled Device) In the Fall of 1981 there is a dearth of commercially available CCDsj only RCA and Fairchild offer reasonable delivery times. A few experimental CCDs have been provided to astronomers including the Fairchild 720 x 244 pixels (proposed in Montreal), the GEC-UK 576 x 385, and the BNR 100 x 100. Other CCDs of very

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restricted availability are the Texas Instrument 800 x 800 and an array made in the Peoples Republic of China at size 64 x 64. All the above arrays have been evaluated under actual astronomical conditions but since only the RCA chip is readily accessible, it is receiving the most attention. In fact some 23 different Institutes and Observatories report on its application. The RCA S12 x 320 is a buried channel thinned device. Its advantages include (1) availability (2) an RQE (Responsive Quantum Efficiency) > 70% from 4000-8000A and (3) relative insensitivity to cosmic rays. Disadvantages are (l) fringing at a level of S to 20% modulation (2) a low-light level charge-transfer failure and (3) a readout noise of SO-80e. Fringing, or the presence of wavelength dependent, pixel dependent, channel spectra is a particular problem. Depending on the application fringing may set the performance limit. In general all CCD's suffer at some precision level from fringing, and our ability to adequately flat-field the device worsens as the detector excels photometrically, as discussed recently by W. Baum [4]. Astronomically the productive use of the RCA chip has been demonstrated by B. Oke (Palomar Obs) [4] on the Casso spectrograph of the S.lm telescope and by J. Geary and D. Latham on the 4.S-m MMT [4]. The TI (Texas Instrument) 800 x 800 has been operated in Kitt Peak's cryogenic camera. Mounted on the 4-m spectrograph with an f/l Schmidt, a resolution of lSA is achieved from 4800-11000A in S steps with interchangeable grisms. In place of a single slit a custom aperture plate permits the simultaneous observation of up to 20 objects, each accompanied by adjacent sky (H. Butcher). Some loss of resolution is found because the thinned TI chip is not flat but rather "crinkled" i.os mm. d) Solid State Arrays - CID (Charge Injection Device) Both the GE-USA limit for high light Peak), T. Duval Jr., which spans about 40 I-minute observation.

100 x 100 and 244 x 248 CID have been pushed to a precl.sl.on level applications in solar spectroscopy by J. Harvey, (Kitt (NASA), and E. Rhodes, (Univ. S. California). A solar line pixels can be centroided to about 1/1000 of a pixel for a This corresponds to a velocity uncertainty of 2S em s-l.

e) Solid State Arrays - "Reticon" Type (Array of self scanned diodes.) Self-scanned diode arrays are commonly found on coude spectrographs these days - 11 observatories indicating their current use. The Reticon has a wide band of response from atmospheric cut off (29S0A) to about 10000A. The red RQE is temperature dependent though not markedly so. S. Vogt (Lick) finds the device response down only SO% at 1.0 micron when cooled to -130 0 C. He presents in ref. 4 a nice set of examples of 1 x 1872 Reticon spectra ranging from Call Hand K (S/N a 100 in 34 m exposure, nA = .36A, V = 4.7 m, S6 Peg) to Fe H at 100S7A (S/N 114 in 20 m, nA = 1.4A, V = 10.3 m, EV Lac). At the University of Texas R. Tull continues to implement the use of Reticons with S systems deployed on coude and Cass spectrographs. The new Mark-III K-coronameter on Mauna Loa utilizes a 1 x S12 Reticon allowing coronal transients to be seen for the first time from the ground (R. Fisher, High Altitude Obs).

INSTRUMENTS AND TECHNIQUES

49

f) Solid State Arrays - Infrared Array devices for wavelengths longward of 1 micron have been under development for more than a decade but only now are appearing on telescopes. F. Si bbille (Lyon and Meudon), with the engineering assistance of F. Gillette (Kitt Peak), have used a 32 x 32 InSb CID GE-USA on the KPNO 2.1 m for the speckle observation of IR source diameters. The array suffers some lag (Le., suffers from residual image) and is probably system noise limited even at full well (i.e., when saturated). But it is sensitive at 2-3 microns and suitable for speckle. Another forerunner of arrays to come is a 32 x 32 Bi-doped Si CID made by Aero-Jet. J. Arens (Goddard) and W. Hoffmann (Steward) have successfully used the array in the 12 micron window for mapping the Kleinmann-Low Region in Orion. g) Image Photon Counting Systems - IPCS Ten observatories report the more-or-Iess routine operation of an IPCS. The IPCS is customarily a hybrid device which can be made up of quite varied components. The Laboratoire d'Astronomie Spatiale and the Obs. Marseille have constructed a 512 x 512 IPCS consisting of an MCP (micro channel plate -- not male chauvinist pig) + SIT (silicon intensified target) manufactured by Thomson (UK), G. Courtes, B. Fort, J. Boulesteix, et al., have regularly used this instrument on both the 1.9 m (Haute Provence) and the 6.0 m (Zelenchukskaya), mostly for direct narrow band work. At the Special Astrophysical Obs (Zelenchukskaya), I. Balega et ale have in operation a 2 x 500 IPCS consisting of the "UM-92" plus a supersilicon (Vidicontype) tube. It has seen service on the f/1.5 spectrograph of the 6 m telescope. Centroiding is employed [5J. Other new and interesting systems include the Mount Stromlo-Siding Spring 760 x 480 IPCS (a 25 mm MCP + Fairchild CCD). Centroiding effectively doubles the detector resolution, T. Stapinski, et ale After many years of effort by J .G. Timothy the Multianode Array (MAMA) is showing astronomical results. Collaborating with J. Linsky and others the MAMA has produced excellent high resolution spectra in a search for stellar magnetic fields. The work continues on the 1.6 m McMath. A system which allows the speckle interferometry of objects as faint as V = 16 m has been installed on the Steward 2.3 m (E. Hage et al.). A 4-stage Varo intensifier coupled to a ''Plumbicon'' television camera tube produce near saturated video single photoelectron events [3J. h) Electronography vs CCD vs IPCS, etc. The variety of image detectors being pursued remains large and in some ways bewildering. But each device has its own strength and suitability for a class of observational problems. For example one might think for faint object spectroscopy a TI 800 x 800 CCD (Gunn and Westphal) with its RQE > 50% and noise < 10e might be superior to an IPCS (e.g. Boksenberg; 4-stage EMI + Plumbicon) with RQE ~ 10%. If the object sought is an emission line QSO it requires only a few detected photoelectrons to define each line, and then the wavelengths of many lines may be averaged to obtain a reliable red-shift. In this instance the IPCS wins easily over the CCD. However, if it is a matter of absorption line detection the CCD may be the choice. We note, too, that the limiting magnitude of 26.0 reached via the

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CCD (Gunn and Westphal [41 is similar to 25.2 attained by electronography (Picat, et al. [51. Seeing is no doubt a factor here. i) Software Development Practically every instrument mentioned in this report is computer intensive in practice. That is, each device imposes, pixel by pixel, a photometric signature of dark current, wavelength-dependent gain and possibly linearity. To the extent that these variables are constant with time the incident astronomical image can be recovered through proper flat fielding while data taking, and then rectifying the errors by computer manipulation. Evidently the better the device photometrically, the more subtle the corrections become and, ironically, the more difficult the task. C.R. Lynds has remarked that for reasons unknown, perhaps unknowable, an early version of the CCD (the Fairchild 190 x 244) had superior photomet ric properties not found in recen t devices. It was linear to well below the threshold noise level of 'V 15e. The bias produced by single electrons can be noticed at low spatial frequencies. See also the comments of D. Monet (Mt. Wilson Obs) [41. C.R. Lynds and associates at Kitt Peak are developing sophisticated algorithms to rectify Space Telescope Wide-Field Camera CCD data. J .A. Tyson (Bell Labs), C. MacKay (Cambridge), W. Baum (Lowell), and many others report extensive work peculiar to their astronomical objects and receptors. A video camera/CCD standards consortium has been established (C. Christian, CFHT) • All of the above efforts should benefit from cooperation, preferably on an international scale. REFERENCES Ref. 1.

Ford Jr., W.K.: 17, pp. 189-212.

Ref. 2.

"Cryogenically Cooled Sensor Technology", Proceedings of Conference in San Diego, 29-30 July 1980, Proc Soc Photo-Opt Instr Eng (SPIE) 245, R.J. Huppi, ed

Ref. 3.

"Applications of Digital Image Processing to Astronomy", Pasadena, 20-22 August 1980 SPIE 264, D. Elliot, ed

Ref. 4.

"Solid-State Imagers for Astronomy, Cambridge, Mass., 10-11 June, 1981, SPIE 290, J .C. Geary and D.W. Latham, eds (SPIE publications can be obtained from SPIE, P.O. Box 10, Bellingham, Washington 98227, U.S.A.)

Ref. 5.

"IAU Colloquium No. 67, Instrumentation Zelenchukskaya, 8-10 September, 1981.

1979,

"Digital Imaging Techniques"

for

in Ann

Large

Rev A A

Telescopes",

IX. HIGH ANGULAR RESOLUTION INTERFEROMETRY Report by the Chairman of the Working Group, Dr. J. Davis a) Introduction The following report has been based mainly on replies received to a circular letter sent to all groups and workers known to be active in the field of high angular resolution interferometry.

INSTRUMENTS AND TECHNIQUES

51

The proceedings of LA.U. Colloquium No. 50 "High Angular Resolution Stellar Interferometry", held at the University of Maryland in August, 1978 have been published (1). Sessions on interferometry have been included in several meetings recently indicating a growing awareness of the potential of this field now that modern technology promises the ability to overcome the problems that have restricted its progress. An example was the discussion of interferometric techniques and their application to binary star studies in sessions organized by H. McAlister at I.A.U. Colloquium No. 62 (Flagstaff, May 1981). b) Speckle Interferometry and Image Reconstruction i) Speckle Interferometry. A decade has now passed since Labeyrie (2) invented speckle interferometry, a technique that uses short-exposure images to achieve diffraction-limited angular resolution from Earth-based telescopes. There are currently at least eight groups who have built or are building instruments for visible-light speckle interferometry. The following list gives their locations and names of representatives of each group: CERGA, France (Labeyrie), ErlangenNumberg University, Germany (Weigelt), Georgia State University, U.S .A. (McAlister), Harvard University, U. S .A. (Nisenson/Stachnik), Imperial College, U.K. (Morgan), Kitt Peak National Observatory, U.S.A., Steward Observatory, U.S.A. (Hege/Strittmatter), University College, U.K. (Boksenberg). The most significant instrumental development has been the use of photon counting methods of image recording and real time analysis. For several years, theoretical studies predicting limiting magnitudes in the range mv = 18-20 have been viewed sceptically by many observers. Recently, Arnold et al. (3) and Hege et al. (4) have reported measurements on Pluto and QSO PG 1115+08 respectively at mv 16; the latter observations are of particular topical interest, since gravitational lens theory predicts another, as yet unresolved, component of this "multiple" quasar. Morgan et al. (Imperial College) have constructed a fast, vector autocorrelator for on-line analysis of photon-counting data which has several display modes to aid interpretation as data are being taken. The Harvard group currently uses videotape as an intermediate storage medium and is developing a novel photon event counting detector system that records the space and time co-ordinates of detected photons. Aime et al. (5) have made systematic measurements of the transfer function of speckle interferometry. ii) Image Reconstruction. Progress on image reconstruction has been concentrated in three areas; extending the technique of speckle interferometry, new interferometric techniques and adaptive optics. Fienup (6) has shown, using computer simulations, that the modulus of the object Fourier transform alone can sometimes be sufficient to reconstruct a map of the object; the plausibility of this result is discussed by Bruck and Sodin (7), but the uniqueness is disputed by Huiser and van Toom (8). For certain special cases, for example when there is a reference star in the field, speckle holography (9) can yield a map of the object. Image reconstruction based on only the modulus of the object's transform has the advantage that it directly utilizes the output of Labeyrie's speckle interferometry. Slightly less convenient, but still not requiring any optical processing or special interferometers, are methods in which the speckle data (shortexposure images) are processed in an alternative way; two examples are the methods of Lynds et al. and Knox and Thompson. Bates and Cady (10) have extended the method of Lynds et al., coining the description "shift and add"; this method is based on the assumption that the brightest speckles are noisy images of the object. Nisenson and Stachnik (11) have implemented their extensions of the KnoxThompson algorithm. Another approach to using interferometric data is to optically preprocess the image prior to detection - heterodyning is one possible example. Walker (12) has

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drawn attention to a method first proposed by Mehta. Roddier et al. (13) and Roddier and Roddier (14,15) have described how rotation shearing interferometry can yield diffraction-limited images of stellar objects. Adaptive optical techniques can also be used for diffraction-limited imaging, although they are fundamentally limited to relatively bright objects. Hardy (16) describes the performance of a 21-zone device at Sacramento Peak Observatory on both compact and extended sources. At the moment, the cost of such systems precludes their use in astronomy. c) Infrared Interferometry An improved version of the one-dimensional speckle technique has been developed by D.W. McCarthy and F.J. Low at the University of Arizona for spatial interferometry in the infrared. The image of a star or galaxy, produced by a large telescope, is scanned rapidly across a single narrow detector. The resulting signal is analysed to produce accurate and repeatable one-dimensional visibility functions. Data from 2 to 12 ].lm have been obtained at the Steward Observatory 2.3 m telescope for a variety of stars with circumstellar envelopes including a number of protostellar objects such as Mon R2 and W3. In collaboration with F. Gillett of KPNO and S. Kleinman of MIT the 4 m telescope has been used to partially resolve the nucleus of the bright Seyfert galaxy NGC 1068. These data, at 2.2 ].l m and 3.4 ].lm, show the existence of a bright nuclear core of diameter less than 0.1 arcsec.

A 10 ~m heterodyne interferometer has been employed for astrometric tests by E. Sutton, S. Subramanian and C. Townes, using McMath telescopes at Kitt Peak. Wi th a baseline of 5.5 m, a night to night precision of 0.08 arc sec rms was obtained for the angular separation of stars as large as 50 degrees. These small variations are primarily due to the mechanical instability of the telescopes and not to atmospheric causes. d) Visual Long Baseline and Multi-Aperture Interferometry There are three groups actively working at developing long baseline interferometers for operation in the visual part of the spectrum. These groups are based at the University of Sydney (Hanbury-Brown and Davis), at the University of Maryland (Currie) and at CERGA, France (Labeyrie). The Sydney group are developing an 11 m baseline prototype of Michelson's stellar interferometer (17) in which the aperture size is restricted to select essentially flat portions of the wavefront, wavefront tilts are removed by active optical components and rapid sampling of the interference removes the effects of randomly varying phases. In June 1981 the siteworks and housing for the prototype were nearing completion and installation of the component parts of the interferometer was planned to commence towards the end of 1981. The prototype is the first stage in the planned development of a major instrument with baselines up to 'V 1 km. The Maryland group, led by Currie, are also developing a prototype instrument, which has been described by Liewer (1), based on their amplitude interferometer (18). The prototype has a baseline of 'V 3 m oriented parallel to the Earth's rotation axis and is being installed at the optical research facility of the Goddard Space Flight Center. This instrument is designed to work at baselines up to 50 m when installed at a permanent observing sight. Currie has also continued the development of the multi-aperture amplitude interferometer which he ultimately intends incorporating in the long baseline interferometer. At CERGA work has continued with the prototype long baseline interferometer

INSTRUMENTS AND TECHNIQUES

53

(19) which employs 26 cm aperture telescopes and baselines in the range 5 to 35 m. Efforts to improve data acquisition and analysis have been reported by Koechlin and these are anticipated to lead to improvements in accuracy of angular diameter measurements to the order of 5%. Labeyrie has continued his programme to develop a large aperture synthesis array (20) and the first 1.5 m aperture telescope with novel concrete housing has been installed and has undergone extensive tests on its unusual drive system. It is planned to assemble a second telescope and operate the pair as a long baseline interferometer with baselines up to 60 m in the first instance. Shao and Staelin of MIT have successfully tested a prototype 1.5 m baseline phase tracking stellar interferometer. Continuous fringe phase and amplitude measurements have been made using 1.27 cm apertures under 2 arcsec seeing conditions for Polaris (21). These preliminary measurements show that B.7 to 10 magnitude stars should be observable with two 12.5 cm aperture telescopes. A 3 m baseline phase tracking stellar interferometer for astrometry is currently under development. This instrument will have 5 cm apertures and a field of 10. e) Interferometry from Space Several workers have carried out preliminary investigations of possible high angular resolution interferometers for operation above the atmosphere. These include Currie (Maryland), Hammerschlag (Utrecht), Kibblewhite (Cambridge, UK), Labeyrie (CERGA) and Stachnik et al. (Cambridge, USA) As an example of the results of this type of study, Stachnik reports that he and his colleagues have found that the technology for a 10 km baseline system consisting of two one-metre telescopes and a central station for fringe measurement, while different from that required for a monolithic device with a baseline of tens of metres, is not notably more complex. Whether monolithic or detached, a long baseline space interferometer would be an active optical system requiring precision location and positioning of the optical elements. Combining existing spacecraft precision location, pointing and ranging technology with low thrust-high efficiency electric propulsion systems, a judicious choice of orbits and an appropriate fringe search algorithm makes baselines of many kilometres quite plausible. Specific conclusions of this study are that (i) 10- 5 arcsecond resolution is possible; (ii) for circular 1000 km equatorial orbits differing slightly in inclination, the central station remains within 5 mm of optical pathlength equality during the first orbit, with no expenditure of fuel, while the 10 km baseline is repeatedly scanned; (iii) existing ranging, pointing and tracking technology are adequate, even without use of a ranging interferometer, to predict the location of the stellar fringes to within 1 cm over the 10 km baseline; (iv) a combination of an electric propulsion system consisting of four gimballed thrusters and an on-board optical delay line would permit fringe acquisition within the 1 cm region for sources as faint as my = 15 to lB. f) Scientific Importance of High Angular Resolution at Infrared and Optical Wavelengths A conference entirely dedicated to this subject was held by ESO at Garching March 24-27, 1981, at which it was very strongly emphasized that optical resolution equivalent to that obtained by the VLBA at radio wavelengths will be essential for future progress. With a baseline of the order of 300 metres objects as faint as magnitude 20 could be observed in an hour with a 300A bandpass with a resolution of 0.3 milliarc seconds at 5000A. With instruments of this type the broad line region in Seyfert Galaxies could be resolved (M. H. Ulrich) as well as highly compact structures in galactic nuclei and quasars (M.J. Rees). A proposal for realizing such an instrument at minimum cost was given by G. Odgers, namely to combine the 3.B metre UKIRT and the 3.6 CFHT on Mauna Kea giving an interferometer

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of 350 metre baseline. The envelopes of protostars could be observed with this resolution (N.W. Yorke) as well as stellar winds and chromospheres (F. Schatzman) and star formation itself (P.A. Strittmatter). An interferometer for space was proposed by A. Labeyrie which would have a baseline of 200 metres, resolution of 0.1 milliarcsec, limiting magnitude of 26, with 1 metre mirrors. A very long baseline (10 km) intensity interferometer was proposed by D. Dravins. Such an instrument could observe very bright objects with an angular resolution of approximately 10- 5 arcseconds. It would be possible to detect fine structure of stellar surfaces. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

"High Angular Resolution Stellar Interferometry" (r.A.U. Colloquium No. 50),ed. J. Davis and W.J. Tango (Chatterton Astronomy Department, School of Physics, University of Sydney), 1979. Labeyrie, A.: 1970, A & A 6,85. Arnold, S.J., Boksenberg, A., and Sargent, W.L.W.: 1979, Ap J 234, L159. Hege, E.K. et ale: 1981, ApJ 248, LI. Aime, C. et ale: 1979, Optica Acta 26,575. Fienup, J.R.: 1978, Opt Let 3, 27. Bruck, Yu M. and Sodin, L.G.: 1979, Opt Commun 30, 304. Huiser, A.M.J., and van Toorn, P.: 1980, Opt Lett 5, 499. Weigelt, G.: 1979, Optica Acta 26, 1351. Bates, R.H.T., and Cady, F.M.: 1980, Opt Commun 32, 365. Nisenson, P. et ale: 1980, Proc SPIE 243, 88. Walker, J .G.: 1981, Optica Acta 28, 1017. Roddier, C. et al.: 1981, Conf Proc ESO, Munich. Roddier, C., and Roddier, F.: 1981, Conf Proc ICO, Graz. Roddier, F., and Roddier, C.: 1981, Conf Proc IAU ColI No. 67, Zelenchuk, USSR. Hardy, J.W.: 1981, Proc Conf ESO, Munich. Davis, J.: 1979, New Zealand J Sci 22, 451. Currie, D.G., Knapp, S.L., and Liewer, K.M.: 1974, Ap J 187, 131. Labeyrie, A.: 1975, Ap J 196, L71. Labeyrie, A.: 1978, Ann Rev A A 16, 77. Shao, M., and Staelin, D.H.: 1980, Appl Opt 19, 1519. Ulrich, M.H. 1981 Conf Proc ESO Munich Rees, M.J. 1981 Conf Proc ESO Munich Odgers, G.J. et ale 1981 Conf Proc ESO Munich Labeyrie, A. 198Y-Conf Proc ESO Munich Dravins, D. 1981 Conf Proc ESO Munich

10. SOLAR ACTIVITY (ACTIVITE SOLAIRE)

PRESIDENT: V. Bumba SECRETARY, R. Howard VICE PRESIDENT: E. Tandberg-Hanssen ORGANIZING COMMITTEE: R. J. Bray, M. Dryer, O. Engvold, J. Harvey, G. Newkirk, Jr., M. Pick, D. Rust, V. E. Stepanov, H. Yoshimura, H. Zirin This report summarizes research on solar activity over an almost three-year period from January 1, 1979, till the end of June 1981. In preparing this report we respected the advice of the I.A.U. Executive Committee to cover the highlights of work carried out in the field of solar physics relevant to our Commission, and avoiding double work. Only a limited space was made available for our Commission. Given this restraint we tried to produce a comprehensive review. With great pleasure I appreciate the excellent cooperation of the members of our Executive Committee in the preparation of this report. During the period covered by the present report numerous solar international symposia, colloquia and workshops, as well as several world-wide solar observation campaigns demonstrated the growing importance of the solar activity phenomena for understanding of many astrophysical problems. At the XVllth General Assembly of our I.A.U. in Montreal, the Joint Discussions have demonstrated that the majority of stars in our Galaxy have not only their chromosphere, the transient regions and coronae, but that they also lose their mass due to stellar winds. Recently, for example, during the Second University College London Astronomy Colloquium on "Solar and Stellar Magnetism and Rotation" held in the Cumberland Lodge, Windsor, it has been shown that most of these stars produce magnetic fields responsible for their stellar activities and correlated with their rotational velocities - practically of the same type like the solar one. To give an example - the results reported by R. W. Noys indicate that stellar active regions sometimes grow or decay over timeperiods of weeks to months. For some stars, active longitudes tend to persist over remarkably long periods. These persistently active longitudes are sometimes accompanied by episodes of a more short-lived activity at totally different longitudes etc. For all these reasons we believe that the reviews presented below may be of interest not only for solar physicists alone. 1. THEORY OF SOLAR CYCLE (H. Yoshimura) The ultimate goal for a theory of the solar cycle would be to construct a model that reproduces and predicts every detail of various characteristics of the solar cycle. The model may be in form of a set of equations and its solutions or in form of a computer code. Once such a model is constructed, it must be able to describe time-varying stellar magnetic activities similar to the solar cycle by handling a set of parameters that characterizes a particular star. Present status of our knowledge of the solar cycle is far from this goal. To near this goal, however, basic mechanisms that drive the machinery of the solar cycle are being elucidated one by one and important concepts are being built up. During the three years period reported here, active endeavors have been done along several fronts with different kinds of approximations and simplifications. The concepts deve10ped for the solar cycle are now being applied to understanding of stellar variability (Belvedere et al,AA §§, 240; 91, 328; Stix,GAFD, in press; Durney et al, PASP, in press; Durney and Robinson, Ap J, in press; Robinson and Durney, preprint). Several good monographs related to the problem were published in the period (Krause and Radler, Mean-Field Magnetohydrodynamics and Dynamic Theory, Pergamon Press; Moffatt, Magnetic Field Generation in Electrically Conducting Fluids. Cambridge Univ. Press; Parker, Cosmical Magnetic Fields, Clarendon Press). Various reviews related to 55

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theory of solar cycle appeared in the symposia held in the period on the same and related subjects. In order to understand the diversity of the various opinions and approaches to the problem, we must keep in mind that degree of advancement of one approach, and understanding of the phenomena of a researcher involved in the approach. can be considerably different. A theory, however, which might be regarded as too primitive at its present stage of development, might provide some important concepts to the major advancement of understanding of the solar cycle. A model of the solar cycle must be derived from first principles of physics with given mass, chemical composition, and angular momentum distributions of the proto-Sun. This task is formidable and almost impossible at present since we must trace every detail of motions of various particles and fields. In these circumstances, we start from averaging the basic equations that describe the first principles of physics. Averaging the equations over some macro-space and time (continuum approximations), we get equations of magnetohydrodynamics (MHD) with molecular viscosity and diffusivity. Since considerably hierarchy of scales exists in structure and behaviour of flows and fields of the Sun, we need further averaging process to smooth out effects of flows and fields whose scales are smaller than those we have in mind. The concept of mean magnetohydrodynamics (MMHD) has emerged in such an averaging process. In these conceptional manipUlating procedures. we like to believe that there exists another kind of basic principles that govern macro or global dynamics of the Sun and of any other physical systems. Thus we go in quest of the new kind of basic principles. This is especially important when we study nonlinear self-organization of various kinds of physical systems. The solar cycle with its long-term behaviour is now regarded as one of such nonlinear systems. One front of theoretical research that demonstrates ability to reproduce and predicts various characteristics of the solar cycle to a considerable degree are the dynamo theories. These theories take the standpoint that the magnetic field responsible for the solar cycle is generated by MHD dynamo driven by flows of differential rotation and helical convection. The latter is a conceptional name which represents convection that lacks symmetry with respect to the rotational axis. The theories have been treated by MMHD. The basic question we now have is what kinds of convection inside the Sun actually correspond to the helical convection. One class of theories treats it as turbulent convection assuming that granulation and/or supergranulation correspond to it. This class of turbulent dynamo theories has been criticized by Piddington \Ap J ffi, 293) and Layzer et al (Ap J 229. 1126) mainly on two reasons. First, physical mechanisms of turbulent diffusion in terms of molecular diffusion are not well established. Second, the turbulence and the magnetic flux ropes observed on the Sun are roughly of equal size; MHD interactions between such fluid motions and magnetic fields are highly nonlinear and it is not straightforward to see whether or not the approximations adopted in the formulation of the theories are valid for the case of the Sun. Also, it is not clear whether the turbulence works as a dynamo or as a diffusive medium (Meneguzzi et al, preprint, submitted to PRL). Observations of dispersal of global scale magnetic features in ., 1960's have suggested that granulation and supergranulation work as diffusion media over a long time scale. The other class of theories regards the global nonvection as the helical convection re3ponsible for the dynamo. Long-term efforts have been made to detect its velocity fields on the Sun directly by Doppler effects but nobody has succeeded yet (LaBonte and Howard, SID, 21; Howard and LaBonte, Ap J 2)9, 738; Gilman and Glatzmaier, Ap J 241, 793; LaBonte et al, preprint). The question we have is whether it exists only in the deep part of the convection zone; no suitable method is devised yet though it penetrates to the surface and is observable in principle (Stix, AA 93, ·339). A subgroup of this class treats the problem by an MMHD procedure averaging MHD,.,over longitude and over a time scale long enough to smooth out the effects of individual features rotating with the Sun. The dynamo equations obtained by this procedure are similar to those of the turbulent .c - /oII"dynamos or even to those of the phenomenological Babcock-Leighton model. This subgroup can bypass the criticism against the turbulent 0( - w- dynamos to some degree. The flows of the differential rotation and the global convection are large enough to carry the individual

"-III'

SOLAR ACTIVITY

57

magnetic flux ropes observed on the surface as if they represent conceptional individual magnetic field lines. However, turbulent diffusion is necessary to understand the coherent hebaviou~ of the overall magnetic system demonstrated by the Butterfly Diagrams and Hale s polarity rules of sunspots. Surprisingly, the 0( - wdynamos equations either formulated by the turbulence theories or by the global convection theories can reproduce various characteristics of the observed solar cycle t~an impressive degree. This suggests that the dynamo equations have captured basic processes of the solar cycle and can be a milestone to approach the goal of finding a new kind of basic principles that govern the solar cycle. Major observational aspects of the solar cycle that were studied by the equations during the reported period are the fo11owingl (i) Long-term behaviours of the solar cycle with its hypothetical 80-year modulation and other longer time-scale modUlations with prolonged eras of low state of activity like Maunder Minimum were interpreted for the first time as intrinsic properties of a nonlinear system of magnetic oscillations of the solar cyc1el A new period amplitude relation of the solar cycle was predicted by the theory and verified by an analysis of the sunspot relative number curve (loshimura, Ap J 226,706; 227, 1047). However, the remarkable degree of stability, of the phase of solar cycle oscillations suggests that the hypothetical chronometer of Dicke (N 276, 676; 280, 34; NS 1979, July 12) could be provided. by the nonlinear oscilating dynamo. The properties of the nonlinear oscillations of the solar cycle with its similarity to the geomagnetic reversals were studied using si~p1er systems of equations (Brauer, AN )00, 43; 301, 203; Kleeorin and Ruzmaikin, GAFD 17,281; Ruzmaikin, CAp 9, 85; loshimura, Ap-J ~, 625; Krause and Roberts, ASR 1, 231). (i~) Torsional ;scil1ations of the Sun in close associat ion with the solar cycle (Howard and LaBonte, Ap J 239, 1.83) were interpreted in terms of forced oscillations driven by the solar cycle Lorentz force waves (Yoshimura, J-FS; Ap J 247,1102; Schussler, AA 94, L17). The 11-year period of the oscillations were regarded as an evidence to exclude the possibility that 22-year period oscillating meridional circulations might drive the solar cycle (Weiss, AS). (iii) It was pointed 'out that the present formalism of the .t. - lArdynamos cannot distinguish between dipole and quadrupo1ar parities with opposite and same polarities in the northern and southern hemispheres (Belvedere et al, AA 86, 40). This remains a problem for further research. Theoretical efforts to furthe; the formalism of the turbulent dynamos were deployed ,WaIder et 901, JFM 96, 207; Radler, AN lQl. 102). -Another subgroup of the 0( - ~dynamos undertakes large scale projects to simultaneously solve MHD equations for the flows and magnetic fields associated with the differential rotation and the global convection without averaging over longitude (Gilman and Miller, Ap J Sup 46, 211; Gilman in WCSSSS, in press; Cuong and Busse, PEPI 24,272). However, this subgroup has not reached the point yet to be able to simUlate the solar cycle. In connection with these projects, studies to understand the dynamics of the differential rotation and the global convection advanced (Gilman and Foukal, Ap J 229, 1179; Gilman, Ap J 231, 284; Gilman and G1atzmaier, Ap J Sup 42, 335; Glatzmaier and Gilman, Ap J Sup 45, 351, 381; Geiger and Busse, GAFD, in press). Efforts to determine dynamical structure of the differential rotation in depth and in latitude with different formalisms also advanced (Durney and Spruit, Ap J 234, 1067; Belvedere et al, GAFD 14, 209; Schmidt, Thesis of Univ. of Freiburg):-NO definitive conclusion as to the structure of the differential rotation was reached from the studies yet. Also, an effort to solve the dynamics of the flows and the fields simultaneously within the context of a turbulent ~ - w-dynamo was undertaken ~Schussler, AA 72, 348). These theories also adopt averaging over a certain space and time and revresent the effects of unresolved flows and magnetic fields by turbulent viscosity and diffusion. Thus the theories are a part of MMHD although the equations are similar to those of MHD with molecular viscosity and diffusivity. Among the effects of unresolved features, the dynamical role of magnetic flux tubes in the global dynamics is important. After studies of flux tubes (Schussler, AA 11,79; 89, 26), Schussler (N 288, 150) proposed a simple model of the solar cycle incorporating the role of the flux tubes in the model. He interpreted two of

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the important observational findings in the reported period in terms of the rise time of flux tubes from a fixed layer where the toroidal field is generated and carried to the surface; the anticorrelations of appearance of X-ray bright points (Golub et al, Ap J 1229, L145), and of brightness variations of sunspots (Maltby and Albregtsen, Ap J 1234, 1147; Albregtsen and Maltby, SP 71, 269), with the solar cycle. Contrary to the interpretation in the model, however, ephemeral magnetic regions vary with the solar cycle (Martin and Harvey, SP 64, 93). Similar conjecture but with different interpretation based on the dynamo near the bottom of the convection zone was proposed by Golub et al (Ap J 243,309) on the implication of X-ray bright points and the role of the magnetic-flux ropes. In various different model~, C~khale (KOB A~, 217, 222, 224; Bratenahl and Baum, SID 29; Piddington, AUP 32, 671) studied the role of the magnetic flux ropes in the dynamics of the solar cycle. An iillp:)rtant but controversial issue for the theory of solar cycle is the luminosity and its associated radius and temperature variations. Prior to the reported . period, the theory of the solar cycle was primarily concerned with the origin and evolution of ~agnetic and velocity fields. Since nonlinear feedback of the generated magnetic fields on the convection requires a solar cycle associated modulation of thermal structure of the convection zone, it was expected that total heat flux must vary with the ll-year solar cycle and/or its 55-year ~or 80-year when only amplitude is taken into account) cycle. the latter would be more prominent if the former is smeared out by convective processes (Yoshimura, Ap J 220, 692; 226, 706). Although simple models were investigated using the mixing length theory of convection (Sofia et aI, SC 204,1306; Thomas, N 280,662; Dearborn and Blake, Ap J 237,616; Spiegel and Weiss:-N 287, 616; Gillilan~, N 286,838), it is not clear ye~heoreti­ cally how and to what a degree the total heat flux change occurs and how it manifests itself as radius, temperature, and luminosity changes. In such circumstances, we must rely on observations. Extensive observations and analyses were and are now being performed for radius (Eddy and Boornazian, BAAS II, 437; Shapiro, SC 208, 51; Wittmann, SP 66, 223; Dunham et aI, SC 210, 1243; Dunham et aI, BAAS 12, 832; Parkinson et aI, N 288, 548; Candell, BAAS 13, 559; Gilliland, BAAS 13, 553; Ap J 248, 1144; Howard, preprint), for temperature (Livingston, N 272, 340; White and Livingston, Ap J 226, 679; Ap J, in press; Livingston and Holweger, preprint submitted to Ap J)-;;d for luminosity (Foukal and Vernazza, Ap J 234, 707; Willson et aI, SC 207,177; Willson et aI, SC 211,700; Willson and Hudson, Ap·J 244, L185). Especially, Parkinson et al (N 288,-s48) and Gilliland (Ap J 248, 1144~ound evidence that the solar radius might have undergone an approximately SO-year periodic variation. Further studies are needed to establish facts and the theory of solar cycle is now entering a new era of development. 2a. EMPIRICAL ASPECTS OF THE SOLAR CYCLE (R. Howard) Observational studies of a long series of Doppler velocity data over the solar disk (Howard and Labonte AP J L 239, LJ3; SP 74, 131) have shown that the rotation rate increases and decreases in latitude zoneS-which drift slowly equatorward. At any time there are two pairs of such zones in the northern hemisphere and two pairs in the southern hemisphere in symmetric patterns. The zones, which originate near the poles, drift to the equator in a period of about 22 years. At anyone latitude, the period of this torsional oscillation is about 11 years. A fast zone originates at each pole near the minimum of the solar activity cycle, and ~ slow zone originates near maximum. The amplitude of this effects is about 3 m s- • Solar activity is centered about the shear zone of th~s torsional pattern between a fast zone and the adjacent slow zone in the poleward direction. This leads to the conclusion that the torsional motions are in some way associated with the activity cycle. The amplitude of the shear shows little or no variation over its 22-year lifetime. As the waves move to the equator they become thinner in latitude extent. A one-per-he~sphere torsional wave in the rotation rate has also been found. This

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is not a travelling wave. It has a half-amplitude of about 5 m s-l. The high latitudes rotate fastest at solar maximum, and the low latitudes rotate fastest near solar minimum. A study of the large-scale distribution of magnetic fields and magnetic flux over the solar cycle has shown some fundamental properties of the cycle (Howard and Labonte SP 1!, 131). During the cycle the sunspot latitudes are characterized by average magnetic fields of the preceding polarity. Following polarity fields from time to time stream poleward to form the polar fields. This poleward flow is episodic, not continuous. This streaming motion appears to result from a directed flow, not from diffusion. Results from weak fields on the solar surface show a similar result except that the predominance of preceding polarity fields at activity latitudes is not so pronounced. The polar magnetic fields of the sun have reversed polarity - the northern fields changed from positive to negative polarity in the spring of 1980, and the southern fields changed from negative to positive polarity in the autumn of 1980. T + The total surface magnetic flux of the sun (F '"' IF + IF-I) shows remarkably little variation from activity minimum to maximum. The variations in solar cycle 20 was about a factor 2 and in cycle 21, it was a factor 3. The flux increase per day is about a factor 10 lower than the measured flux, whiCh means that it would require about 10 days to generate the flux we see at the surface on any one day. This rRtio is relatively constant throughout the cycle. This means that magnetic flux disappears from the solar surface at a remarkably fast rate. Practically all the ~etic flux seen on the sun is at the active region latitudes (which is where it appears and disappears). The polar fields constitute only about 1% of the total surface flux of the sun.

I

2b. EJlPmICAL ASPECTS OF THE SOLAR CYCLES (M. KopeckY) Yajor attention was paid to solar activity forecasting. The range of these problems was a special topic of two significant international events, 'Workshop on Solar Terrestrial Predictions" in Boulder (ST.Pp) and the "lOth Consultation of Solar Physicists from Socialist Countries" in Potsdam (PSP 16 and II). 01 and 01 (IAN 80, 12, 2569) outline a new approach to solar activity prediction, based upon the relationship between yearly mean values of geomagnetic activity in the given II-year cycle and during the next solar cycle maximum. Moreover, these problems were dealt with by a number of authors like Simon (SP 63, 399), Vitinskij (SDB 1980, ~, 103 and 4" 104), Lomb and Andersen (MN 122, 723), Meyer (SP 70, 259) and others. A series of papers develop methods for prediction of solar activity based upon its external conditionality (Vasilyeva et al, STPP l, A45; Romanchuk VKU 22, 34; ~ (in press». An evaluation of the reliability of solar activit~ forecast was published by Vitinskij and Rubashev (IGAO 196, 3). According to Kopecky (BAC 11,1), at the beginning of the next century a high level of solar activity may be expected, with values at 200-300 of the maximum Wolf's relative number of ll-year cycles. The interest remains centered, however, on the problem of Maunder's m1n~mum. The ascertainment by Eddy et al (SP 46, 3), who claimed a higher angular rotation velocity at the solar equator in the epoch of Maunder's minimum was questioned by Aberbanel1 and W8h1 (SP lQ, 197). Different aspects of the Maunder's minimum are treated by Schove (SP 63, 423), Romanchuk (SDB 1980,2,103), Gleissberg and Damboldt (JBAA 89, 440), Siscoe (JGR 81, 6224). The same problems motivated also the studies of Clark and Stephenson (QJRAS 19, 387) on an interpretation of the pre-telescopic sunspot records from the Ori~t. Iskhanov and Vitinskij (IAN 284, 577) investigated the long-term variations of solar rotation for the past three years on the descending branch and in the maximum activity phase. At a maximum of the cycle, differential rotation is greatest in those cycles, where the maximum is highest, while prior to a minimum, rotation is

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smaller for those cycles, for which in a subsequent cycle the activity maximum is higher. This occurred also during the Maunder minimum period. From the distribution of 7000 flares with respect to IMF sector boundaries Le~itsky (IKAO 62, 148) demonstrated that in the ascending phase and near the maximum of cycles 19 and 20 there is a stable concentration of flares at the sector boundaries (-, +). The eighty-year period in short-lived sunspots was investigated by Ringnes (RITA 52). Kuklin confirmed (BAC 32,224) the existence of two sunspot group populations and described their behaviour in 80-, 22- and ll-year cycles. A number,of studies dealt with various aspects of the II-year cycle. Latitude drift (Sporer s low) of different phenomena was investigated by Chistiakova and Chistiakov (MP 1981, 41) and by Brown and Evans (SF 68, 141) who studied also the periodicity of the faculae (SF 66, 233). The II-year cycle in the solar corona and solar wind was studied by Rusin et al (SF 61, 301), Waldmeier ~SF 70, 251), Simon (SF ~, 399), Legrand and Simin (SF 70,173), Hundhansen (RGSF 17,2034) and Tritakis (SP 63, 207). Manifestations of the cycle were also found in the variation of the sunspot intensity in the spectral region - 0.387 - 2.35 pm - by Albregtseen and Maltby (SP 71,209), in the far-infrared temperature minimum - Muller et al (AA 87, IJ) and in the solar flux in the far ultraviolet (1l75~100A - by Cook et al JGR85, 2257). According to Singh and Bappu (SP 11,101), the calcium network cellular di;:' meters appear to be by 5% smaller at the solar maximum compared with the minimum. Godo1i and Marracconi (SP 64, 247) and Balthasar and Wahl (AA 92,111) studied the changes of the solar diffe;entia1 rotation in the solar cycle in relation t? the sunspots. See also Proceedings of the Symposium "Study of the solar cycle from space" (NASA). According to Kopecky et a1 (BAC 31,267), the fundamental observational series of sunspots (Greenwich, Zurich, Pulkovo) are not homogeneous if mutually compared; the authors point out some inhomogeneities within the series. The same results were obtained by Vitinskij (SDB 1979, ~, 96). 3. ACTIVE REGIONS (H. Zirin) In the past three years an unprecedented level of observing active regions took place in connection with the Solar Maximum Year, Flare Buildup Study and the Solar Maximum Mission. Although considerable ana1ynis of these data has taken place, little of the material has reached the journals. We have developed, through international cooperation in the study of many of these active regions, a good picture of the buildup of stress in various regions through flux emergence and its gradual release through the flare process. The proceedings of the Sky1ab Workshop on active regions, held in 1978-79 shoul,~summarize work in this field up to 1979 but unhappily are still with the printer. They will be an important milestone in this field. A. Small Scale Fields There has been continued interest in the structure of small scale magnetic , fields but little new data. Although most workers are in agreement on the idea that fields are concentrated in knots of strong field evidenced by the filigree network, evidence of the actual field strength is still indirect. Tarbell et a1 (Ap J 229, 38'7) 'studied high resolution filter magnetograms and fitted their data with elements of average field strength 1200g. covering .085 of the p1age area; however their data could also be fit on the assumption that their half arc second resolution resolved the field structures, which then had average field 280 gauss and covered .36 of the area. Despite the difficulties of detecting them there has been considerable analysis of the possible properties of the tiny flux tubes. Knobloch (Ap J L247, L93) and Knobloch and Rosner (Ap J 247,311) have discussed the way small scale magnetic features are generated by turbulent convection. Knobloch argues that for scales

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below a cutoff, further concentration cannot take place. It is not obvious how the eddied maintain the unipolar character of the network fields. Spruit (SF 61, 363) and Spruit and Zweibel (SF 62, 15) analyzed the stability against magneti~buoyancy of flux tubes and found these to be stable for beta (ratio of gas to magnetic pressure) above 1.8, which means that photospheric tubes with fields above 1350g are stable. Stellmacher and Wiehr \AA 75,263) analyzed the center to limb variation of filigree contrast and found it could be fitted with the Koutchmy-Stellmacher model, in which the bright walls of the flux tubes produce the desired effect. Caccin and Severino (Ap J 232,297) arrived at similar conclusions; there are enough free parameters in these unobservable structures to make good fits possible. Chapman lAp J 232, 923) designed a new facular model which supports the "hot wall" picture. B. Ephemeral Active Regions There has been continued study of the interesting ephemeral regions and their relatives, the X-ray bright points. Golub et al (Ap J 1229,1145) find the number of X-ray bright points to vary inversely with the solar cycle, while Martin and Harvey (SF 64, 93) found the number of ephemeral regions on magnetograms to vary with the cycle. Martin and Harvey found the rise in ER activity to procede the rise of the cycle by at least a year; if new cycle ER were separated, the}r data showed the ER essentially matching the rise of the cycle. They found the ER s to generally show the correct polarity in equatorial latitudes and what may be called new cycle polarity in higher latitudes. The contradiction between the X-ray and magnetographic observations a~pears not to be a threshhold effect; Golub et al (SF ~, Ill) found at least half the bright points to match ephemeral regions and the discrepancy is far too large to be explained by factors of 2. , These papers do agree that the fraction of flux emerging in ER s is large, far greater than that in active regions. Of course this flux is in small dipoles which disappear and hence cannot contribute much to the general solar field. Marsh (SF ~, 105) has argued that bright point flares can provide enhanced diffusion of magnetic fields by reconnection and thus play an important role in the cycle. Golub et al (Ap J 243,312) have argued that the ER's must be generated in a subsurface region shallower than the source of active regions and be spread into the chromo spheric network by the supergranulation flows. This picture would lead, however, to a b}polar network, while the observed network is unipolar; in addition films of ER s show little if any flow influenced by ,the network. C. General Active Region Studies Despite the high level of observing in the last years ~or perhaps because of it) there has been li ttla published materia~_ en classical activu regions except for analyses of UV data. Baranovsky and Severny (IKAO 50, 99) made a new model based on data in the UV lines, especially Ly alpha and beta. They found enhancements of density and temperature of about one order of magnitude relative to the quiet sun transition zone. But to explain the Ly alpha and beta intensities they required a thin ('" 300 meters) hot layer with densities of 10 (exp 13). Baranovsky and Stepanyan (IKAO 60,135) analyzed line intensities in UV and visible in stable plages and found, in contrast to growing plages, that intensities at higher levels were well correlated with those in lower chromosphere lines (H alpha or Ca K). Levine and Pye (SP 66, 39) studied the temperature structure in active regions on the basis of Skylab data, deriving differential emission measures for the different regimes. They found emission measures of 3 exp 48 cm (-1) and radiative losses of 4 exp 26 ergs/sec above 100,000 deg. Kahler (SF 62,347) studied the preflare X-ray characteristics of active regions and found no evidence for pre flare heating; in most cases flares occurred in points which were not the brightest in X-ray. Microwave observations show the same general result: the flare source is displaced from the previous source, although not very far.

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D. Microwave Mapping Microwave ~ bservations with high resolu tion radio arrays are beginning to reveal the ~gnet~c and coronal structure above the active region; much of this work was sUmm&r7zed b~ Schmahl (~~, 71). In general the results correspond to those from ~-ray stud1es.by Webb and Z~r~n (SP 69, 99) who found bright coronal loops ending 7n hot. spots ~n the penumbra or other regions of emerging flux, and that the peak ~ntens1ty was always over neutral lines. Radio results lKundu et al AA 82 265' Lang and Willson BPS, 109) show a single core of emission centered on a-n;utrai line, with peaks o~ circular polari~ation. These authors derive rather strong fields lup to.900 gauss) ~n these such reg~ons, much stronger than force-free calculations. Gelfre1kh.and Bogod (SP 67,29) by contrast, find 40 gauss from polarization measures. St 7ll, the observed radio require the fairly large fields, so there is a problem e~ther way. The active regions are sufficiently complex that it is not completely sure where the radio sources fall. The development of high resolution microwave arrays and spectrometers offers hope for the detection of current sheets and evaluation of the importance of gyroresonance absorption in the n0n-flaring active region lZheleznyakov and Zlotnick BPS, ff7). E. Emergence and Decay

The process of emergence and decay of active region fields is one which deserves more attention. We know that field emerges through the emergence of flux loops marked by arch filaments. The decay process has been less closely followed. Models of the sunspot cycle have assumed they decay by outward diffusion of their fields, but optical observers have not seen any such behaviour. Howard and Wallenhorst (SP 1982) observed 25 decaying active regions at Mt. Wilson and found no increase in the surrounding field regions as they dexay, the flux simply fades away. On the other hand there is also no sign of submergence of the field, which would be marked by close approach of opposite polarity to the neutral line. If the flux were concentrated in small tubes which spread it would still be detectable by the magnetograph. The problem is intriguing.

F. The Sunspot Energy Deficit It has long been felt that the energy which is suppressed by the sunspot phenomenon must escape the sun in the surrounding areas, in fact early mo.dels of active regions used this concept. Simultaneous data from two orbiting radiometers on the Solar Maximum Mission and on Nimbus-7 gave for the first time reliable data on these effects. The radiometers measure all energy outflowing with high accuracy. Willson et al (Sc 211, 700) and Hickey et al (EOS 61, 355) both found that small changes in the solar constant correspond to th;-sunspot area less the contribution from white light plages near the limb. Thus the missing flux never gets out and theorists are busy with post hoc explanations. Our picture of the convective phenomena underlying an active region will surely change.

4. SUNSPOTS (V. Bumba)

Major progress during 1979-1981 has been made in the observations of individual sunspot fine-structure elements and their interpretation. The problem of a single large magnetic flux tube farming the sunspot umbrae has been replaced by the study of a model of a dynamical clustering of many separate flux tubes pushed together due to various, but before all convective forces. A renaissance of sunspot spectral observations seems to be seen in

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the growing importance of various ground-based as well as space spectrographic observations. A. Observations of Various

Fine~Structure

Elements

Interesting results have been obtained in the study of the sunspot bright umbral dots. It has been demonstrated by several groups of observers that umbral dots virtually cover the umbra, including the darkest regions of large spots, where the low contrast of the dot pattern has hitherto hindered its observations (Lougbhead et al, AA Xi, 128). Each sunspot umbra, regardless of umbral size, magnetic field intensity, darkness, form, age and presence of a penumbra has an identical internal m~rphological structure and the character of this internal umbral structure does not change during the whole process of spot development and does not depend on the phase of the solar activity cycle either (Bumba and Suda, BAC 11, 101). Th~ area covered by the bright fine umbral features takes, as a rule, about 10 - 5% of the total area of the umbra (Abdussamatov, SDB~, 99). Even two types of these bright features seem to exist (Sattarov, MPSA ~f 107). The life-time of the greatest part of them is longer than 30 minutes, some of them live for several hours (Sattarov, MPSA~, 122). . An extensive discussion concerning the problem of a J'morphological similarity" between the umbral fine structure and the photospheric granulation has been published by the qhoted authors, as well as by Adjabshirizadeh (OR 290, 541), Adjabshirizadeh and Koutchmy (AA.§2., 88; AA 99, 111) giving ideas about the denSity of the umbral bright points distributions, their sizes, contrast value, brightness temperature etc. Sattarov (AZ 21, 610) succeeded in finding some new information concerning the magnetic field action on magnetic sensitive spectral lines in the dark and bright fine structure elements in some sunspot umbrae. He found that near the center of the solar disk the lines Fe I 6303.499 A, Ti I 6064.626 A, Or I 5781.759 A show the doublet Zeeman splitting in the bright umbral dots and the triplet Zeeman splitting in the dark umbral regions. In the dark regions the intensity of the ~ -component of the line Fe I 6302.499 A is greater and in the line Or I 5781.759 A smaller than the intensities of their r-components. It is shown that the appearance of the strong ~ -component in the edge zone of the umbra may be partly due to the blurring effect. Some theoretical interpretations have been given by Obridko (SDB~, 101) who demonstrates that the properties of bright umbral elements are not in agreement with the characteristics of a free oscillatory convection. Instead of it a new mechanism of forced oscillatory convection is suggested. This idea seems not to be far from the Parker's conception (Ap J l2i, 333), following which the subsurface magnetic field of a sunspot splits into many separate flux tubes, with field-free gass between. The field-free ·columns occasionally punch their way up through the overlying magnetic field to the surface, where they appear as the bright, field-free umbral dots. The fine structure of light bridges in suns ports has been studied by MUller (SP~, 297) on high resolution photographs, obtained at the Pic-du-Midi Observatory, and an attempt to estimate their types following their morphological details in umbra, penumbra and photosphere has been made. A very detailed description of two types of sunspot light-bridges evolution in the large August 1972 sunspot group and their dependence on the magnetic field polarity distribution is given by Bumba and Hejna (BAC 11, 257): the normal photosphere-like light bridges formed from chains of bright granules separate the umbrae or their parts of the same sign of magnetic field polarity\ the light bridges formed from elongated penumbral-like fibrils are closely related to the boundary between the two opposite polarity fields. Zirin and Moore (SP~, 79) found a new morphological feature associated with the outer edge of the penumbra of a small spot in a large complex spot group, a small continuum bright point. They call it" penumbra-periphery bright

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point" • Parfinenko (SDB 80, 85) studied the structure of light rings around sunspots using high-quality stratospheric and ground based sunspot observations and a new TV method. He claims that the outer light ring is formed by a relative clustering of bright photospheric granules bordering with the sunspot penumbra and that the inner light ring is formed by the ends of light fibrils of the penumbra. In his view these light rings are observed in all developed sunspots. Grossmann-Doerth and Schmidt (AA 95, 366) analysed a series of "white light" images of sunspots taken under-Very good seeing conditions at Izana (Tenerife) to derive the brightness distribution of sunspot penumbrae. B. Spectral Observations From observations of the French (l.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region it was estimated (Kneer et aI, SP ~, 289) that the behaviour of the emission cores of the Ca II Hand K and Mg II h and k resonance lines is very similar and the correspondence in the intensity between the four lines persists in quiet Sun, umbra, penumbra and plage. The relation between the Ca and Mg emission is slightly non-linear; this must be attributed to a different response of Ca and Mg to atmospheric structure. Umbral profiles show no self-reversals but asymmetrics from which the authors infer the presence of velo~ities, either oscillatory or stationary, with amplitudes of about 5 kID s • The emission above sunspots lacks correlation with both Ca or H" emission. The LtC profile directly above the umbra was found narrower and of higher intensity than in the quiet chromosphere. The electron density in the Lee: forming layer and temperature was estimated. Kollatschny et al (AA~, 245) demonstrate that the wings of the infrared Ca II lines depend in upper atmospheric layers sensitively on the temperature gradient but not essentially on the absolute value of temperature. It was observed that these lines remain almost unchanged from photosphere to umbra and are thus sensitive to paraSitic light. It is shown that the conflict between the model calculations and the observed lines may be removed by adopting an opacity enhancement as introduced by Zwaan in 1974. Firstova (AZ 21, 666) shows that the ratio of maximum intensities of the Hand K Ca II lines between "quiet" portions of an umbra and umbral flashes is practically equal which may indicate a possible equality of the optical thickness in both umbral features. Observations with an out-eclipse coronagraph and an image tube confirm the presence of the enhanced He I 10830 A line in the sunspot umbra spectrum. A qualitative difference between the profile of this line in the umbral spectrum and a plage spectrum has been found (Borodina and Papushev, PAZ 2, 620). The umbral brightness temperature has been determined from observations by Sitnik (SDB 80, 99) for the spectral range of 4800-21000 A. The author estimated that in this spectral interval the continuous absorption due to the existence of H- really dominates in the umbra, but is smaller than in the photosphere. For shorter wavelengths a new continuous absorption agent exists. It causes increase of additional opacity with decreasing temperature. Several new identifications of molecular lines in the EUV spectrum of sunspots were reported, as for example emission lines of the CO (Jordan et al,NN 187, 473), and new molecular hydrogen lines representing fluorescence from the Werner bands, found for the first time in the solar atmosphere (Bartos et aI, MN 187, 463). An analysis of 147 pure TiO lines in a high resolution sunspot umbra spectrum suggests that coherent scattering is more likely than LTE for the formation process of the studied lines (Boyer, AA Sup 40, 277). The presence of several molecular absorption band systems (mostly in UV) umbral spectra had been examined: O2 (Joshi et aI, SP ~, 79), MgO (Murty SP 63, 8J), SiO (Joshi et aI, SP 62, 777. It has been shown that bound-bound opacity due to electronic transitions of molecules CN, CaH, MgH

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and TiO explains in a first approximation the line haze opacity postulated by Zwaan for the near infrared umbral spectrum (Gaur et aI, SP 62, 83). In the same wave-length region the molecular opacity seems to dominate the opacity due to the negative hydrogen ion (Jo~2i eS ~l, SP~, 255) in the higher layers of the umbral atmosphere. The ~ - ~ IR system of the CrH molecule has been identified in the spectrum of a large sunspot (Engvold et al y AA Sup j,g., 209). The relation between the pressure and content of molecules in sunspots has been calculated using the LTE solution of the dissociative equilibrium equation for a set of sunspot models (Stefanov, VKU ~, 39). C. Magnetic Fields Only few new observations concerning the sunspot magnetic fields were published. Ye et al (AAS 20, 275) devoted their paper to the method of determining the gradient of-magnetic field using the asymmetry of the profiles and the rotation of the wings of Zeeman components. Gurman and House (SP 71, 5) used observations of a round, unipolar sunspot in the Fe I 6302.5 line with the HAO Stokes Polarimeter to derive the vector magnetic field in the sunspot. They also demonstrated oscillations of the umbral field magnitude at a period of 180 s. Landi Degl'Innoventi (SP~, 237) interpreted linearly polarized intensity distributions observed in sunspot's with the Marshall Space Flight center's vector magnetograph taking into account magneto-optical effects. It is shown that these effects can be responsible for the observed spiral configuration in the pattern of linear polarization, even if a purely radial, oonvectional sunspot model is used! Makita (PASJ 11, 575) developed a method applying the theoretical solution of the radiative transfer problem with the magnetic field to the observed Zeeman line profile. The assumptions of a pure-absorption atmosphere and of no magneto-optical effect allow a model-free determination of the magnetic field averaged along the optical depth. The method is applied to a penumbral spectrum. Similar problems of radiation transfer through a model sunspot under a variety of conditions for a ray emerging from a typical penumbral point are solved by Landman and Finn (SP ~,221). The first phases of the sunspot magnetic fields formation were studied by Bumba (BAC 32, 129). D. Motions stellmacher and Wiehr CAA 82, 157) attempted to derive a model of the velOCity field of a sunspot penumbra from both spatially unresolved and resolved spectra. The profiles of lines with small Zeeman splitting were observed by them in penumbrae at various heliocentric angles 9. Spatially unresolved spectra show decreasing shifts of the line cores and increasing line asymmetries with height. It was shown that a decomposition of the asymmetric profiles into a main component and a satellite yielded contradictory results when considering the depth dependence and the center-to-limb variation of different lines. Conflicting velOCity gradients were deduced from the line asymmetries and the core shifts. The lines Ti I 5222.7 and Fe II 5264.8 were observed in a sunspot penumbra et cos 9 = 0.7 with a spatial resolution of about 2.5 arc s. It was found that the line widths, residual intensities and asymmetries in bright as well as in dark spectral streaks increased with increasing line shift, although in bright regions the profiles were less shifted and more asymmetric. Some model calculations were made. Surkov and Surkova (AC 1058,3) investigated the sunspot profiles of the non-magneto-active line Fe I 5576 •.10 A; they seemed to succeed in explaining some observed details of the line profile as a result of the large local motions. Shibata (SP j&, 61) explains the repeatedly observed strong downdrafts

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in photospheric lines of young sunspot and pores as due to the sliding matter along the rising magnetic flux tubes. Abdussamatov (SDB ~, 93 and SP i2, 197) found that the Evershed flow observed in the lines Fe I 6302.5 A and in the H~ was almost parallel to the solar surface. Baranov and Lazareva (SDB~, 96) demonstrated that in the largest part of the sunspot umbrae of the group studied by them during the whole period of_~bservations the downward motion of matter with a mean velocity of 0.2 Jan s was observed. Rassulov (SDB]g, 74) in his study of the velocity field in the H« chromosphere above a sunspot shows that these motions are complicated and that the inflow of the material into the spot prevails and the measured velocities may be found mainly inside the plage. Obridko (SDB~, 96) demonstrated that the existence of an insulating boundary shell around the sunspot umbra, protecting it from the overheating, required an upward flow of the matter along this shell which would be afterwards transformed into the Evershed motion. E. Umbral Models Baranovsky and Stepanyan (IKAO 62, 125) derived empirical models for 20 sunspot umbrae using the wings of the K Ca II and D Na I lines. Five of these models represented the development of one spot durifig the period of 8 days. It was found in this developing spot that at first the temperature changed scarcely, but the density decreased; after that both the temperature and the density increased. The density changes reached nearly the value of one order. In general, the large dark spots revealed a tendency to a lower density. Umbral models with enhanced continuum opacity were studied by Stellmacher and Wiehr (AA 22, 229). Clark (SP 62, 305) investigated simple thermal models of sunspots based on the concept of partial inhibition convection by strong magnetic fields. Two specific results of his study might be mentioned: deep spots shoul.d produce weak bright rings in the surrounding atmosphere, whereas shallow spots should produce intense rings which would be difficult to reconcile with observations. Only a surface layer of a spot, with thickness of the order of the temperature scale height, was cool. Parker published an extended series of papers called Sunspots and the Physics of Magnetic Flux Tubes. In the first paper (Ap J ~, 905) he reviewed the current state of the sunspots theory and concluded that a single large magnetic flux tube could not have the properties exhibited by a sunspot. In his new model the sunspot appears as a dynamical clustering of many separate flux tubes, pressed together to form a single flux tube at the visible solar surface, but othervise distinct and separate within the interior of the Sun. In the following paper (Ap J 12Q, 914) he studied the aerodynamic drag on a slender flux tube stretched vertically across a convective cell, which might push the flux tube into the updrafts or into the downdrafts, depending on the density stratification and the asymmetry of the convecting fluid motions. To account for the observed strong cohesion of the cluster of flux_ l tubes that make up a sunspot, he proposes a downdraft of the order 2 kID s through the cluster of separate tubes beneath the sunspot. He also investigated the aerodynamic lift on a rigid circular cylinder in a nonuniform free stream and applied the obtained results to the motion of flux tubes in the Sun (Ap J ~, 250). The calculations of Tsinganos (Ap J ~, 260) established that a long circular cylinder immersed in a convective flow pattern in an ideal fluid is pushed out of the upwellings and the downdrafts of the convective cell into a location midway between them. Parker also demonstrated (Ap J 231, 270) that parallel tubes in a uniform flow are attrached or repelled depending on whether they are side by side or one ahead of the other, respectively. A pulsating or undulating tube attracts all other neighbouring tubes toward itself. He also showed,(Ap J ~, 282) that a cylinder moving in an ideal fluid was subject to convective instability and propelled forward in its motion by the convective forces; this convective propulSion acting on magnetic flux tubes in the solar convective zone was comparable to the forces

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of magnetic bu,~yancy, aerodynamic lift and drag exerted on the tube. In its seventh paper of the series (Ap J £J£, 291) Parker found that the downdraft postulated to operate beneath the sunspot to account for the gathering of flux tubes to form the spot, would be sufficient to reduce the heat flux to values comparable to those observed in sunspot umbrae. Moreover, the overstability in a magnetic field in a downdraft (Parker, Ap J ~, 1005) as well as the hydrodynamic instability of the buoyant fields (Tsinganos, Ap J ~, 746) were considered. Low (SP 67, 57) described a method for generating exact solutions of magnetostaticequilibrium describing a cylindrically symmetric magnetic flux tube oriented vertically in a stratified medium. F. Energy Transport and Oscillations New measurements of the radiative flux deficit of two large sunspots, based on detailed isophotometric maps, were18resented by Bra~O(SP ~, 2~' !~e umbral and penumbral deficits were 4-5 x 10 and 1-1.5 x 10 erg cm s respectively. Over limited areas centered on the umbral cores the deficits amount to 76 and 80% of the photospheric flux. Albregtsen and Maltby (SP 71, 269) found significant intensity differences between umbrae of large sunspots, which might be explained by a systematic variation in the umbral temperature throughout the solar cycle. At the same time no center-limb variation in the umbra-photosphere intensity ratio was detected. Both authors (Ap J 1234, L147) presented an evidence for a possible link between the infrared intensity of large sunspots and the occurrence of X-ray bright points. This might indicate a more general reason of the found regularities. Margolis and Knobloch (MN 193, 345) solved the equation of heat transport for the case of a cylinder with a given thermal conductivity imbedded in an otherwise uniform medium with different conductivity. Obridko (AZ 56, 67) tried to introduce a new two-component model of the atmosphere above the-Sunspot to get an agreement of the optical, radio, UV and X-ray observations above the sunspots. Nye and Hollweg (SP i&, 279) considered the propagation of Alfven waves in a simple model of a sunspot. They find that the observations of non-thermal motions near the temperature minimum and in the corona are both consist 7nt wi!~ ~~ upward-propagating A1fven energy flux denSity of a few times 10 erg cm s ,which is too small to cool the sunspot, but is large enough to supply the energy requirements of the transition region and corona above a sunspot., Mullan (SP 1Q, 311) proposes that Alfven waves may contribute significantly to prolonged energization of proton-flares in which umbral coverage occurs, due to the readier access of umbral Alfven waves into the corona above the sunspots because of the lowering of the transition region between the chromosphere and corona in the umbral flux tubes, Zhukov (SDB~, 83) studied the excitation of gravitational waves by Alfven waves in which the observed rapid decrease of Alfven waves flux with the height over the sunspot may be associated with the transformation of a part of Alfven waves energy into the gravitational waves energy. Schener and Thomas (SP 11, 21) identified the umbral oscillations as a resonant response of the umbral atmosphere to forcing by oscillatory convection in the photosphere. From a numerical solution of the full, linearized equations for magnetoatmospheric waves in a detailed model of the umbral atmosphere several new features of the mation follow. Antia and Chitre (SP ~ 67) examined the magnetoacoustic modes excited in a thermally conducting polytropic fluid layer in the presence of a vertical magnetic field with a view to classify them by means of phase diagrams. Teplitskaya et al (PAZ~, 46) discussed the spectroscopic observations of radial velOCity and brightness oscillations in the sunspot chromosphere, Zhugschda and Locaus (PAZ~, 44) considered a model of 180 s. oscillations in the chromosphere above the sunspots to determine its temperature gradient

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as well as the temperature and effective thickness of the temperature minimum from. observed periods of oscillations. G. Radio Emission A model for sunspot associated radio emission at 6 cm wavelength has been constructed by Alissandrakis et al (AA 82, JO). The calculations are in good agreement with the high resolution observations of the same sunspot region at 6 cm, made with the Westerbork Synthesis Radio Telescope. Comparison of the 6 cm total intensity map with D3 , Hand K Ca II spectroheliograms shows that the maxima of the 6 cm emission correspond to the location of sunspots (Erskine et al, AA 8J, 256). It has been demonstrated at the Crimea Observatory (Dommin et al, lKAO ~, 176) that the degree of left- and right-handed polarization of S-component sources related to the sunspots show dependence on the strengths of the appropriate spots magnetic fields. In papers by Akhmedova and Rybakov (SDB 80, 85), Gelfreikh and Lubyshev (AZ 2&, 562) new sources models for cyclotron-radiation above sunspots have been constructed. 5. PROMINENCES (0. Engvold) I. Introduction The proceedings from the IAU Colloquium No 44 (PSP) contain comprehensive reviews of prominence research. Important publications on the physics of active (flare associated) prominences are included in the SF, Chapter 7, by Rust et al and in the SID. New observational and theoretical studies have addressed the familiar questions about the magnetic field configuration which must accommodate prominence formation and the subsequent provision for support and heat shield. Classical magnetostatic models in thermal equilibrium have been elaborated. Simplified dynamical models for quiescent prominences have been advanced which present interesting perspectives. The combined use of X-ray, EUV and radio data have provided better knowledge about the P-C interface region and the associated coronal cavity, which are essential for understanding the mechanics and thermodynamics of quiescent prominences. Continued stUdies of the P-C transition zone and the immediate prominence enVironments, possibly with emphasize on good spatial resolution, should be encouraged. II. Quiescent Prominences a. Thermodynamics diagnostics. Kanno et al (SP~, J13) have studied the H I LyC emission in quiescent prominences and reported slightly higher optical thickness (t' 2> JO) than given in earlier works. The hydrogen ionization was < 50% ~! the central parts and appeared to increase towards the periphery of the prominences. Sitnik (SA £i, 584) derived a noticeable centre to edge decrease in the source function of subordinate Balmer lines. Lhagvazhav et al (SDB 12/74 and SDB 1/88) have investigated the radiative transfer of the resonance line ~ 584A and the continuum at ~ 5041 of He I in prominences and found the source functions to depend strongly upon the H I LyC opacity. Taking prominence fine structure into account :Rfral.J:3 and Schmahl (Apj 240, 908) inferred T =7700±800K and 11 > 2,.2 10 -em from LyC analysis of several prominences. :6ased on optically thin lines emissio~h in 3 the visible and IR Landman (ApJ ill, 988) derived T =JOOOK and N ~ 10 cm-, a!!f using the corresponding line widths he got T=6620-1800~and ~t=5.1~1.4 km s • Fontenla (SP 64, 177) derived T=6400K and V t =5.7 kID s • Measurement of

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stark broadning on high quantum number Balmer lines yields usually the highest values for N (Ruzdjak, POS~, 209). Beigman (SA L 2, 27) points out that transi tions .l5. _ n-l (n > 10) of hydrogen at sub-millimeter wavelengths may be observable in prominences and be useful for thermodynamic diagnostics. The fact that some prominences'exhibit centrally reversed lines (Ca II H, K and H~ ) implies local variations of their thermodynamic conditions. Kubota (PASJ ~, 359) found that the central reversal was not correlated with line opacity as predicted by a homogeneous layer model, and concluded that the central absorption arises from 'cooler' optically thick (?:~5) layers near the surface of the emitting structures (cf 6hman, ApJ ~, 97). The 9ccasionally observed branching of particular line ratios (f inst Ca II vs Balmer lines) is due to local variations in the nonthermal velocities according to Stellmacher and Wiehr (SF 71, 299). Landman and Mongillo (SP..§J., 87) measured significant interprominQnce variations in the Balmer decrement (Texc=llOO-3450K). Unresolved local variations of temperature and turbulence are inferred from enhanced line wing emissions (Landman, ApJ ,ill, 988). The implications of spatial variations on thermodynamic modelling, particularly on a sub-arcsec scale, have been considered earlier. Equally important may possibly be temporal variations which may lead to non-stationary radiative conditions (Engvold, SP 67, 351). Sporadic observations of condensation-like processes (Mikhailutsa,SDB'12/85) and local impulsive events (Malville and Toot, BAAS 12, 504) encourages more systematic investigations of changes on short time scale. Jensen (SP (in pr 1981» points out that the small scale random motion of quiescent prominences has the character of MHD turbulence. He notices that supersonic velocities are reached in some cases only, which has serious implications as to local dissipation of energy via effects of compressibility. b. Magnetic fields. The astrophysical use of the Hanle effect for magnetic field determinations have been investigated further by several groups (Bommier et aI, AA 1QQ, 231; Gopasyuk, IKAO~, 108, Landi Degl'Innocenti, SP (In pr 1981». The total magnetic field vector may be derived from linear polarization measurements in two lines. The easily accessible pair D and H« has limited application due to effects of H" line opacity (Lero~, SP 71, 285). Bommier et al concluded from using D and A108]0 ! (cf Smartt and House, BAAS 11, 409, Lindsey and Mickey, BAls 11, 409) that the angle between the magnetic field vector and the long axis-of a quiescent prominence is the range 0 0 _20 0 , which is in agreement with earlier magnetographic measurements. c. Magnetostatic models. Lerche (SP 6], 3) has shown that the thermal balance of prominence matter in magnetostatiC-models is susceptible to thermal pulses from the corona. The shear of the magnetic field is essential for the thermal equilibrium of prominences in regulating the thermal conduction (Milne et aI, ApJ ~, )04). Low (SP (in pr 1981» has modified the classical KippenhahnSchluter solution to account for the vertically aligned fine structure of quiescent prominences. d. Mass flow and dynamic models. The dynamic nature of quiescent prominences are demonstrated by systematic and random motions measured in disk filaments (Martres et aI, SP~, )07. Malherbe et ~1' AA 102, 124). These authors find upward directed slow c,omponent (11::$ J km s ) in some filaments whereas Kubota (J-F S, 178) measures a predominantly downward flow in 2 of 3 filaments. Co-ronal cavities are slightly. deprived of matter as compared to the 'normal' corona (Lantos and Reolt, SP 66, 375. Kundu et aI, AA 94, 72), but the difference is not by far enough to form prominences. The cavities are enclosed by arcades of hot (magnetic) loops (Serio et aI, SP ~, 65. Chapman, SP 71, 151), which will prevent efficient flow of mass from the corona to the filament/cavity. These reasons and the fact that the prominence SUb-structures are short lived as compared to several solar rotations for the 'seat of the

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prominence appearance', have led to investigations of dynamic models for quiescent prominences of the Pikel'ner type where matter is sucked up along the magnetic field lines from the subjacent chromosphere (cf Leroy, J-F S, 155). Uchida (J-F s, 169) assumes a quadrupole component in the photospheric magnetic field which yields a 'neutral sheat' above the central polarity reversal. He s6lves the hydrodynamic equations for matter which flows from the chromosphere, through the cavity region~ and condenses by radiative cooling as it approaches the neutral sheet region. Ribes and Unno (AA 21, 129) derives a hydrodynamic model of a filament using a simpler magnetic configuration. Priest and Smith (SP ~, 267) aSSume that the presumed downflow along the vertical structures is a cnsequence of a small scale interchange or a Rayleigh-Taylor instability inside the prominences (see also Dolginov and Ostryakov, SAL £i, 749). e. The prominence-corona transition zone. The P-C interface region is assessed by observations of ~UV emission lines and cm-wavelength radio amission. The radio disk filaments have slightly lower temperatures than the quiet Sun at corresponding frequencies (Kundu et aI, AA 62, 431). The temperature determination is apparently sensitive to the spatial resolution of the observing antenna (cf Rao and Kundu, AA 86, 373). Schmahl et al (SP 11, 311) caution against the strict forward interpretation of microwave observations of disk dilaments since they exhibit substantial diversity and variability. Emission measure analysis based on absolute calibriated ~uv line intensities (Schmahl and Orrall, ApJ L~, L41) confirmes the essential of earlier works. The P-C temperature gradient is less than determined for the Ch-C zone, which implies that the thermal flux is comparatively lower (M~ltradian et al, AA 79, 138). Moe et al (SP g, 319) derived P =0.05-0.1 dyn cm in the P~C interface, which is only slightly higher than tKe values reported by Mouradian et ala Turbulence in the P-C transition zone (Moe et al, SP 61, 319. Vial et al, SP 68, 187), which evidently originates in the prominence itself, is assumed (van Tend, SP i&, 29) to generate MHD waves which will heat coronal loops of the helmet structure (see Chapman, SP 71, 151). III. Active Prominences a. Loop prominences. Loop prominence system (LPS), are usually considered as a signature for energetic flares, in particular, proton events. Basically, two hypothesis are debated to account for the energy and mass of LPS. They either grow out of stationary hot coronal loops, the thermal instability is triggered somehow by a near by flare, or they are the results of reconnecting magnetic field lines which initially were torn open by an erupting filament. Observational evidences for the latter case are presented by Martin (SP ~, 165) and Schmahl (SID, 241). Malville and Schindler (SP 70, 115) proposed that the flare will lead to enhanced dissipation and heating of the foot-points of the loops, which results in evaporation of matter (cf Antiochos and Sturrock, ApJ 220, 1137) into the loops and, subsequently lead to condensation. The flare loops systems seen in H grow, evidently, out of hotter coronel loops (McCombi and Rust, SP g, 143; Chapman and Neupert, ApJ ~, 799; Svestka et aI, SID, 217). Hood and Priest (AA 77,2.33) pointed out than an increase in the gas pressure beyond a critical value of a stable coronal loop, by f inst streching or twisting the loop, will lead to thermal instability and subsequently a cool core. Krieger (SP ~, 107) investigated coronal loops brightened by flares and concluded that the observed decay times were 10 times longer than predicted from cooling by thermal conduction. The disagreement may be caused by an anomalous conductivity, or by additional heat sources (Habbal et aI, SP 64, 287; Ionson, ApJ 226, 650). Cooling of flare loops have been analysed numerically by Antiochos and Krall (ApJ m, 788) who noted that thermal conduction dominates in the early cooling phase whereas radiative cooling is more efficient in the later phase. Antiochos

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270) assumed that the instability grew from a thermal perturbation the loop and showed that the temperature dropped from coronal to chromospheric value in the course of 5-600 s. The entire loop gradually cooled and the matter streamed down both legs at freefall conditions. Malville and Schindler measured a pronounced enhancement in the line-of-sight velocity (rms) which evidently was associated with the destabilization of the loop system. They also found a torsional motion and oscillation of the whole loop with a period of 75 min, which presumably was sub-Alfvenic. A longer period (340 s) has been reported by Zhugzhda et al (SDB 7/98) in another event. LPS as well as hot coronal loops are well represented by the lines of force of a dipole (Wu et aI, SP J..Q, 137; Antiochos, ApJ lli, 270; Engvold et aI, SP~, 331). The apparent twist motion of the falling matter (Tsubaki, MSUNS ~, 89) is evidence for force-free configuration of the magnetic loop which may arise by motion of their foot pOints (Sakurai, PASJ 21, 209). (~5%)of

b. Eruptive prominences. Recent studies of the kinematics and thermodynamics of eruptive prominences are based on data from X-rays, EUV and the visible. The generally accepted picture is confirmed that eruption involves real mass motions and that the force acting on the matter is directed upwards and away from the associated center of activity, the accelerations decreasing with time (Waldmeier, AMES No 371; Pittini, AMES No 373; Vrsnak, HOB~, 17; Delone et aI, SDB 1/102). The trajectories of the ejected material delineates the unwinding and streching of the initially loop-like magnetic field structure (Bhatnagar, SID, 235; Kleczek, HOB~, 35). Two peculiar cases have been'noted by Bruzek (SID, 203) where ejected filament material stopped at a distant position and formed short lived filaments. Tandberg-Hanssen et al (sp 65, 357) found that the material of flare sprays originated from preexisting filaments. The majority of eruptive prominences have height-speed relation in the range between the fast sprays and the slowly ascending prominences (~vold, SID, 173). In fact, Slonim (SA L..§, 21) demonstrated that the ascending velOCity varies inversely with the square of the distance between the filament and the nearest center of activity, which implies that the dynamics of eruption is a function of the magnet~c field strength. Observational evidence for rapid heating of the erupting prominence material has been presented by Webb and Jackson (SP 73, 341). Kahler et al (BAS 11, 659) concluded from studies of X-ray and H~--observations that filaments disappear in place without being ejected from the region. Also Mouradian et al (J-F S, 195) pointed out that, although material motions are observed in Ho( , many cases of "disparition brusques" are likely to represent a modification in the ionization of the prominence material rather than a dramatic restructuration of the magnetic field. These authors also noted the reappearance of a filament first in high temperature lines (Mg X). Sifrio et al (SP 59, 65) found out that prominences associated with young « 4 rotations)or very old (::> 8 rotations) neutral lines are significantly less stable than the average of all filaments. Unstable filaments tend to have hot coronal arcade loops spanning the filaments channel (Schmahl et al, BAAS]£, 526). Moore and LaBonte, SID, 207) proposed that the destabilization of a filament, its successive eruption and associated flare, result from reconnection of strongly sheared supporting field. Slonim (SA L..§, 21) concluded that the filament eruption and its associated flares are generated by a common mechanism which involves a preliminary reorganization of the magnetic field due to emergence of new magnetic flux. Pneuman (SP 65, 369) showed that a moderate increase in the magnetic field strength beneath the coronal helmet streamer can easily propel the prominence and the overlying arcade outwards. The mechanism which percipitates ttb.e prominence eruptions are believed also to, produce coronal transients (Fisher et aI, ApJ 1246, L161). 70% of all coronal transients are associated with eruptive prominences (Munro et aI, SP .21, 201).

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c. Surges. The mechanical energy of surges dominates by order of magnitudes the radiative output from flares (Webb, SFW, 471), but they produce no detectable coronal heating or dynamic responce such as coronal transcients (Rust et al, SFW, 273). The trajectories of the ejected matter are generally found to be ballisticlike (of Schmahl, SP ~, 135), though more complex behaviour have been reported (Makhmudov, SDB 5/81) Xu et al, AAS 5, 44). Xu et al claim that the mechanical energy of surges comes from dissipation of magnetic energy of the loop structure. Their conclusion is at variance with the results of Zach and Bar (SP 73, 331) who found that an active surge producing region was stable and Showed no evidence of decreasing energy. Stoyanova (SDB 3/84) noticed peculiar wave motions in surges which she proposed might give rise to condensation of matter in the magnetic structure and thus lead to the surge formation. The impulsive surge events are now also accessed in the EUV (Hence et al, BAAS 12, 532; Woodgate, BAAS 12, 535). Schmahl (SP 69, 135) analysed EUV data ~om Skylab and conclude~that inferred pressure gradients along the surges would be able to drive material outwards at the observed speeds and distances. Noci (SID, 307) applied a steady state apprOximation in a siphon type model to observed 0 VI and Mg X emission in a surge and found evidence for transversal pressure gradients. The response of the solar atmosphere to a brief thermal pressure pulse were investigated numerically by Steinolfson et al (SP ~, 187) who solved the one-dimensional time dependent hydrodynamiC equations and thus succeeded convincingly in simulating surge events. A different approach was made by Carlqvist (SP~, 353) who proposed that surges were the consequences of local evacuation arising from current driven instabilities at the top of magnetic loops. This model seems less convincing in explaining typical behaviour of surges. 6. FLARES AND ENERGE".rIC PARTICLES (D. M. Rust) A. Activities The Solar Maximum Mission satellite (SP 65, 5) was launched in February, 1980 and made X-ray and UV flare images for nine months. Besides the SMM, satellites launched for solar activity research included the International Sun-Earth Explorer (USA), Prognoz-8 (USSR) and Astro-A (Japan). One-arcsec observations of flares became available from the Very Large Array (USA) and Westerbork (FRG) radio telescopes. Important publications included the proceedings of the Skylab Flare Workshop (Solar Flares (SF», and Solar System Plasma Physics (SSPp), and Solar Flare Magnetohydrodynamics (SFMHD). Major reviews of flare observations by Brown, Smith and Spicer and of flare theory by Spicer and Brown appeared in The Sun as a Star lSS). First results from the SMM experiments appeared in Ap J L244, Ll13. Flare researchers lost an outstanding colleague in the death of S.I. Syrovatskii. A reView, "Key problems of flare theory" (IANSSR 43, 695) was among his last works. B. Research I. Flare Build-Up a. Preflare magnetic fields. New observational stUdies of preflare fields were few, but theoretical work intensified on analytic solutions to the forcefree field equation (Low, RGSP in press). Priest and Milne (SP~, 315) studied the evolution of arcade-like fields through a series of force-free ~tates, finding a solution that contains a magnetic bubble. They proposed that such a bubble could undergo an eruptive instability and trigger a two-ribbon flare. Hasan (SP 67, 267) found that any force-free field with constant twist is unstable-to kinking unless linked with a small, positive

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transverse gas-pressure gradient. Hood and Priest (SP~, 303 and SP~, 113) suggested that an MHD kink instability can develop into a flare in magnetic loops twisted through several rotations by photospheric motions. The dominant stabilizing effect which allows the accumulation· of energy in twisted fields is "line tying", i.e., the assumption that coronal field-line footpoints are fixed to specific photospheric sources. Gibons and Spicer (SP~, 57) criticized this assumption, which is fundamental to almost all work on magnetic energy build-up. b. preflare emission and activation. Observations of preflare conditions in the chromosphere and corona were reviewed by Martin (SP.§g, 217). She found that filament eruptions and X-ray brightenings, inter alia, were reliable flare precursors, but Mosher and Acton (SP~, 105) and Kahler (SP 62, 347) found no peculiar soft X-ray enhancements or filament activations that would allow small flares to be anticipated. Nevertheless, large flares are almost invariably preceded by filament activation and eruption. Kuperus and Van Tend (SP 71, 125) showed that if the background field near a filament evolves from a potential to a nearly force-free state, large forces are generated along the axis of the filament, if their earlier model (SP~, 115) is correct. They identify the filament eruption as the flare trigger. Most flare energy would be released as the magnetic fields reconnect after the eruption. II. Flare Energy Release Processes a. Magnetic field reconnection. Observations of H-alpha and EUV flare structures (Ap J Llii, L133; Ap J L244, L179) and of the underlying magnetic fields and X-ray flare kernels (ApJ L246, L155) continue to indicate that some flares, are triggered by emerging flux. Presumably, magnetic reconnection takes place at current sheets between the emergent and ambient fields. Alternatively, reconnection may occur in small segments within a twisted loop, (Spicer, SP lQ, 149). There would be no extended current sheet in this case. Mercier and Heyvaerts (SP 68, 151) reexamined the dynamics of the Petschek.-type extended current sheet. They find that plasma microturbulence, which many suppose to be the primary triggering mechanism of flares, does not appear in a straightforward way. They conclude that global properties of the active region magnetic structure as well as gravity may play an important role in determining current sheet dimensions and its effectiveness as a flare trigger. Syrovatskii and Kuznetsov (RPS, 445) and Smith and Spicer (SP 62, 359) pointed out that current sheets may be detectable with high resolution microwave observations. b. Double layers. Akasofu (SP 64, 333) revived interest in analogies between solar flares and magnetosphericsubstorms. The recent discovery of "double layers" above the ionosphere encourages the comparison. Double layers are narrow regions just above auroral arcs where the electric field is parallel to the magnetic field. In two-ribbon flares, Akasofu argued, the electron-accelerating layers could lie in the low corona near where the active region loop arcade intersects ,the chromosphere. The idea is a variation of the Alfven and Carlqvist model(Spicer, SP 70. 149); Carlqvist (SP 63. 353). c. Models -thermal and non-thermal. A burning issue in flare physics is the electron velocity distribution in the primary flare plasma. Current-sheet models lead to energization by joule heating (thermal model). However, accelerated electron beams (non-thermal model) are usually invoked to explain impulsive-phase X-ray bursts. In the thermal interpretation, (Smith agd Lilliequist, Ap J m, 582) ,hard X-rays originate in a very hot (1\110 K) plasma, while in the non-thermal interpretation, they are the bremsstrahlung emitted by electron beams interacting with a cold, dense plasma ("thick target"). The non-thermal interpretation of hard X-ray bursts requires about twenty times the energy in impulsive phase electrons as the thermal inter-

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pretation (Smith, SP 1&, 135). Unfortunately, X-ray spectra may be interpreted with equal facility either as the superposition of several Maxwellian or power-law flux distributions. Brown et al (SP~. 143) concluded that a single thermal source cannot describe the time development of hard X-ray spectra. They proposed that primary energy release sites consist of several small. impulSively-heated kernels, each cooled by anomalous conduction. Their model is an elaboration of de Jager's (SP 64, 135) view the impulsive-phase emission is composed of elementary flare bursts (EFBs). Evidence for EFBs is given by Karpen et al (Ap J £li. 370). Brown et al show how EFBs, which may correspond to sites of tearing-mode magnetic field dissipation (Spicer, SP 22, 305; SP lQ, 149; Van Hoven, Ap J ~; 572), may be revealed in dynamic hard X-ray spectra. Emslie (Ap J 244, 653) offered an alternative interpretation in terms of a single adiabatically heated region (Wiehl and Matzler, AA 82, 93) compressed by a time-varying, toroidal magnetic field. Kosugi (SP 71: 91) presented evidence for EFBs of N 3 s duration in an event with coincident bursts in hard X-ray, metric and microwave spectra. Radio interferometric observations suggested that the electron acceleration region (site of several EFBs) shifts in position after several tens of seconds. An important advance in understanding impulsive phase energy release came with the successful operation of the HXIS (Hard X-ray Imaging Spectrometer, SP i2, 39) on the SMM satellite. Hoyng et al (Ap J L246, L155) and Duijveman et al (SP, in press) showed that 16 - )0 keV X-rays integrated over 20 - 30 s spike bursts originated at the feet of magnetic loops (one loop for each spike burst). The loop feet lay above with H-alpha flare kernels. Hoyng et al believe their data show the bremsstrahlung of electrons accelerated non-thermally within the loops. Only the first few spike bursts in each HXIS event can be described in this manner. Most of the hard X-ray emission was in a hot, diffuse source that appeared after the first minute or so and coincided with the well-known soft X-ray and H-alpha flare loops. The first X-ray imaging results, then, seem to support both thermal and non-thermal models. The extreme energy requirements of the non-thermal model are avoided because non-thermal processes dominate for only a small fraction of the total X-ray burst interval. Marsh et al (Ap J 242, 352; Ap J L240, Llll), Kundu et al (Ap J 1981 in press) and Lang et al (Ap J 247, 338) reported microwave emission from 1-2" sources between H-alpha flare-kernels. In many cases, the microwave sources exhibited a double polarized structure. The circular polarization implied that the source was gyrosynchrotron emission from ~ 500 keV (non-thermal) electrons in 400 - 800 G magnetic loops. Although observations seem to favour non-thermal models, at least at flare onset, proposed acceleration mechanisms have raised many theoretical objections (Smith, SP 66, 135). The question of whether a thermal model with a high-energy tair-in the electron velocity distribution (Vlahos and Papadopoulos, Ap J 717; Emslie and Vlahos, Ap J 242, 159) can describe the observations will be studied intensively as mo're VLA and SMM results become available.

m.

d. Ion acceleration. Measurements of solar protons and other ions at 1 AU are only just beginning to reveal the properties of the acceleration region. Ion charge state measurements from the ISEE-3 and IMP-8 sp~cecraft indigate that flare particles are accelerated from plasma at 4 x 10 K to 5 x l07K 8 (Ma Sung et al, Ap J ~245, 45; Paris Cosmic Ray Conf., 1981), not in 10 _10 K kernels and not in 10 K ejecta. The results is exciting evidence for acceleration in ambient coronal material by shocks (Gutschenko and Zaitsev, SP jJ, 337). Acceleration of electrons by shocks certainly produces type II metric bursts, but since accelerated ions emit only negligible EM radiation, their association with shocks has_been much more difficult to establish. Furthermore, ion acceleration by the claSSical Fermi mechanism requires pre-acceleration, presumably during the impulsive phase. It appears that

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the shock drift acceleration mechanism (Pesses et al, SSR, in press; Decker, JGR~, 4537), in which shocks can rapidly accelerate ambient ions, may be operating in the corona as well as in interplanetary space, where it is well established. Curious data on elemental composition in solar particle events continues to stream in. Briggs et al (Ap J 1228, 183) found a strong tendency for second flares to produce H/He-enhanced energetic particle fluxes when compared with first flares from the same active region. Flares separated by > 100 h do not show the effect, which implies that flares may interrupt a gradual He enrichment process in active regions. MDbi~s et al (Ap J 238, 768) found that heavyion-rich events are also enriched in He and Fe. They vie~ this as due, not to gradual enrichment, but to preferential injection of He and Fe by turbulent ion heating and Fermi acceleration. On the other hand, Cook et al (Ap J 1238, 97) found that the average energetic particle abundances in four major flare events were similar to sOljr wind abundances. Small flare particle events, however, consistently show He and heavy ion enrichments (Mason et al, Ap J 1070). Kahler (JGR, in press) showed that earlier statistical stUdies linking impulsive phase phenomena to proton events did not adequately account for the fact that all flare phenomena are bigger and more frequent in major flares. After this "big flare syndrome" is accounted for, no significant correlation remains between proton events and impulsive-phase phenomena except for the time-integrated microwave burst energy. A popular two-step model, in which ion acceleration starts with injection during the impulsive phase, was challenged by first results from the SMM gamma-ray experiment (Forrest et al, SP 65,15; Chupp et al, Ap J L244, 1171; Ryan et al, Eos ~, 380A). Gamma-ray-emission from nuclei excited by 1 - 50 MeV ions appeared in ~ 1 s coincidence with impulsive-phase emissions from electrons and repeated quasi-periodically for ~ 40 s. The gamma-ray data clearly show that protons can be accelerated up to ~50 MeV in the impulsive phase. Few of these protons escape the Sun. Decker et al (Paris Cosmic Ray Conf., 1981) and Chambon (SP~, 147) found that gamma-ray events produce relatively weak proton events at Earth. We may have learned how to accelerate protons in shocks (Decker, loc cit), but we must now search for a way to accelerate them quaSi-periodically in the impulsive phase and on time scales that may be too short (Nl s) for shocks or wave turbulence (Barbosa, Ap J ~, 383) to operate.

m,

III. Flare Effects in the Solar Atmosphere a. Photosphere. The problem of whether white-light flares are the result of proton bombardment benefitted from several simultaneous gamma-ray and white-light flare observations (DezsD et al, SP 67, 317; Hudson, Ap J 1236, 91; Zirin and Neidig, Ap J L248, 45). Hudson and:Dwivedi (SP, in press;-analyzed the effects on the photosphere of high-energy ions capable of producing the July 11, 1978, white-light flare and found that photospheric heating by the ions would be negligible and that the emergent spectrum would be red rather than blue as observed. In the July 1, 1980, white-light flares, there was a correlation between gamma-ray and the white-light emissions only in the weakest phase of the white-light event. The brightest emission cannot be due to proton bombardment (Rust et al, SP in press). b. Chromosphere. Models of the effects on the chromosphere of different modes of energy input have improved substantially and left us with some difficult puzzles. Machado et al (Ap J 242, 336) devised semi-empirical flare model atmospheres that apprOximately reproduce observations in H I, Si I C I, Ca II and Mg II. Pure particle heating models cannot produce the observed emiSSion, and Machado et al suggest that conduction and X-ray photon heating (Henoux and Nakagawa, AA~, 385; Henoux and Rust, AA 91, 322) make substantial contributions in the lower chromosphere. No detailed energy input

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models have yet explained temperature minimum region heating (Emslie and Machado, SP 64, 129). Somov e~al (SP 73, 145) studied the hydrodynamic response of the chromosphere to electron beam heating. The top of the chromosphere to electron beam heating. The top of the chromosphere explodes into the corona at < 1500 km/s. In denser layers, the energy can be radiated away, and a UV flash results. High-resolution simul~aneous maps of hard X-ray and UV emissions showed that individual X-ray spikes can be identified with discrete UV flare kernels (Cheng et al, AP iT L248, L39). Several 4" kernels brightened sequentially in one studied flare. In a limb f~are studied by Pola~d et al (SP, in press), UV lines of 0 IV (T ""2.5 x 10 K) and Fe XXI (""10 K) showed that impulsive phenomena began in ~he chromosphere or photosphere and continued for several minutes as material was ejected into coronal loops. Nagai (SP 68, 351) studied gas-dynamic models of flare loops heated by thermal conduction from the top or foot. Cargill and Priest (preprint) studied loops heated by slow MHD shocks initiated by magnetic reconnection, as in Pneuman's model (Solar Flare Magnetohydrodynamics, Gordon and Breach). So far, none of the models is realistic enough for detailed comparison with observations. Somov's model (SP]2, 145) predicts that the ion temperature in the impulsive phase ejects will be an order of magnitude less than the electron temperature. It willbe difficult to check this prediction since impulsive-phase turbulence broadens the lines and mimics a high ionization temperature (Culhane et al, ApJ L244, L141). c. Corona. There is accumulating evidence for distinguishing two classes of least with respect 4to coronal manifestations. Small volume (10 -10 em), low altitude « 10 km) fla2'es ~ve shor!3rise and decay times and a high coronal energy density (10 -10 ergs cm). A compact flare that produced an extraordinary burst of hard X-rays and gamma-rays was studied by Dennis et al (Ap J L244, L167) and Ryan et al (Ap J L244, L175). Compact flares are not associated with coronal transcients, but lo~­ -decay (Nhours) e~Bnts26LD~'S), which have larger coronal loops (N 5xlO ~), larger v~lumes (10 -10 cm) and lower coronal energy densities (10 - 10 ergs cm- ) are associated with prominence eruptions and with coronal transcients (Pallavicini et al, Ap J ~, 108; Pallavicini and Vaiana, SP 67, 127). Krall et al (Sp 66, 371) made a one dimensional hydrodynamiC model of an LDE. In agreement withother studies (Moore et al,Solar Flares; p. 341; MacCombie and Rust, SP 61, 69), they found that energy is supplied to LDE's for hours after event onset. Clearly, energy release processes both rapid (e.g. Duijveman et al, Ap J 245, 721) and slow (Pneuman, loc Cit.) occur in a variety of flares and no single model or mechanism will describe them all. sol~6 fl~7es'3at

7. RADIO PHYSICS (M.Pick) Reviews and General A detailed review on Solar Radioastronomy has been published in book form by KrUger (ISRAR). It present!'! a summary of the work done during the past thirty years and covers instrumental aspects, observations and theory. In the book on the Symposium IAU No 86 (RPS), dedicated to the memory of S .F. Smerd, the present level of our understanding of Solar Radio Physics is summarized. Many books have included several aspects of the radio emission: PSP, IAU Colloquium No 44, the monographs from Skylab solar workshops, in particular: SF and CHHSWS. In order to detect the presence of expected Langmuir waves, microwave radar observations of the Sun have been made. The possibility of recognizing neutral current sheets in the corona by

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their radio emission has been discussed (Zheleznyakov and Zlotnik, SP 68, 317; Kurnetsov and Syrovatskii, SP~, 361; Nefed'ev, PAZ 2, 96). Quiet Sun Fluctuations of the radiflux have been studied at 2.8 cm (Butz et al, AA 72,211; Graf et al, ApJ 228,312). Radio pulsations with a period of 160 min were detected at 1.9-3.5 cm (Er,yushev et al, PAZ 2, 546). At decameter wavelengths, periods from 4 to 30 min were detected (Abranin et al, PAZ 4, 559). The radio granulation was observed with the RATAN-600 radiotelescope (Bagod, SSAOZ 12, 22). A map of the supergranulation network was obtained with the WSRT (Kundu et al, ApJ 234, 1122). Brightness distribution was studied at 2.4 cm (Borovik, PAZ~, 426). There is no change with the phase of the cycle (Borovik, AIISAOZ 11, 107). The variation of solar brightness at the extreme solar limb was observed at centimetre wavelengths (Lantos et al, SP ~,271). Synoptic charts of co' than F8-G5 stars with the same rotation rate. Vaiana et ale ( 1981, Ap. J., 245, 163 ) find that the surface flux fx of K and M dwarfs increases steadily with advancing spectral type, even though the angular velocity decreases with advancing spectral type along the lower main sequence ( Vaughan, A. H. et al., 1981, Ap. J. in press ). This suggests a strong increase of surface magnetic activity with increasing depth of convection zone (see eg, Linsky, J., 1981, in "Solar Phenom in Stars and Stellar Systems"). Such an increase finds a possible explanation in terms of dynamo theories of the generation and surface eruption of magnetic fields ( Durney and Robinson 1981, Ap. J. in press; Rosner and Vaiana 1981 ). (D) ACTIVITY CYCLES AND THEIR DEPENDENCE ON ROTATION AND CONVECTION ZONE DEPTH Vaughan ( 28 114 108 ) noted that of the stars monitored for activity cycles by Wilson ( 22 114 053 ), those with smoothly varying "solar-like" cycles lay below the Vaughan-Preston gap in stellar Ca II emission level, while stars above the gap showed large irregular fluctuations, without clear signs of periodicity. Vaughan et al.( 1981, Ap. J. (November) ) extended this to note that clear cycles appeared only for stars with rotation period exceeding about 20

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days ; all such stars lie below the gap. Aside from this result, no apparent relation was found between cycle period and either rotation period or convection zone depth ( ie, spectral type ). Belvedere, Paterno, and Stix ( 28065 060 ) carried out ~-~ dynamo calculations for lower main sequence stars, and predict an increase in activity cycle period toward later spectral types, which is especially sharp in the range F5 to KO. This is at odds with the observations mentioned above ; clearly such observations can provide new and useful constraints to dynamo theories. (E)

THEORETICAL IMPLICATIONS OF THE VAUGHAN-PRESTON 'GAP' If the Vaughan-Preston gap is a true physical effect, it strongly suggests two different modes of magnetic field generation, depending principally on stellar rotation rate. Durney et ale ( 1981, P.A.S.P. in press) interpret the gap as reflecting a higher mode of the ~- w dynamo for stars whose "dynamo number" Knobloch ( proportional to stellar rotation rate ) exceeds a critical value. et ale ( 1981, M.N.R.A.S. in press) on the other hand, argue that above a critical rotation rate convection tends to occur in rolls aligned parallel to the axis of rotation, leading to large toroidal fields but no helicity to recreate poloidal fields and produce a cyclical activity variation. Gilman (1981) reports non-linear dynamo calculations in which two classes of solution are found -one in which strong magnetic fields suppress the differential rotation and lead to strong, non-reversing surface fields, and one in which weaker fields allow differential rotation to perSist, creating the normal reversing dynamo. The explicit role of rotation in determining which class of solution prevails has not been calculated. (F)

IMPLICATIONS FOR THE EVOLUTION OF SOLAR MAGNETIC ACTIVITY It has sometimes been suggested ( eg, Blanco, et ale 1974, A.and Ap. 33, 257 ; Smith, M. A., 1979, P.A.S.A., 91,737 ) that the Sun has anomalously low Ca II activity and rotation rate for its age. However, Soderblom ( 1982, Ap. J. Sup pl., in press ) finds that the rotation rate of the Sun is only about standard deviation below the mean observed rotation rate for similar stars, so there may be no strong evidence that the Sun is Significantly anomalous compared to other lower-main sequence stars. If the Sun is typical, implications of the above results for its earlier history are ( Noyes, R. W., 1982, in "Physics of the Sun" National Academy of Sci. ) ; when the Sun was a younger star ( age less than about (1 - 2) x 10'1 years ) it had a rapid rotation rate (period less than about 10 days ), high levels of surface magnetic activity, and pronounced chromosperic and coronal emission ( eg, X-ray emission perhaps 20 times the present value). The solar activity cycle was either absent or, if present, was heavily masked by large irregular outbursts of activity. When its rotation decreased (through solar wind torques ) to a period longer than about 10 days, its field-production rate dropped rapidly to a lower level, presumably because of a change in character of its dynamo. Activity levels dropped, and at some later time its quasi-periodic activity cycle emerged as a dominant characteristic of its overall magnetic variability.

V. PHOTOSPHERIC MAGNETIC CONCENTRATIONS AND RELATED PROBLEMS ( H. C. Spruit ) Reviews related to this topic may be found in Livingston and Stenflo Reports on Astronomy Vol XVlla ), Cram ( 26 075 009 ), Schmidt ( 26 075 010 ), Spruit ( in "The Sun as a Star" ed S. Jordan, NASA SP-450 ). New Observation A line ratio method using 3 lines has been used by Wiehr ( 22 080 016)

to

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measure the intrinsic field strengths in plages and pores. The field strenghths found agree with those found by previous authors. Tarbell (22 072 063 ) developed a method to deduce intrinsic line profiles from unresolved measurements. He . finds field strengths around 1300 G, a reduced equivalent width, and the downdraft velocities of 0.6 - 0.9 km/s The profiles indicate that the downdraft velocity and the field strength are positively correlated in the magnetic elements, in agreement with finding by Frazier and Stenflo (22 072 041). Livingston found that field stengths of elements in quiet areas are significantly lower than in active areas field strengths below 1000 G do occur. Tarbell, Title and Schoolman (25 075 010) obtained magnetograms at very high spatial resolution (0.5"). They confirm the existence of high field strengths. An upper limit of 50 G was placed on the strength of a possible weak-field component such as the 'inner network fields' observed at Kitt Peak. Semel ( Astron. Astrophys. 97, 75 ) found a correlation between. the apparent ( unresolved) field strength and the equivalent width of the line. Vertical oscillations within the magnetic field were found by Giovanelli, Livingston and Harvey (22 080 047 ), at periods of about 5 min. They behave like the 5 min oscillation of nonmagnetic areas and are usually but not always in phase with it. Since only coherent motion in many magnetic elements is detected in this method, the oscillation seen is almost certainly due to driving by the ordinary 5 min oscillation of the photosphere. An interpretation in terms of the oscillation properties of an individual tube has, however, been given by Roberts. Magnetograms taken in chromo spheric lines have been used by Giovanelli ( 28 075 024 ) to explore the magnetic structure in the height range where the fields of individual flux tubes flare out and merge with each other. A method to interpret these magnetograms quantitatively was developed by Jones and Giovanell i ( Sol. Phys. 1981 ). Giovanelli finds from these data that the interface between the magnetic field and the underlying nonmagnetic atmosphere lies at a rather low height, about 400 km. This would not be compatible with existing models of this interface like those by Gabriel ( 18 073 076 ), which require heights of 1000-1500 km. High resolution pictures of faculae taken in the continuum at 470, 310, 210 and 200 nm were used by Herse ( 26 071 004 ) to derive the center-to-limb variation of the intensity contrast and the number density of facular points. The number denstiy decreases strongly towards the limb. Lifetimes and time scales of intensity fluctuations were determined by Hirayama (22 072 009 ) and by Komle ( 26 075 018), with similar results. Komle found also from magnetic Since measurements an rms inclination with respect to the vertical of 20· the buoyancy of a magnetic flux tube is very strong ( 25 075 016 ), this cannot be a steady inclination of the tube, and more likely it represents a swaying Measurements of the continuum contrast near the limb by motion of the tube. Klabunde ( thesis, 1981, Cal. State Univ., Northridge) indicate an increasing contrast down to at least cos &= 0.05. Interpretation, Flux Tube Models Interpretations of contrasts in terms of plane parallel or 'hot cloud' models were given ( 26 071 004 ; 22 072 009). Usually however it is realized that such interpretations give widely different results depending on the type of data used. This is due to at least two complicating factors. First, the temperature structure is probably strongly dependent on the size of the magnetic Secondly geomeelement ( 21 072 010 ; Spruit and Zwaan, Sol. Phys 70, 207). trical effects are quite strong for structures of the observed sizes ( 200 km or less). Two-component models based on line profiles taken at the disk center are relatively unaffected by the geometrical complications. Such models were given by Chapman ( 26 072 006 ) and Koutchmy and Stellmacher ( 21 071 039 ). They can be seen as approximations to the physical situation in a magnetostatic

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flux tube. In the photospheric layers the interior of such a tube is predicted to be cool with respect to its surroundings for all sizes, though due to optical depth effects it will appear dark only for sizes greater than about 0~8 ( 18 071 100 ; 20 080 072). This agrees with continuum observations at disk center ( Spruit and Zwaan, Sol. Phys. 70 207 ; Foukal, Duvall and Gillespie, 1981 ). At greater heights (the temperature minimum and higher) some The continuum form of heating is needed to explain the line contrasts. contrasts near the limb can be explained satisfactorily with Spruit's ( 18 071 100 ) 'bright wall' effect, down to cos 6- = 0 • 1. The high contrast at the extreme limb ( cos ~ = 0.05) seen by Klabunde ( see above) and Chapman may possibly be due to the real heating in the layers around the temperature m~n~­ mum. Continuum contrasts due to a hot flux tube wall were studied by Caccin and Severino ( 26 072 005). The effects of two-dimensional radiative transfer in the wing of Ca K, in narrow structures like flux tubes was studied by Owocki and Auer. They find that lateral escape of photons is important, but that it has very little effect on spatially averaged line profiles. Magnetohydrodynamics of Flux Tubes The theory of magnetic flux tubes has undergone a healthy growth. We will make a distinction here between 'thin tube' theory which is based on an approximation in which variations in physical quantities across the tube are neglected, and cases where this assumption is not made, but where the effects of gravity are neglected instead. In the latter, tubes of arbitrary diameter can be studied. We discuss these first. Wilson ( 25 062 001 ; 27 062 136 ; 27 062 095), Wentzel ( 25 062 069 ; 25 106 001), and Roberts (1981) and Edwin and Roberts (1981) studied the wave modes of magnetic interfaces of flux tubes. The modes can have the character of surface wav~s or body waves. Wentzel ( 25 062 069 ) interprets the rapidly propagating wave motions seen in Ha fibrils as surface waves. The behavior of thin flux tubes can be studied in an arbitrary stratified gravitating fluid. A general equation of motion for such flux tubes was derived by Spruit (Astron. Astrophys., 98, 155). The tubes have three modes of motion, which are analogous to the modes of an elastic wire under tension ( Spruit, Sol. Phys., Vol 75). One is an Alfven wave which propagates twists along the tube. The other two modes involve fluid motions along and perpendicular to the tube. For a vertical tube there is a purely longitudinal mode and a purely transversal wave. The transversal wave in photospheric flux tubes may be important in transferring mechanical energy from the convection zone to the atmosphere ( Spruit, Astron. Astrophys., 98, 155). The longitudinal mode of a vertical flux tube has been studied extensively. Defouw ( 18 080 013), Roberts and Webb ( 21 080 013 ) and Webb and Roberts ( 26 080 036 ) studied the case when the mode behaves as a wave. The wave has a cutoff frequency below which it is evanescent. Rae and Roberts (1982) studied the response to a longitudinal pulse in the tube. A wavefront propagates at the 'tube speed', beyond which a standing oscillation at the cutoff frequency occurs. This is analogous to the response of an isothermal atmosphere to an acoustic pulse. If the stratification is sufficiently superadiabatic, it was shown by Webb and Roberts, Spruit and Zweibel, Unno and Ando, and Parker that the mode can become unstable (22 080 054 ; 25 075 020 ; 27 075 005 ; 21 071 011). In the Sun, flux tubes are unstable if their field strength at the surface is less than 1300 G. Such unstable flux tube are transformed by the instability either into a dispersed weak field or into a stronger flux tube of about 1800 G ( 25 062 055 ). In the studies mentioned thus far, only adiabatic motions in the flux tube were considered. If exchange of heat between the tube and its surroundings is taken into accounts, the wave modes will be damped ( 28 062 087 ; 28 062 088 ), and instability can be changed into an overs table oscillation ( 25 062 055 ). The strong downdrafts observed in photospheric flux tubes ( 21 080 046

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continue to pose a problem for flux tube theory. Giovanelli ( 20 071 033 ) has proposed inflow by diffusion of neutral atoms with respect to ions across the magnetic field. The effect appears to be too small, however, to explain the observed velocities. Since the downdraft measurements are not made on individual flux tubes but represent some ensemble average, it is possible that the downdraft is not a net mass flow but results from an intensity-velocity correlation in a fluctuating flow as shown by Spruit ( 25 062 055). The effects of a steady downflow in a flux tube were studied by Unno and Ribes ( 25 071 015 ). The downflow of fluid along field lines during the eruption of new flux has been calculated by Shibata ( Sol. Phys., 66, 61 ). An important connection between flux tubes and the origin of spicules was made by Hollweg et al (1981) and Hollweg (1982). Nonlinear numerical simulation of an Alfven wave generated by a pulse at the photosphere and propagating upward along an expanding tube gives results that look rather like a spicule. A quite similar result is obtained if instead of an Alfven wave an acoustic pulse ( corresponding to the longitidinal tube wave ) is allowed to propagate upward along an expanding rigid tube. Distribution of Flux Tube, Connections with the Dynamo The process of emergence of a flux tube from below and the subsequent motion of the foot points over the surface, under the action of a supergranular flow, was studied by Meyer et al ( 25 075 016). The effect of the buoyancy is very strong near the surface, making the tubes almost vertical in the photosphere. Small flux tubes are carried around by the flow, and are swept to the boundaries of the supergranule cell. Bigger ones resist the flow. Parker (1982) showed that around fixed flux tubes the convective flow will organize itself such that the tubes are at the cell boundaries. The aerodynamic forces acting on flux tubes moving through a fluid were studied by Parker ( 25 062 064 ; 25 062 077 ; 25 062 079). Neighboring flux tubes which moved together are pulled towards each other by these forces. The distribution of sizes of flux tubes in an active region was studied by Spruit and Zwaan ( Sol. Phys., 70, 207). A maximum in the surface area covered was found at a diameter of 0 ~ 8. The power spectrum of the surface distribution of magnetic fields was compared by Knobloch and Rosner ( Ap. J~ 247,300 ) and Knobloch ( Ap. J., 248, 1126 ) with theories of turbulent diffusion. They find that the turbulent motions must be three dimenSional, that the effective diffusivity is large, at least of the order of 1012cm/s The depth at which the motions occur which are responsible for the observed power spectrum is found to be 15,000 km or more. Knobloch ( Ap. J., 247, L93 ) used a Simple model for the nonlinear interaction between convection and a magnetic field to derive a theoretical power spectrum that compares well with observations. The relative frequency with which unipolar and mixed-polarity areas occur during the solar cycle has been given by Giovanelli (1982). Parker (1982) has studied the effects which the flux tube nature of a magnetic field may have on the operation of a turbulent dynamo and found no new effects. The speed of rise'of horizontal flux tubes due to buoyancy has been reinvestigated by Schussler ( 28 062 033 ) and Kuznetsov and Syrovatskii 26 075 019). These authros find rather low speeds, which allow the flux to be kept within the convection zone during the cycle. Acheson ( 25 062 087 ; 25 075 001 ; 25 075 021 ) and Spruit and Van Ballegooijen (1982) have studied the breakup of horizontal flux tubes by buoyant instability. This process will destroy the toroidal field on a short time scale unless the stabilizing effect of solar rotation is strong enough. The structure of magnetic flux tubes which have emerged from deep-lying horizontal tubes was investigated by Van Ballegooijen (1982). Piddington 1981, 1982 ) repeated his objections to the turbulent dynamo theory and stressed the importance of twists stored in the emerging flux for generating chromo spheric and coronal activity.

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VI. CORONAL LOOP STRUCTURE AND ITS HEATING MECHANISM ( E. R. Priest ) Coronal Loops The coronal magnetic configuration consists of open flux tubes containing out-flowing solar wind plasma and closed flux tubes ie, coronal loops containing plasma at a higher density and higher temperature. The closed regions are inhomogeneous, so that certain flux tubes tend to stand out, possibly because of an inherent filamentation of the coronal field or a variation in the footpoint pressures. Such coronal loops were studied extensively with the Skylab satellite ( 28 003 011 ; 28 076 019 ; 27 074 038 ; Orrall, F. Q. 1981 ; Webb, D. F.1981, both in "Skylab Active Region Workshop" ed Orrall ) and they may be classified into different types ( 22 074 005). Interconnecting loops joining different active regions have lengths 20-700 Mm ( 1M~= 10 6 m ), temperatures of about 2 x 10 6 K and densities of 7 x 10 14 m- 3 , while qUiet-region loops are cooler ( (1.5 - 2.1) x 10° K) and rarer ( ( 0.2 - 1.0) X 10 lS m- 3 ) and active-region loops ( in X-rays) are hotter ( (2.2 - 2.8) x 10 6 K ) and denser ( (0.5 - 5.0) x 10"m- 3 ). A subclass of active-region loops known as sunspot loops have as their footpoints sunspot umbrae and contain low-temperature ( 10 5 K ) cores. Flare loops may be divided into two classes, namely post-flare loops with L = 10 - 200 Mm, T~5 x 10' K, n < 10 1'7 m-3 and simple ( or compact) flare loops 5 - 50 Mm long with T < 4 X 10 7 K and n < 1018 m- 3 • The two main realizations of the past few years about coronal loop plasma are that it is dominated by the magnetic field and that it is extremely dynamic, showing continual activity with a wide range of flows, especially inside active region ( Athay, R. G., 1981 ; Priest, E. R., 1981 ; both in "Skylab Active Region Workshop" ) small-scale flows of 10 - 30 km/s are suggested by non thermal broadening, and ground-based instruments show continual surging, coronal rain and spicules, while space observations ( Athay, R. G., 1981 ; Brueckner, G. E., 1981 ; both in "Skylab Active Region Workshop" ) reveal small transient explosions and microsurges, as well as large-scale steady upflows over sunspots, up-and-down-flows over plages and downflows over the network and filaments. Coronal Loop Models As a preparation for the study of loop motions, much work has been expended First of all, an order-of-magnitude on setting up models for static loops. scaling law (T~( po L)Y3 ) for the summit temperature (T) in terms of the base pressure (p.) and loop length (L) was derived ( 21 074 007 ) by equating the radiation ('Xn'/T '/2. ) and conduction. The solutions for uniform pressure were considered in more detail by many authors ( 22 074 005 ; Monsignori-Fossi, B. C., 1981, in "Solar Activity" ed C. Jordan ; Withbroe, G. , 1981, in "Skylab Active Region Workshop" ), by seeking analytical (28 074 079) and numerical (26 074 016 ; 27 074 060 ) solutions, both thermally isolated and not thermally isolated ( 26 074 016). It was found that the scaling laws ( 28 074 079 ; 26 074 016 ; Monsignori-Fossi, B. C. , 1981, in "Solar Activity" ) and the emission measure ( 22 074 035 ) are not very sensitive to the detailed form of the heating function. In principle, it should be possible to deduce the form of the coronal heating from the observed lengths, pressures and temperatures of coronal loops, but in practice the observational errors are too large and the models too insensitive. For example ( Chiuderi, C.et al., 1981, Astron. Astrophys , 97, 27 ), with a heating proportional to T' , 10% observational errors imply a value of~ anywhere between -2 and 7. The above theory applies only for very low-lying loops. Its extension to loops in hydrostatic equilibrium and with non-uniform cross-section ( 26 074 020 ; Wragg, M. A. and Priest, E. R. , 1981, S,ol. Phys. 70, 293 ; Serio, S.' et al., 1981, Ap. 249, 288 ) shows how gravity lowers the pressure

+,

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and density substantially and the temperature slightly, while a reasonable divergence in loop area can easily change the summit temperature by a factor 2. The thermal stability of uniform-pressure loops depends crucially on the assumed boundary conditions ( 21 074 032 ; 26 074 007 ; 27 074 076 ), but the loops appear to be unstable if the base conductive flux is low enough. In particular, thermally isolated loops, whose base flux vanishes, are unstable, which may account for the presence of continual plasma motion in the transition region and corona. However, the inclusion of gravity stabilizes loops that are long enough ( Wragg, M. A. and Priest, E. R. 1982, submitted ). Two more extensions of the basic theory are to include steady siphon flows driven by a pressure difference between two footpoints ( 27 074 034 ; Noci, G., 1981, Sol. Phys., 73, 67 ; Glencross, W. M., 1981, Sol. Phys., 73, 67) and to model the thermal structure for a complete magnetic configuration ( rather than just a single field line). Two examples of the latter are a modelling of the transverse pressure structure in a loop together with the thermal structure along it ( 26 074 016 ) ; a solution for the thermal structure along each field line of a force-free coronal arcade ( 26 073 073 ). In future, one hopes to see more numerical simulations ( 25 073 083 ; 28 073 114 ; 28 074 095 ; 22 074 035 ; Craig, I., 1981, in "Solar Flare MHD" ed Priest ) of time-dependent flows in loops, with an adequate treatment of the transition region and of the coupling of the coronal part of a loop to its optically thick chromo spheric and photospheric base. Magnetic Heating The heat that is required to balance radiation and conduction in the corona is typically 300 Wm 2 in quiet-region loops and 5000 Wm 2 in active-region ones ( 20 073 050). It is now generally accepted on both observational ( 22 073 069 ; Mein, P. et aL, 1981, in "Japan-France Seminar on Sol. Phys" eds Moriyama and Semel ) and theoretical grounds that acoustic shocks do not heat the corona ( although they may be effective for the low chromosphere ( 26 064 006 ; Ulmschneider, P., 1981, in "Solar Pheom. in Stars and Stellar Systems" eds Bonnet and Dupree). In particular, the OS0-8 observations show an upward propagating five-minute wave train at the temperataure minium, but by the time the transition region is reached the fluctuations have become aperiodic and the energy flux has decreased to only 10 Wm- 2 • Presumably, this is because of scattering off spicular inhomogeneity and refraction away from the vertical. Thus, attention has been turned to some kind of magnetic mechanism ( Chiuderi, ~, 1981, in "Solar Phenom in Stars and Stellar Systems" ; Hollweg, J., 1981, in "Skylab Active Region Workship" ; Heyvaerts, J. and Schatzman, E., 1981, in "Proc. Japan-France Seminar on Sol. Phys~ ), as outlined below. (A) MAGNETOACOUSTIC WAVES The basic theory ( Osterbrock, D. E., 1961, Ap. J., 134, 347 ) for magnetic wave propagation, steepening and damping in a weak uniform field needs to be reinterpreted in the light of both the field concentration to kilogauss values at supergranulation boundaries and also the inhomogeneouS.nature of the coronal field. Fast modes in a coronal loop whose denSity is larger than that of the ambient medium tend to be guided along the loop, since they are refracted away A calculaton for 2s from the surrounding medium with its higher Alfven speed. waves of the ray paths and of collisionless damping where the plasma beta exceeds 0.1 shows that a loop shape is heated preferentially ( 26 074 053 ). More details of the damping of fast modes by collisionless, viscous and conductive dissipation have been presented by Zweibel ( 27 074 078 ). Difficulties with fast modes ( Hollweg, J., 1981, in "Skylab Active Region Workshop" ) are the chromosphepic damping of low-period waves, the reflection at the transition region and the fact that observed photospheric motions would produce vertically evanescent waves unless the horizontal wavelengths were large, which would require a non-local analysis.

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(B) ALFVEN WAVES For field strengths larger than 10G the problem is to explain how an Alfven wave can give up its energy, since the damping is so small and it doesn't steepen easily. One possibility is nonlinear interactions ( 11 074 052 ; 20 074 048 ) with another Alfven wave or a non-uniform field to produce acoustic waves which then steepen and dissipate rapidly. By this process, short-period (10s) Alfven waves may heat weak loops ( 10-20G ). Hollweg ( 26 080 007 ; Hollweg, J., 1981, Sol. Phys., 70, 25 ) points out that the dominant fluctuations in the solar wind at 1AU are observed to be Alfvenic, with periods of an hour or more. He models linear propagation near the axis of a vertical tube in a model atmosphere and suggests that in open regions waves with periods between 10s and 5min can heat the corona by ohmic dissipation or nonlinear coupling to magnetoacoustic modes. (However, a consideration ( 28 062 081 ) of wave reflection in a uniform vertical field shows that for a field of 1G ( or 3000G ) the period must be less than 1hr ( or 1s ) if the waves are not to be almost totally reflected at the transition region. Thus, only short-period Alfven waves can use intense tubes as ducts to reach the corona.) In closed regions, Hollweg points out that periods smaller than 10min are reflected back down at the transition region, except for resonant frequenceies at which a number of wavelengths fits along a loop and there are windows that allow a large flux to reach the corona. (C) SURFACE WAVES Along the boundary of a coronal loop, surface waves may propagate and provide heating ( 22 074 051 ; 25 062 069). They are quite distinct from the normal body waves and have profiles that decay exponentially with distance away from the boundary. The properties of such waves on an interface, a slab or a cylindrical flux tube are being investigated ( 27 062 136 ; Roberts, B., 1981, Sol. Phys., 69, 27; 69,39; Spruit, H. C., 1981, in "The Sun as a Star" ed S. Jordan; Spruit, H. C., 1981, in "Solar Phenom. in Stars and Stellar Systems" ). There are two main types, corresponding to slow and fast magnetoacoustic waves, but there is no equivalent to the normal shear Alven wave. Each type in a flux tube may be either kink-like or sausage-like in nature. When the finite thickness of the boundary is included in the analysis no steady, ideal surface modes exist, but the presence of dissipation should allow a steady solutioin, and an initial-value treatment reveals a build-up along the boundary of large motions which eventually dissipate viscously or ohmically ( Rae, I. and Roberts, B., 1981, Geophys. Astrophys. Fl. Dyn , in press). If the boundary is so thin that the fluid analysis fails, a surface disturbance may feed energy into a kinetic Alfven wave which dissipates by collisionless effects ( 22 074 051 ). This is a very lively topiC, and in future one can expect much progress in understanding the properties of surface waves. A related topic that is a prime candidate for coronal heating is the resonant absorption of waves at surfaces within a magnetic arcade where the wave frequency matches the local Alfvenic or cusp frequency. (D) DIRECT MAGNETIC DISSIPATION When the time-scale for photospheric motions exceeds the time ( L/VA ) for a disturbance to propagate along a loop ( of length L ), a wave description is no longer helpful. For example, this applies to a loop of length 100 Mm when~> 5 min. The problem then is how does the corona respond to such slow footpoint motions produced by, for example, mesogranula tion (-r; ~ hrs ) or supergranula tion (l, ~1 day )? It may evolve passively through a series of largely force-free equilibria, storing energy in the process ( Uchida, Y., 1981, in "Japan-France Seminar on Sol. Phys~). At the same time, the field may dissipate the energy either continuously or sporadically in current concentrations. In this picture of magnetic ( or current) dissispation the corona is in a state of ceaseless activity as it is being heated by microflarings ( 28 003 011 ; Priest, E. R.,

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1981, "Solar Flare MHD"). The actual means of dissipation is similar to that of a magnetic wave mechanism, since a region of high field gradient is formed In the previous and then the energy is released ohmically and viscously. mechanism a current sheet is propagating ( a shock wave ), but here it is non-propagating, and so the essential problem is how to form such a current sheet ( see (E) below). Order of magnitude estimates ( 10 074 109 ; 27 074 052 show that the upwards energy flux (VB 2. If-) in a field of 100G is sufficient to supply the corona when the photospheric motions are only 100 ms Also, in order for the energy to dissipate fast enough, the currents need to be concentrated into sheets, sheaths or filaments. It is unlikely that the sheets are strongly turbulent, since they would decay extremely quickly and the necessary current densities are immense. A more likely alternative is the formation of sheets by resistive instability ( Galeev, A., et al., 1981, Ap. J., 243, 301 ). Further, the energy increase by stochastic footpoint motions may be used to estimate scaling laws for loop temperature ( Sturrock, P. A., and Uchida, Y., 1981, Ap. J., 246, 331 ). (E) CURRENT CONCENTRATION The formation of current sheets has long been studied in connection with solar flares ( eg, Priest, E. R., 1981, in "Solar Flare MHD" ). One way to create such sheets is by the interaction of topologically separate parts of the field due to photospheric motions ( 22 062 010). Another way is through magnetic nonequilibrium when the corona cannot find a force-free equilibrium. A small photospheric displacement from one equilibrium does in general lead to another equilibrium ( Sakurai, T. and Levine, R., 1981, Ap. J. submitted ), but In a large displacement may produce topological dissipation ( 7 062 036 ). particular, a large movement of the feet of a flux tube within a coronal arcade may cause the tube to become dislocated from its neighbouring field, so that in its new position it is flattened and dissipated ----- "dislocation dissipation" ( Parker, E. N., 1981, Ap. J., 244, 631 ). Furthermore, it has been shown that a continuous deformation of a force-free field in general produces current sheets ( 22 062 009 ; 25 062 056). It is only for particularly Simple fields that such sheets do not arise. Current filaments may be produced by resistive instability due to the gravitational, rippling, and tearing modes, whose nonlinear evolution needs to be studied in a parameter regime relevent to the solar atmosphere ( Spicer, D., 1981, Sol. Phys., 70, 149 ; Van Hoven, G., 1981, in "Solar Flare MHD" ; Pellat, R., 1981, in "Solar Phenom. in Stars and Stellar Systems"). They can also be created by thermal instability ( 27 074 078 ; 12 062 062 ; 26 075 004 ), which causes a uniform current to concentrate into threads parallel to the magnetic field. The result is that the solar atmosphere is likely to have a filamentary character.

VII. CORONAL TRANSIENT ( E. Hildner ) Mass Ejections from the Solar Corona The brisk pace of coronal transient research has resulted in a better appreciation of both the observed properties of these events and a deeper understanding of the theoretical models which might describe them. As new observations from orbiting coronagraphs ( Naval Research Laboratory's SOLWIND and High Altitude Observatory's Coronagraph/Polarimeter ) and ground based instruments ( High Altitude Observatory's K-coronameter ) are just now appearing in the literature, we can expect coronal transient research to continue vigorously.

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Observed General Properties The associations between coronal transients and surface activity may give clues to the mechanisms responsible for the spectacular mass ejections. During the Skylab era, three-quarters of the ejections appeared to arise in or near active regions ; eruptive prominences, with or without flares, were apparently associated with 70 percent of coronal transients, the highest association of transients with any form of activity. Flares were associated with only 40 percent of transients ( 25 074 023). Examining the eruptives in more detail, Trottet and MacQueen ( 28 074 080 ) found a strong correlation between regions where the filament axis was north-south and the occurrence of transients with loop-like appearance. They deduced that most loop transients were nearly coplanar with the pre-event axis of the associated filament. As yet there is no consensus whether the coronal transients appearing as arches in images from orbiting coronagraphs are better characterized as "loops" or as "bubbles", that is, as relatively thin, two-dimensional objects or as phenomena having approximately as much depth along the line of sight as extent in the plane of the sky. Transients' forerunners, rims of enhanced density surrounding every Skylab transient for which adequate data were available, were found ( 22 074 073 ), indicating that a coronal disturbance starts not only higher but perhaps earlier than the surface activity with which a transient is associated ( Jackson, 1981, Sol. Phys., 73, 133). Support for the idea that the coronal transient disturbance begins before the surface activity is found in the observation that, statistically, type III bursts emanating from regions around the sites of coronal transients tend to occur more frequently some hours before the transient event than at any other time in the 48 hours centered on the event ( 28 077 028 ; 28 077 039). Fisher et ale ( 1981, Ap. J., 246, 161 ) have reported one transient which was present and moving at 1.2 R ,30 minutes before the associated eruptive prominence began to ascend. It remains to be seen whether this behavior is typical when viewing transients at heights below the limits set by the occulting disks of orbiting coronagraphs. Mass flowed up the legs - the only parts of the original loop still visible in the coronagraph field of view - of Skylab transients for several days after the passage of the transient front. This mass flow up the legs could account for up to 10 percent of the total excess mass delivered by the transient to the interplanetary medium ( 25 074 021 ). Radio observations may be used to determine the magnetic field strength in and/or around a transient and to help discriminate between models of transients. Gergely et ale ( 25 074 061 ; 28 074 060 ) find type IV radio emission to be cospacial with a secondary loop, far beneath the primary, outer loop in a Skylab event. Under the assumption that the emission is due to gyro synchrotron radiation, a magnetic field strength of a few gauss at 2.1 Ro may be inferred, leading to a value to about one for the ratio of gas pressure to magnetic energy density. With Dulk et ale ( 28 074 129 ), this implies that at least some transients are magnetically controlled. Similarly, Wagner et ale ( 1981, Ap. J., 244, L123 ) found that a moving type IV burst was cospacial with the leading white light loop of a transient observed with the SMM coronagraph. Maxwell and Dryer ( 1981, Sol. Phys., 73,313 ) suggest that the type II bursts due to shock waves should be well ahead of the white light transient loops, but this suggestion may not endure as SOL WIND and Coronagraph/Polarimeter find additional events. We note that the Jackson ( 1981, Sol. Phys., 73, 133 ) and Fisher et ale ( 1981, Ap. J., 246, L161 ) observations imply that if the type II shock starts low in the corona at the time of the flare or eruptive prominence, then it might find itself below and behind ( albeit at a higher speed ) than the broadband transient front. Observations of coronal transients near solar activity maximum are just now being reported. Fisher and colleagues ( 1981, Ap. J., 246, 1005 , 1981, Ap. J., 246, L161 ), using ground-based data, report the occurrence of dark transients, corresponding to density depletions, in the corona below 2 Ro. As

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a dark loop transient rises and expands, bright "horns" begin to form on each side of the dark area i with time the leading edge of the dark feature acquires a bright sheath which joins together the bright "horns" so that the dark transient depletion is surrounded by a bright transient density enhancement. By this time, the initially dark transient has brought new excess mass into the coronagraph field of view ( < 1.1 to > 2.0 R0 ). The new observations permit the characteristics of coronal transients observed above ~ 2 R~ during the declining phase of the solar cycle to be compared with similar characteristics for transients occurring near solar activity maximum, as observed from OS0-7 and Skylab. Near-maximum SOL WIND ( 27 074 064 i 27 074 044 i 28 074 047 i 1981, Sol. Phys., 69, 169 ) and Coronagraph/Polarimeter ( 1981, Ap. J., 244, L117 ) observations agree that transients in the two eras statistically had about the same speeds, masses, shapes, and surface activity associations. However, transients were seen at higher latitudes around activity maximum (28 074 044 i 27 074 044 i 27 074023 i 1981, Sol. Phys., 69,169 i 1981,.Ap. J., 244, L117) and more commonly than near activity minimum, H-alpha emitting material was seen rising to great heights in the interiors of Thomson scattering transients. Theoretical Models A number of workers haved analytically considered discrete structures which Van Tend might become coronal transients of "loop" rather than "bubble" form. ( 25 074 020 ) showed how destabilization might allow initial upward movement of an idealized loop carryhing current i this would set the stage for Anzer's ( 21 074 053 ) description of a transient proceeding outward as though it were an expanding current. Pneuman ( 27 073 044 ) showed that an increase of magnetic flux under a filament will drive it outward, in turn propelling the magnetic field and material originally residing in the helmet streamer presumed to lie over the pre-eruptive filament. This increase in flux below the filament may come about due to reconnection (28 074 063 i 28 080 039). Yeh and Dryer ( 1981, Ap. J., 245, 704 i 1981, Sol. Phys., 71, 141 ) have shown that pressure forces within transients must be considered when calculating the movement of the mass elements making up a transient. A possible way to probe the magnetic and density structure of a loop-shaped coronal transient using Faraday rotation of a linearly polarized signal transmitted to Earth from a satellite nearly behind the Sun has been given by Bird et al.( 28 074 070 ). Numerical, continuum models of coronal transients become increasingly sophisticated. In these models a pre-event corona is prescribed, a perturbation is introduced at the base of the corona, and the consequences of the perturbation are followed in time. In a,series of papers Wu, Nakagawa, and Han (21 062 004 21 074 002 i 1981, Ap. J., 244331 ) and ( 22062037 ) show that a pressure pulse in an initially hydrostatic, two-dimensional atmosphere will create a rising density enhancement which looks more like an observed transient if the magnetic field is "open" to interplanetary space than if the field is "closed" back to the solar surface. A similar calculation in non-planar, two-dimensional geometry suggests that rising material should spiral upward in open field configurations and stretch closed field lines in such a way as to reduce shear ( 28 074 071). Steinolfson, Wu, Dryer, and Tandberg-Hanssen ( 22 062 018 i 25 074 035 i 1981, Ap. J , 243, 641 ) considered similar problems with similar results. Substituting an ambient corona flowing outward to make the solar wind for earlier hydrostatic background corona seemed to make little qualitative difference in their results. In one case where material outflow was permitted, a coronal streamer took about 3 hours to reform after a simulated transient occurred dur to a pulse at the base of the streamer ( 28 075 021 ). More detailed descriptions of individual coronal transient events are available ( Fisher and Poland, 1981, Ap. J., 246, 1005 i Fisher et al., 1981, Ap. J., 246, L161 i Gergely and Kundu, 28 074 060 ; Gergely et al., 25 074 061 ; Michels

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et al., 28 074 067 ; Sheeley et al., 27 074 042 ; Wagner et al., 1981, Ap. J., 244, L123 ; Webb and Jackson, 1981, Sol. Phys., 73, 341 ), and reviews of the observations and theoretical models of coronal transients may be found also in Anzer ( 28 074 062 ), Dulk ( 27 074 063 ), MacQueen ( 1980, Phil. Trans. Roy. Soc. London A297,605), Rust et al.( 28 073 133 ), Stewart ( 28 074 065 ), and Wu ( 28 104 065 ).

VIII. CONCLUSION The above are brief descriptions of the advances in several sub-fields of solar phYSics which, among others, attracted attention in the past three years. For example, the close-up of solar type phenomena in other stars, the findings that the sun shows a light variation, although slight, and that the power spectrum of the global five-minute oscillation has very fine substructures suggesting the presence of a high-Q resonator inside the sun, are new aspects dealt with in this Commissioin report. The former two of these examples, like the investigations of coronal loops and coronal transients, have advanced through new space-oriented observations, but in comination with the ground-based observations accumulated over the last tens of years. The progress in the third example has been partly brought about by the introduction of a handy new technique, and having sought a suitable observing site available on the earth ( the South Pole). These examples show that while space platforms will play more and more essential roles in solar physics, long time-spun ground-based efforts with inventive experimental formulation can continue to play indispensable roles. We believe that the increasing accumulation of knowledge to be brought about by the integral efforts of observations, ranging from pilot experments to enduring routine observations, combined with the theoretical trials of consistent interpretations, will lead us to a deeper understanding of the sun, a representative of the stars which are the fundamental constituent of the universe. Finally I would like to express my deepest appreciation to the Vice-President and Members of the Organizing Committee for their valuable cooperation throughout the term. Yutaka Uchida PreSident, Commission 12.

CO~MISSION 14: ATOMIC AND MOLECULAR DATA (DONN~ES ATOMIQUES ET MOLECULAIRES)

PRESIDENT: J. G. Phillips VICE-PRESIDENT: A. H. Gabriel ORGANIZING COMMITTEE: D. R. Johnson, S. L. Mandel'shtam, R.W. Nicholls, S. Sahal, K. Takayanagi, E. Trefftz, W. Weise. General The rapid expansion during the past few years of the spectral region accessible to astronomical observers, from gamma rays to the radio region, has resulted in a corresponding expansion of the need for a wide variety of atomic and molecular data. Included are needs for accurate wavelengths, atomic and molecular energy levels, and transition probabilities. The continually improving resolution that has been attainable has resulted in the requirement of improved insight into line broadening mechanisms of various types. This expansion has placed an increasing premium on data compilation and dissemination, so that available information can be made readily available to potential users. Among the numerous compilations that have appeared might be mentioned the important ,National Bureau of Standards Bibliography on Atomic Levels and Spectra, which is up-dated periodically via successive supplements, and the NBS compilation and bibliography by the Data Center on Atomic Transition Probabilities. Several compilations or bibliographies on collision crosssections are now available, such as that published by the Information Center at JILA. In the field of molecular spectra there has appeared the very comprehensive "Constants of Diatomic Molecules" by Huber and Herzberg. Other useful compilations are referred to in the reports of the five Working Groups that appear below. WORKING GROUP 1:

WAVELENGTH STANDARDS The Primary Standard and the Rydberg

The present situation as regards the primary standard may be summarized as follows: the International Metre is officially based on the 606 nm wavelength of 86Kr, reproducible to about 2x10-9 • More reproducible wavelengths emitted by lasers stabilized on lines of 12, CH4 and C02 are known to about the same uncertainty and can be considered equivalent to the primary standard. The frequencies of the CH4 and some of the C02 lines are known in terms of the Cs primary standard of frequency to better than 10-9 • The resulting calculated value for the speed of light (c = 299792458 m s-l) has been adopted as the best value by the International Committee of Weights and Measures, with the recommendation that in any future redefinition of the metre, or of the second, this value should be unchanged and should be considered as exact. This is equivalent to an unofficial definition of the metre in terms of the speed of light and the second. In all probability such a definition will be formally adopted by the General Conference of Weights and Measures in 1983 but this depends on agreement on such matters as wording, adequacy of data and suitability of practical comparison techniques to ensure that the redefinition will provide a new more precise and widely reproducible standard, without significant discontinuity in the value of the metre. These questions will be considered during 1982 at meetings of the International Committee of Weights and Measures and its appropriate advisory committees: it now appears likely that the new definition will be in terms of the distance light travels in 1/299792458 seconds. New measurements of the Rydberg have been made by Lichten et a1. (1) in the U.S. and Petley et al. (2) in Britain yielding 109 73731.521 (11) m- 1 and 109 737 115

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31.513 (85) m- 1 respectively, in good agreement with one another but significantly higher than that of Hansch et ale reported in 1978. References 1.

Amin, S.R., Caldwell, C.D., and Lichten, W.: 1981, 2nd IntI. Conf. on Precision Measurement and Fundamental Constants, June 9, Gaithersburg, MD. Will appear as a special NBS publication in 1982.

2.

Petley, B.W., Morris, K., and Shawyer, R.E.: 1980, J. Phys. B: Atom Molec. Phys. 13, p. 3099. K.M. Baird Chairman of the Committee

WORKING GROUP 2:

ATOMIC TRANSITION PROBABILITIES

The Data Center on Atomic Transition Probabilities at the National Bureau of Standards, Washington, D.C., has continued its critical compilation and bibliographical work on transition probabilities. An extensive critical compilation (262 pages) has been completed for the three elements Fe, Co, and Ni (1), which covers all stages of ionization on which reliable data are available. Also, a table of transition probabilities for about 5000 selected lines of all elements for which reliable data were available on an absolute scale was recently published (2). Work is now in progress on the updating and revision of the existing NBS critical data compilations for all allowed (1,3,4) and forbidden (5) transitions in Fe-group elements. A single volume containing all these data for the Fe-group elements Sc to Ni (Vol. III of the NBS series of atomic transition probabilities) is planned for publication in the 1982-1983 period. A new supplemental bibliography has been published, covering the literature references from November 1977 through March 1980 (6). It contains approximately 600 references in chronological order and includes listings by element, stage of ionization, and experimental or theoretical method applied, as well as an author index. Below, the most recent literature references covering the period since the publication of our last supplement (March 1980) up to the present (August 1981) are listed (refs. 7-198), ordered alphabetically according to authors. Each reference contains some code letter(s), indicating the method(s) applied by the author. Specifically, the code letters are defined as follows: THEORETICAL METHODS:

Q - quantum mechanical (including self-consistent field) calculations.

I - interpolation within isoelectronic sequences, spectral series, or homologous atoms; also, data that are presented in graphical, rather than tabular form.

EXPERIMENTAL METHODS: E - measurements in emission (arc, furnace, discharge tube, shock tube, etc.). A - measurements in absorption (King furnace, absorption tube, etc.). L - lifetime measurements (including Hanle-effect). H - anomalous dispersion (hook) measurements. M - miscellaneous experimental methods (for example, Stark effect, astrophysical measurements, etc.). OTHER: C - additions or suggested revisions to data in previous articles, comments on particular theoretical or experimental methods, etc. Cp - data compilations. R - relative (non-absolute) oscillator strengths have been tabulated.

ATOMIC AND MOLECULAR DATA

F

117

- data on forbidden (i.e., other than electric dipole) transitions have been tabulated.

Also, in Table 1 the references are ordered according to element and stage of ionization. For brevity, the references are identified there only by the running number of the reference list. Several groups have communicated their work in progress. At the Center for Astrophysics, Cambridge, Massachusetts, f-value measurements are in progress on Co I, V I and Si I. For Co I, the results of hook-method studies in absorption done at Cambridge are being combined with branching-ratio emission measurements carried out by W. Whaling, California Institute of Technology in order to provide data for 360 lines. For V I, a similar combined absorption-emission study is being carried out by the same researchers for approximately 210 transitions; this work is nearing completion. For Si I, oscillator strengths are being measured for about 70 lines in the range 1650 to 2000 A by the hook method. Also, the principal intersystem transition of Mg I is being studied by the Cambridge group with a novel laser-excitation technique. R. Garstang of the Joint Institute for Laboratory Astrophysics, Boulder, has completed his work on Tc lines. At NBS, Washington, transition probability measurements in emission are under way for C I. References 1. 2.

3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

Fuhr, J.R., Martin, G.A., Wiese, W.L., Younger, S.M.: 1981, J. Phys. Chem. Ref. Data 10, p. 305. Wiese, W.L., Martin, G.A.: 1981, "Handbook of Chemistry and Physics," 62nd ed., edited by R. C. Weast and M. J. Astle, Chemical Rubber, Boca Raton, FL, p. E335; and, 1980, Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. (U.S.) 68, Part II (U.S. Government Printing Office, Washington, D.C.). Wiese, W.L., Fuhr, J.R.: 1975, J. Phys. Chem. Ref. Data 4, p. 263. Younger, S.M., Fuhr, J.R., Martin, G.A., Wiese, W.L.: 1978, J. Phys. Chem. Ref. Data 7, p. 495. Smith, M.W., Wiese, W.L.: 1973, J. Phys. Chem. Ref. Data 2, p. 85. Miller, B.J., Fuhr, J.R., Martin, G.A.: 1980, Bibliography on Atomic Transition Probabilities (November 1977 through March 1980), Nat. Bur. Stand. (U.S.) Spec. Publ. 50S, Supple I, U.S. Government Printing Office, Washington, D.C. Aashamar, K., Luke, T.M., Talman, J.D.: 1981, J. Phys. B 14, p. 803. Q Adams, D.L., Whaling, W.: 1981, J. Opt. Soc. Am. 71, p. 1036. ER Adams, D.L., Whaling, W.: 1981, J. Quant. Spectre Rad. Transf. 25, p. 233. ER,C Aeschliman, D.P.: 1981, J. Quant. Spectre Rad. Transf. 25, p. 221. E Anderson, E.M., Anderson, E.K., Eglais, M.O.: 1980, Akad. Nauk. SSSR, Otd. Obshch. Fiz. Astron., Nauch. Sov. Spectrosk., "Spectroscopy of Multicharged Ions," Moskva, p. 138. Q Aspect, A., Imbert, C., Roger, G.: 1980, Opt. Commun. 34, p. 46. E Bachor, H.-A., Kock, M.: 1980, J. Phys. B 13, p. L369. H Bachor, H.-A., Kock, M.: 1980, J. Phys. B 13, p. 2497. H,HR Baessler, P., Kock, M.: 1980, J. Phys. B 13, p. 1351. E Baluja, K.L., Burke, P.G., Kingston, A.E.: 1980, J. Phys. B 13, p. 4675. Q Baluja, K.L., Doyle, J.G.: 1981, J. Phys. B 14, p. L11. QF Baluja, K.L., Hibbert, A.: 1980, J. Phys. B 13, p. L327. Q Bashkin, S., Astner, G., Mannervik, S., Ramanujam, P.S., Scofield, M., Huldt, S, Martinson, I.: 1980, Phys. Scr. 21, p. 820. L Baudinet-Robinet, Y., Dumont, P.D., Garnir, H.P., Grevesse, N., Biemont, E.: 1980, J. Opt. Soc. Am. 70, p. 464. L Beck, D.R.: 1981, Phys. Rev. A 23, p. 159. QF Becker, U., Kerkhoff, H., Kwiatkowski, M., Schmidt, M., Teppner, U., Zimmermann, P.: 1980, Phys. Lett. A 76, p. 125. Becker, U., Kerkhoff, H., Schmidt, M., Zimmermann, P.: 1981, J. Quant. Spectre

118

24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62.

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Rad. Transf. 25, p. 339. L Becker, U., Kwiatkowski, M., Teppner, U., Zimmermann, P.: 1980, J. Phys. B 13, p. 2505. L Berrington, K.A., Burke, P.G., Dufton, P.L., Kingston, A.E.: 1977, J. Phys. B 10, p. 1465. Q Bhadra, K., Henry, R.J.l>l.: 1980, Astrophys. J. 240, p. 368. Q Bhatia, A.K., Doschek, G.A., Feldman, U.: 1980, Astron. Astrophys. 86, p. 32. Q

Bhatia, A.K. , Feldman, U. , Doschek, G.A. : 1980, J. Appl. Phys. 51, p. 1464. Q,QF Bhatia, A.K. , Kastner, S .0. : 1980, Sol. Phys. 65, p. 181. Q,QF Bhatia, A.K. , Kastner, S .0. : 1980, J. Quant. Spectr. Rad. Transf. 24, p. 53. Q,QF Bhatia, A.K., Mason, H.E.: 1980, Astron. Astrophys. 83, p. 380. Q,QF Bideau-Mehu, A., Guern, Y., Abjean, R., Johannin-Gi11es, A.: 1981, J. Quant. Spectr. Rad. Transf. 25, p. 395. M Blackwell, D.E., Pet ford, A.D., Shal1is, M.J., Simmons, G.J.: 1980, Mon. Not. R. Astron. Soc. 191, p. 445. A Borge, M.J.G., Campos, J.: 1980, J. Quant. Spectr. Rad. Transf. 24, p. 263. L Boyd, R.W., Dodd, J.G., Krasinski, J., Stroud, C.R., Jr.: 1980, Opt. Lett. 5, p. 117. L Brandenberger, J.R., Rose, B.R.: 1981, Opt. Commun. 36, p. 453. L Brillet, L., Safronova, U.I., Safronova, A.S.: 1980, Opt. Spectrsc. (USSR) 48, p. 231. I Bromage, G.E.: 1980, Astron. Astrophys., Suppl. Ser. 41, p. 79. Q Brooks, R.L., Pinnington, E.H.: 1980, Phys. Rev. A 22, p. 529. L Brzezowska, J.: 1980, Acta Phys. Pol. A 58, p. 647. Q Buchet, J.P., Buchet-Poulizac, M.C., Ceyzeriat, P.: 1980, Phys. Lett. A 77, p. 424. L Buchet, J.P., Buchet-Poulizac, M.C., Denis, A., Desesquelles, J., Druetta, M.: 1980, Phys. Rev. A 22, p. 2061. L Bunge, C.F.: 1981, J. Phys. B 14, p. 1. Q Cardon, B.L., Parkinson, W.H., Tomkins, F.S.: 1980, J. Opt. Soc. Am. 70, p. 1372. H Catherinot, A., Dubreuil, B.: 1981, Phys. Rev. A 23, p. 763. E Chang, E.S., Sakai, H.: 1981, J. Phys. B 14, p. L391. Q Chang, R.S.F., Setser, D.H.: 1980, J. Chem. Phys. 72, p. 4099. L,E Cheng, K.T., Kim, Y.-K., Desclaux, J.P.: 1979, At. Data Nucl. Data Tables 24, p. 111. Q, QF Chichkov, B.N., Shevelko, V.P.: 1981, Phys. Scr. 23, p. 1055. Q Chung, K.T.: 1981, Phys. Rev. A 23, p. 2957. Q Clyne, M.A.A., Jaffe, S., Whitefield, P.D.: 1980, J. Chern. Soc., Faraday Trans. 2 76, p. 369. A Cohen, M., McEachran, R.P.: 1980, Atomic Hartree-Fock Theory, "Advances in Atomic and Molecular Physics," Vol. 16, p. 1. (eds., D.R. Bates and B. Bederson, Acad. Press, NY). Q Cohen, M., Nahon, J.: 1980, J. Phys. B 13, p. 4325. Q Cowan, R.D.: 1981, J. Opt. Soc. Am. 71, p. 60. Q Danzmann, K., Kock, M.: 1980, J. Phys. B 13, p. 2051. E,H Diebold, G.J., Rivas I.V., Shafeizad, S., McFadden, D.L.: 1980, Chern. Phys. 52, p. 453. LF Diffenderfer, R.N., Dagdigian, P.J., Yarkony, D.R.: 1981, J. Phys. B 14, p. 21. Q,QF Driker, M.N., Ivanov, L.N.: 1980, Opt. Spectrsc. (USSR) 49, p. 229. Q Dufton, P.L., Hibbert, A.: 1981, Astron. Astrophys. 95, p. 24. Q Dumont, P.D., Garnir, H.P., Baudinet-Robinet, Y., Kapenyak, M.: 1981, J. Opt. Soc. Am. 71, p. 502. L Duquette, D.W., Salih, S., Lawler, J.E.: 1981, Phys. Lett. A 83, p. 214. L Eidelsberg, M., Crifo-Magnant, F., Zeippen, C.J.: 1981, Astron. Astrophys.,

ATOMIC AND MOLECULAR DATA

63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112.

119

Supp1. Ser. 43, p. 455. QF Eissner, W., Zeippen, C.J.: 1981, J. Phys. B 14, p. 2125. QF Engstrom, L., Denne, B., Ekberg, T.O., Jones, K.W., Jupen, C., Litzen, U., Meng, W.T., Trigueiros, A., Martinson, I.: 1980, University of Lund, Atomic Spectroscopy, Annual Report, p. 32. L Farrag, A., Luc-Koenig, E., Sinze11e, J.: 1979, At. Data Nuc1. Data Tables 24, p. 227. I Farrag, A., Luc-Koenig, E., Sinze11e, J.: 1980, J. Phys. B 13, p. 3939. I Fawcett, B.C., Ridgeley, A.: 1981, J. Phys. B 14, p. 203. Q Fawcett, B.C., Ridgeley, A., Ekberg, J.O.: 1980, Phys. Scr. 21, p. 155. Q Feldman, P.D., Anderson, D.E., Jr., Meier, R.R., Gentien, E.P.: 1981, J. Geophys. Res. 86, p. 3583. MR Feldman, U., Doschek, G.A., Cheng, C.-C., Bhatia, A.K.: 1980, J. App1. Phys. 51, p. 190. Q,QF Fischer, C.F.: 1978, Technical Report No. COO-4264-4, The Pennsylvania State University Park, PA. Q Fischer, C.F.: 1980, Phys. Rev. A 22, p. 551. I Fischer, C.F.: 1981, Phys. Scr. 23, p. 38. Q,I Fischer, C.F., Glass, R.: 1980, Phys. Scr. 21, p. 525. Q Fujimoto, T., Kato, T.: 1981, Astrophys. J. 246, p. 994. Q,QF Galan, M., Bunge, C.F.: 1981, Phys. Rev. A 23, p. 1624. Q Gallagher, T.F., Sandner, W., Safinya, K.A~: 1981, Phys. Rev. A 23, p. 2969. L Ganas, P.S.: 1979, Phys. Lett. A 73, p. 161. Q Ganas, P.S.: 1979, Astron. Astrophys., Supp1. Ser. 38, p. 313. Q Q Ganas, P.S.: 1980, Int. J. Quantum Chern. 17, p. 1179. Ganas, P.S.: 1981, Opt. Commun. 36, p. 193. Q Q Ganas, P.S.: 1981, J. App1. Phys. 52, p. 19. Ganas, P.S.: 1981, J. App1. Phys. 52, p. 3769. Q Ganas, P.S.: 1981, J. Opt. Soc. Am. 71, p. 908. Q Ganas, P.S.: 1981, Int. J. Quantum Chern. 19, p. 729. Q Ganas, P.S., Green, A.E.S.: 1980, J. Chern. Phys. 73, p. 3891. Q Glass, R.: 1979, J. Phys. B 12, p. 689. Q Glass, R.: 1980, J. Phys. B 13, p. 15. Q Glass, R.: 1980, J. Phys. B 13, p. 899. Q Glass, R.: 1981, Z. Phys. A 299, p. 15. Q Glass, R.: 1981, J. Phys. B 14, p. L409. Q,QF Glass, R.: 1981, Phys. Scr. 23, p. 24. Q Godefroid, M., Verhaegen, G.: 1980, J. Phys. B 13, p. 3081. Q,QF Goldman, S.P., Drake, G.W.F.: 1981, Phys. Rev. A 24, p. 183. Q Go1y, A., Weniger, S.: 1980, J. Quant. Spectr. Rad. Transf. 24, p. 335. E Go1y, A., Weniger, S.: 1981, J. Quant. Spectr. Rad. Transf. 25, p. 381. E Greene, C.H.: 1981, Phys. Rev. A 23, p. 661. Q Gruzdev, P.F., Afanaseva, N.V.: 1980, Opt. Spectrosc. (USSR) 49, p. 341. Q Gruzdev, P.F., Loginov, A.V.: 1980, Opt. Spectrosc. (USSR) 48, p. 242. Q Guern, Y., Lotrian, J.: 1980, J. Quant., Spectr. Rad. Transf. 24, p. 133. E Gurtovenko, E.A., Kostik, R.I.: 1981, Astron. Astrophys. 101, p. 132. C Haak, H.K., Zetzsch,. C., Stuh1, F.: 1980, Z. Naturforsch, Tei1 A 35, p. 1337. E Hannaford, P., Lowe, R.M.: 1981, J. Phys. B14, p. L5. L Hartman, D.C., Hollingsworth, W.E., Winn, J.S.: 1980, J. Chem. Phys. 72, p. 833. E Hata, J., Grant, I.P.: 1981, J. Phys. B 14, p. 2111. Q,QF Hibbert, A.: 1980, J. Phys. B 13, p. 1721. Q,QF Hibbert, A., Bates, D.R.: 1981, Planet. Space Sci. 29, p. 263. Q Hoyls, A., Fuhr, J.R.: 1980, Astron. Astrophys. 90, p. 14. E Huang, C.-M., Wang, C.C.: 1981, Phys. Rev. Lett. 46, p. 1195. A Huber, M.C.E., Sandeman, R.J.: 1980, Astron. Astrophys. 86, p. 95. H,A Hultberg, S., Liljeby, L., Lindgard, A., Mannervik, S., Veje, E.: 1981, Phys. Scr. 22, p. 623. L Jacques, C., Knystautas, E.J., Drouin, R., Berry, H.G.: 1980, Can. J. Phys. 58,

120

113. 114. 115. 116. 117. 118. 119. 120. 121. 122. 123. 124. 125. 126. 127. 128. 129. 130. 131. 132. 133. 134.

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p. 1093. L Jamieson, M.J., Watts, R.S.: 1980, Chem. Phys. Lett. 76, p. 287. Q Jauregui, R., Bunge, C.F.: 1981, Phys. Rev. A 23, p. 1618. Q Jitschin, W., Meisel, G.: 1980, Z. Phys. A 295, p. 37. L Johnson, W.R., Lin, C.D., Cheng, K.T., Lee, C.M.: 1980, Phys. Scr. 21, p. 409. Q

Kafatos, M., Lynch, J.P.: 1980, Astrophys. J. Supp1. Ser. 42, p. 611. CpF Karazija, R.J., Kucas, S.A.: 1979, Sov. Phys.--Collect. 19, p. 20. Q Karwowski, J., Szulkin, M.: 1979, Acta Phys. Pol. A 56, p. 835. Q Karwowski, J., Szu1kin, M.: 1981, J. Phys. B 14, p. 1915. Q Kastner, S.O.: 1980, J. Opt. Soc. Am. 70, p. 1550. I,IF Kato, T.: 1976, Astrophys. J., Supple Ser. 30, p. 397. I Kelly, F.M., Mathur, M.S.: 1980, Can. J. Phys. 58, p. 1004. L Kelly, F.M., Mathur, M.S.: 1980, Can. J. Phys. 58, p. 1416. L Kelly, H.P.: 1975, "Atomic Inner Shell Processes," Vol. 1, Ch. 8, p. 331 (ed., B. Craseman, Academic Press, NY). Q Kerkhoff, H., Micali, G., Werner, K., Wolf, A., Zimmermann, P.: 1981, Z. Phys. A 300, p. 115. L Kerkhoff, H., Schmidt, M., Zimmermann, P.: 1980, Z. Phys. A 298, p. 249. L Khristenko, S.V.: 1976, Phys. Lett. A 59, p. 202. Q Ko1oshnikov, G.V., Kononov, E. Ya., Plotkin, M.E., Ragozin, E.N., Safronova, U.I.: 1980, Sov. J. Quantum Electron. 10, p. 1228. Q Krylov, B.E., Koz1ov, M.G.: 1979, Opt. Spectrosc. (USSR) 47, p. 579. A Kup1iauskis, Z.I.: 1980, Opt. Spectrosc. (USSR) 48, p. 119. Q Lawson, K.D., Peacock, N.J., Stamp, M.F.: 1981, J. Phys. B 14, p. 1929. Q,QF Liljeby, L., Lindgard, A., Mannervik, S., Veje, E., Jelenkovic, B.: 1980, Phys. Scr. 21, p. 805. L Lindgard, A., Mannervik, S., Je1enkovic, B., Veje, E.: 1981, Z. Phys. A 301, p. 1.

L

135. Livingston, A.E., Pinnington, E.H., Irwin, D.J.G., Kernahan, J.A., Brooks, R.L.: 1981, J. Opt. Soc. Am. 71, p. 442. L 136. Loginov, A.V., Gruzdev, P.F.: 1979, Opt. Spectrosc. (USSR) 47, p. 576. Q 137. Luc-Koenig, E., Bachelier, A.: 1978, J. Phys. (Paris) 39, p. 1059. QR 138 Luke, T.M.: 1981, Phys. Scr. 23, p. 1066. Q 139. Malinovsky, M., Dubau, J., Sahal-Brechot, S.: 1980, Astrophys. J. 235, p. 665. Q

140. Mannervik, S.: 1981, Phys. Scr. 22, p. 575. L 141. Mannervik, S., Martinson, I., Jelenkovic, B.: 1981, J. Phys. B 14, p. L275. L 142. Marek, J., Munster, P.: 1980, J. Phys. B 13, p. 1731; 1981, J. Phys. B 14, p. 201. L 143. Markiewicz, E., McEachran, R.P., Cohen, M.: 1981, Phys. Scr. 23, p. 828. Q 144. Mason, H.E., Storey, P.J.: 1980, Mon. Not. R. Astron. Soc. 191, p. 631. Q 145. Mathur, M.S., Kelly, F.M.: 1980, J. Phys. Chem. 84, p. 1783. L 146. Mendoza, C.: 1981, J. Phys. B 14, p. 397. Q 147. Merkelis, G.V., Savichjus, E.G., Kanyauskas, Yu.M., Rudzikas, Z.B.: 1980, Akad. Nauk. SSSR, Otd. Obshch. Fiz. Astron., Nauch. Sov. Spektrosk., "Spectroscopy of Multi-charged Ions," Moskva, p. 65. Q,QF 148. Meyer, G., Ruland, W., Sahm, A., Putlitz, G.zu.: 1981, Astron. Astrophys. 95, p. 278. L 149. Migda1ek, J.: 1980, J. Phys. B 13, p. L169. Q 150. Moore, R.A., Reid, J.D., Hyde, W.T., Liu, C.F.: 1981, J. Phys. B 14, p. 9. Q 151. Morrison, D., Christensen, A.B., Cunningham, A.J.: 1981, J. Geophys. Res. 86, p. 3589. ER 152. Nussbaumer, H.: 1980, Opt. Lett. 5, p. 222. Q 153. Nussbaumer, H., Storey, P.J.: 1980, Astron. Astrophys. 89, p. 308. Q,QF 154. Nussbaumer, H., Storey, P.J.: 1981, Astron. Astrophys. 96, p. 91. Q,QF 155. Nussbaumer, H., Storey, P.J.: 1981, Astron. Astrophys. 99, p. 177. Q,QF 156. Oboladze, N.S., Safronova, U.I.: 1980, Opt. Spectrsc. (USSR) 48, p. 469. QF 157. Osipowicz, A., Werth, G.: 1981, Opt. Commun. 36, p. 359. ER

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158. Pasternack, L., Silver, D.M., Yarkony, D.R., Dagdigian, P.J.: 1980, J. Phys. L,QF B 13, p. 2231. 159. Peterkop, R.K.: 1980, Latv. PSR Zinat. Akad. Vestis, Fiz. Teh. Zinat. Sere No. 160. 161. 162. 163. 164. 165. 166. 167. 168. 169. 170. 171. 172. 173. 174. 175. 176. 177. 178. 179. 180. 181. 182. 183. 184. 185. 186. 187. 188. 189. 190. 191. 192. 193. 194. 195. 196. 197. 198.

1, p. 3.

Q

Pindzola, M.S., Bhatia, A.K., Temkin, A.: 1980, Phys. Rev. A 22, p. 132. Q Pindzola, M.S., Carter, S.L.: 1980, Phys. Rev. A 22, p. 898. Q Pirronello, V., Strazzulla, G.: 1980, Astrophys. Space Sci. 72, p. 55. Q Pradhan, A.K., Norcross, D.W., Hummer, D.G.: 1981, Phys. Rev. A 23, p. 619. Q Rothenberg, J.E., Harris, S.E.: 1981, IEEE J. Quantum Electron. 17, p. 418. Q Safronova, U.I.: 1980, Akad. Nauk. SSSR, Otd. Obshch. Fiz. Astron. Nauch. Sov. Spektrosk., "Spectroscopy of Multi-charged Ions," Moskva, p. 101. Q Safronova, U.I., Lisina, T.G.: 1979, At. Data Nucl. Data Tables 24, p. 49. Q Safronova, U.I., Safronova, A.S.: 1980, Opt. Spectrsc. (USSR) 48, p. 121. I Safronova, U.I., Senashenko, V.S.: 1977, J. Phys. B 10, p. L271. Q Safronova, U.I., Senashenko, V.S.: 1981, J. Phys. B 14, p. 603. Q Safronova, U.I., Urnov, A.M.: 1980, J. Phys. B 13, p. 869. Q Saha, S.C., Sengupta, S.: 1981, Z. Naturforsch., Teil A 36, p. 272. Q Sampson, D.H., Clark, R.E.H.: 1980, Astrophys. J., Supple Sere 44, p. 169. Q Sampson, D.H., Clark, R.E.H., Golden, L.B.: 1980, Astrophys. J., Supple Sere 44, p. 193. Q Saraph, H.E.: 1980, J. Phys. B 13, p. 3129.Q Saraph, H.E., Seaton, M.J.: 1980, Mon. Not. R. Astron. Soc. 193, p. 617. Q Schulz-GuIde, E., Wenzel, A.: 1980, J. Phys. B 13, p. 3733. E,ER Senashenko, V.S., Simonov, G.A.: 1980, J. Appl. Spectrsc. (USSR) 32, p. 76. QF Shull, J.M., Snow, T.P., Jr., York, D.G.: 1981, Astrophys. J. 246, p. 549. M Siefart, E.: 1980, Ann. Phys. (Leipzig) 37, p. 143. Q Silverans, R.E., Borghs, G., DeBisschop, P., Van Hore, M., Van den Cruyce, J.-M.: 1981, J. Phys. B 14, p. LIS. L Stanton, A.C., Kolb, C.E.: 1980, J. Chem. Phys. 72, p. 6637. LF Steenman-Clark, L., Bely-Dubau, F., Faucher, P.: 1980, Mon. Not. R. Astron. Soc. 191, p. 951. Q L Thomas, P., Campos, J.: 1980, An. Fis. 76, p. 23. Trabert, E., Heckmann, P.H.: 1980, Phys. Scr. 21, p. 35. L Trabert, E., Heckmann, P.H.: 1980, Phys. Scr. 21, p. 146. L Trabert, E., Heckmann, P.H.: 1980, Phys. Scr. 22, p. 489. L Trabert, E., Heckmann, P.H., Schlagheck, W., Buttlar, H.V.: 1980, Phys. Scr. 21, p. 27. L Vajed-Samii, M., Ton-That, b., Armstrong, L., Jr.: 1981, Phys. Rev. A 23, p. 3034. Q,QF,I,IF Whitkop, P.G., Wiesenfeld, J.R.: 1980, Chem. Phys. Lett. 69, p. 457. L Wosinski, L.: 1981, Acta Phys. Pol. A 59, p. 543. E Wujec, T., Weniger, S.: 1981, J. Quant. Spectre Rad. Transf. 25, p. 167. E Wyngaarden, W.L. van, Henry, R.J.W.: 1981, Astrophys. J. 246, p. 1040. Q Wynne, J.J., Beigang, R.: 1981, Phys. Rev. A 23, p. 2736. MR Younger, S.M.: 1980, Phys. Rev. A 21, p. 1364. Q Younger, S.M.: 1980, J. Quant. Spectre Rad. Transf. 23, p. 489. Q Zeippen, C.J.: 1980, J. Phys. B 13, p. L485. QF Zhechev, D.: 1980, Opt. Spectrsc. (USSR) 49, p. 253. L Zizak, G., Horvath, J.J., Van Dijk, C.A., Winefordner, J.D.: 1981, J. Quant. Spectre Rad. Transf. 25, p. 525. M

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122

TABLE

1

Selected references on atomic transition probabilities (numbers in parentheses correspond to references 7-198) Ag I (49)

Cd II (49)

Al Al Al Al

Sequence (73) I (72,103) III (49) X (186)

C1 Sequence (83)

Ar Ar Ar Ar Ar Ar Ar Ar

I (8,15,32,34,56) II (8,15) III (1l8) V (135) VI (135) VII (135) VIII (135) IX (1l6)

Au I (49) B Sequence (48,65,66, 156,165,188) B I (52,53) B II (138) Ba I (13,77,115,124, 145,159) Ba II (49,148, 157,180) Be Sequence (48,87, 116,131,143,147, 156,165,166,170, 173,195) Be I (52,97) Be II (76,125,141) C C C C

Sequence (48,165) I (52) II (53,117,154) III (21,25,122) C IV (112) C V (112) Ca I (12,57,103,123, 124,158,189,193) Ca II (49) Ca VII (122) Ca IX (122) Ca XI (58) Ca XII (122) Ca XIII (122) Ca XIV (122,129) Ca XV (122,129) Ca XVI (122,129) Ca XVII (122,129)

Co Co Co Co Co Co Co Co

VIII (68) XIX (132) XX (132) XXI (132) XXII (132) XXIII (132) XXIV (132) XXV (132)

Cr Cr Cr Cr Cr Cr Cr Cr Cr

I (103,191) II (95,191) XVI (70) XVII (70,132) XVIII (70,132) XIX (70,132) XX (70) XXI (70) XXII (132)

Cs Sequence (120) Cs I (49,150) Cu I (49,126,197) Cu II (21,74) Cu X (68) Eu I (148) Eu II (148) F Sequence (37,48,147, 156,165,170) F I (176,181) F II (176) Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe' Fe Fe Fe Fe

I (9,33,101,103) II (153) X (58,117,139) XI (117) XII (117,122) XIII (117) XIV (71,117) XV (29,30) XVI (42) XVIII (42,70,122) XIX (42,70,122,132) XX (31,129) XXII (88,89,144) XXIII (70,91) XXIV (132) XXV (161)

Ga I (134,198) Ga III (49,134) H Sequence (94) He Sequence (93,105,113, 116,122,128,163,168, 169,172) He I (39,45,82,171) Hf IV (149) Hg

II (49)

In I (130) In III (49) K Sequence (120) K I (10,49,109,150,164) Kr I (32,56) Kr XXXV (161) Li Sequence (48,119,120, 156,165,167,168,177) Li I (21,35,43,49,50,80, 114,140,152,164) Li II (76,140,160) Lu III (149) Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg Mg

Sequence (11,116,195) I (7,124,133,145) II (49,133,146) III (41) IV (41,117,122) V (41,117,122) VI (117,122) VII (117,122) VIII (117,122) IX (185,186) X (122,182,185) XI (185,186)

Mn I (24) Mo I (61) N Sequence (48,62,85, 156,165,170) N I (46,51,56,117) N II (59,107,117) N III (53, ll7) N IV (64,122,194)

123

ATOMIC AND MOLECULAR DATA

Na Sequence (98,120) Na I (49,103,150,183) Na II (136) Ne Ne Ne Ne Ne Ne Ne Ne Ne

Sequence (11,86,121) I (32,36,47,56,102,190) II (117) III (117) IV (117) V (16,117) VI (117,122) VII (92,194) VIII (122)

Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni

I (23,104,110) IX (68) X (122) XII (38,122) XIII (38,122) XIV (38,122) XV (38,122) XVI (122) XVII (29,30,122) XIX (122) XX (70,122) XXI (70,122,132) XXII (70,122,132) XXIII (70,122,132) XXIV (70,122,132) XXV (70,122) XXVI (122,132) XXVII (122)

o Sequence (48,165,170) o I (56,117) o II (63,69,117,151,196) o III (17,79,117,155,175) o IV (53,78,117,174) o V (25,64,90,106) o VII (75) P P P P P P P

Sequence (84-) III (40,72) IV (99) IX (184) X (184) XI (67,184) XII (67,184,186)

Rb Sequence (120) Rb I (49,137,142,150) S S S S S S S

I (54,176) II (117,176) III (117) IV (26,27,72,117) V (192) VII (58,99) VIII (117,122)

S S S S S S

IX (117,122) X (117,122,186) XI (117,122,186) XII (117,122,186) XIII (186) XIV (122)

Zn Sequence (195) Zn I (21,127) Zn II (49,111) Zr I (103) Zr II (103, 162)

Sb I (100) Sc I (179) Si Si Si Si Si Si Si Si Si Si Si Si

I (19,22,81) II (19,72,117,178) III (18,19) IV (19) V (122) VI (117,122) VII (117,122) VIII (117,122,187) IX (117,187) X (117,122,187) XI (186) XII (122)

Sr I (124) Sr II (49~ Ti I (14,108) Ti II (55) Ti III (20,21) Ti IV (20,60) Ti V (20,60) Ti VI (60) Ti VII (60) Ti XIV (28) Ti XV (28) Ti XVI (28,129) Ti XVII (28) Ti XVIII (28) Ti XIX (28) Ti XX (28) Tl I (134) TI III (134)

V II (96) V VII (38) V VIII (38) V IX (38) V X (38) Xe I (32,56) Xe II (180) Y I (44) Y II (162) Yb II (149)

W.L. Weise Chairman of Working Group

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124

WORKING GROUP 3:

14

COLLISION CROSS SECTIONS AND LINE BROADENING A.

Line Broadening

The most recent state of advances in the subject can be found in the 1980 Proceedings of the Sth International Conference on Spectral Line Shapes(l). In(2), Breene has reformulated basic theories of line broadening in a modern point of view. Review papers have been written: in(3) the emphasis is upon atomic lines broadened by electron and positive ions but some neutral atom broadening is discussed; (4)-(16) concern neutral atom broadening and the related topic of the interatomic potential. 1.

Stark Broadening of Hydrogen or Hydrogenic Lines

Concerning the center of hydrogen lines, the difficult problem of ion dynamics (colliding ions are neither "impact" nor "quasi-static") dominates the actual preoccupations «l)pp. 3-102,(7), (8)). A comprehensive discussion of the underlying physics supporting the model microfield method (M.M.M. has been done(9) and different model microfields have been used in calculations(l). Three effects of ion dynamics have been displayed(ll). A numerical simulation has been performed(12) and the results agree within 10% with the M.M.M. Correlation effects between Doppler and Stark broadening have also been suggested(13). New experiments testing ion dynamic effects have been performed (Ha He Hy) for the whole profiles(14-l7) and for the shifts(18) (Ha, Da: no effect in that case).

6

In fact the inclusion of ion dynamics in the theories has greatly reduced but not eliminated all the observed differences. For explaining the remaining discrepancies, a model has been proposed which includes effects from electron producing low-frequency fields and has been applied to LYa(19) and LYS(20) with equally satisfactory agreement with experiment(2l). Impact theories have been found to be correct for Ha fine structure transitions at very low densities (108 - lOll cm- 3 ). Concerning the wings of hydrogen lines, attention has been directed towards the satellite structures which appear as superimposed on the line profile: the role of hydrogen molecular lines has been evinced experimentally for Hs(23) and improved calculations, including H2+ molecular potential, have been provided for LYa(24). The contribution of electron collisions to the wings of Hs have been calculated with the dipolar exact resonance quantum theory(2S) and the derived asymmetry is in agreement with earlier experiments. Hydrogenic ion line profiles have been studied t especinlly in view of spectroscopic diagnostic in very dense and hot plasmas «l)p. 29S-432 and lS3-l66). An exact quantum analytic solution of the problem of line broadening for hydrogen like ions by electrons has been obtained in the dipole approximation(26). Measurements of polarization shifts have shown the insufficiency of previous theoretical estimates(27). Effects of fine structure splitting have been studied(28,(29). An impact theory of spectral line broadening has been developed for transitions between degenerate states and for anisotropic collisions(30). 2.

Stark Broadening of Overlapping Lines of Helium

Ion dynamics are also important and have been taken into account in two ways(3l,32) and the M.M.M. gives the best agreements with the experiments(33-36). Effects of molecular He2 structure have been detected in the wings(37). For stellar spectra studies, improved M.M.M. line profiles have just been provided(38). 3.

Stark Broadening of Isolated lines

No revolutionary results have been obtained during that period, but a number of

ATOMIC AND MOLECULAR DATA

125

new data of astrophysical interest have become available: impact and semi-classical (S.C.) or semi-empirical (S.E.) theories have been applied and numerous experiments (E) have been performed (Table I). Attempts are made for providing simple but reliable formulae, especially for higher ionization stages«l)pp. 191, 211, (40), (47),(51», but also for neutral emitters(60). One can point out the first observations of ion dynamic effects in helium isolated line profiles consistent with calculations based on an adiabatic unified theory for ion perturbers(35). A detailed comparison between quantum and semi-classical calculations has been made on the example of Li I 2s-2p, evincing the break down at very low temperatures of the validity of the semi-classical treatment as expected(42). j-~ coupling has been introduced for lines of heavy elements showing departures from L.S. coupling(61). Improvements to straight path S.C. theory has been proposed, taking classically into account the back reaction of the neutral emitter on the perturbing electron(62). Systematic trends in Stark widths of isoelectronic sequences have been examined «63),(1)p. 241). An attempt to predict the line broadening of autoionizing levels by electric fields has been elaborated and applied to A I «l)p. 281). 4.

Line Broadening by Foreign Gases and Resonance Broadening

A great deal of attention has been paid to atomic line broadening «l)pp. 593757) and to related topic of excimers «l)pp. 767-826). Recent experimental and theoretical data concerning the impact broadening and shift of atomic lines broadened by the perturbers of astrophysical interest, atomic hydrogen(67),(68) or helium(67),(69)-(82) are collected in Table 2; (84) concerns high pressure non impact results, and (85)-(87) refer to molecular rotational or vibrational components and lines of OH and CO. The increased precision of the measurements of the two past years indicates many discrepancies of as much as 25% with the theory, evincing again the drastic influence of the interatomic potential. The different broadening of fine structure lines is generally well predicted and the effects of the various collisional coupling become to be very clearly understood(76). Hyperfine structure effects have been shown for the first time(69), leading to a collisional narrowing effect due to the H.F.S. decoupling at very low densities. In light of these considerations the simple formulae obtained in (88),(89) for line broadening by neutral hydrogen must be used with caution, since the interatomic potential used takes only into account the overlap of the atomic charge distribution and neglect shorter range interactions which should be important. The numerous works «l)pp. 827-866) which concern resonance broadening are not reported here, since their interest is far from direct astrophysical applications. The same remark concerns the topic of excimers: it is a very exciting branch of the study of line profiles and extreme line wings in connection with the asymptotic behaviour of the interaction potential of the quasimo1ecule formed during the collision. The interaction of these collisional processes with the absorbed and emitted radiation processes brings us to the last part of the report. We will quote only (90,91) for showing the future importance of these processes for high resolution spectroscopy of astrophysical spectra. 5.

Collisional Redistribution of Radiation and Related Phenomena

Recent developments in high resolution and high power laser sources have resulted in an increased interest in collisional redistribution of radiation. Astrophysical needs remain numerous and will certainly profit of these progresses. Previous work on the redistribution of weak (excitation may be considered as an independent scattering of separate photons) radiation due to collision, has been extended to situations in which absorption or emission of radiation can occur in the non impact (line wings) of the spectrum(92),(93). It has been shown that inelastic collisions may well redistribute the radiation(94)-(96). The effect of correlations between radiative and collisional events has been included in a consistent way by

COMMISSION 14

126

Table I STARK BROADENING OF ISOLATED LINES

Lines

Range of plasma parameters (Ne cm- 3 , TO K)

References

HeI(12Iines)

(35) E

0.2-1.310 16 ,1.-2.

He I 6678, 5876, 3889

(36) E

10 17 _2 10 18 , 1.-2:, 10 4

He I 3965

(39) E

1.3-1.9 10 16 , 1.5 10 4

He I

(40) S.

(12 lines and 42 lines)

Alkali resonance lines LiI

(45 )

(13 lines)

108 lines from doubly and triply ionized atoms

7.10 15

E,

(40)

S.C.P.

(49) S. E.

Mg I 2852, Mg I I 2795

(50) E

E,

s.

4

E.

Al I (4 lines)

(65) E

o III

(51)S.E. (52) S.c.

I I I (17 lines)

(58) E

Ar I 3949 Sn I 5p-6s, Sn I I (10 lines)

E = Experimental.

, 5.10

S. E., S.C.

Alkali like ions

Xl I (8 lines)

1.4 10 18

212-239, (41),

(48) (53)

S III IIV (17 lines)

Pb I III (8 lines)

,10 4

(66) E

UV

Bi I (3 lines)

2.5 10 3 -2.10 4

S. C.P., C.C.

(1) ~ (59)

from Be to Ar elI

4

(44) E

UV (15 lines)

NIIIIII IIV

, 2.10

(43) E

Fe I 5383 NI

2 10 4

(41) M.M.M. (42)

2s2p

c. P.

104

(54)

I (56) (57) (58)

1. 1-1. 6 10

17

,1.3-1. 4 10

4

1.5-6.10 16 , 1.2 10 4

10 17 , 2.10 4 , 5.10 16 ,2.510 4 1.5-5. 10

16

, 1. 2 10

4

E, (55) S. E.

16 4 5-12 10 , O. 9-1 .2 10

E

4-12 10 16 , 1-1.2 10 4

E

5-13 10 16 , 1.1-1.2 10 4

E

2.2-10 10 16 , 0.9-1.2 10 4

T = Theory; Q = Quantum, B = Born, S.C. = Semi-Classical,

P = Perturbation theory, C.C. = Close Coupling, M.M.M. = Model Microfield Hethod, S.~

=

Semi Empirical.

(fine structure lines) + He

(2

Hor-

He I

4p-7s (f.s. lines) + He

K

(Rydberg states) + He

X2

n

3 /

2

3

( 2"

C 0 + H2 and He (v

C 0 + H2

H

-I>

+ He (4 lines)

Al I

o

(8p-6s) + He

Cs I

+ He

0_ v

5

"2 )

1)

MgI/II, Cal/II, Sr I/ll (F.S. lines) + He

4227, Ca I I H, K, 8542, 8662 + He

Ca I

I-~e

(mul t.

3) +

(42 lines) + He

,

(0) E

Q, S. C., C.C.

7-3.5 10 16 ,

~ 733, E

(87)E

(86)E

(85 )E

( 83 i E

, Q,

C.C.

(84)E, unified theory

(1)

10 17 _10 19 ,

10 15 ,

2 10 16 _10 17

1.5-5 10 19 ,

10 19 _5.10 21 ,

10 18

up to 10 19 ,

0.6 10 16 _10 17

5-15 10 18 ,

3-10 10 17 ,

1-6 10 18 ,

(80) (E) (81)E

Temperature (oK)

310

100,300

300

1350

478

500, 5000

520-800

2000

2000

463

400

450

450

500-2000; 10 17 _10 19 ,450

a.

4.10 19 , 10 4

up to 10 19 ,

(E)

-,

),

3.6-12 10 19 , 5-10 10 3

Density (cm- 3

(81) E

o 9)

(78) E

(82) E

(77) E

(76)

(72)C.C., (74)E, (5)E

(1)E

(69)

(68) E

(67) E

References

COLLISIONAL BROADENING BY FOREIGN GASES

Ca I

Fe I

Rb (D 2 ) + He

Rb

K 4s-4p + He

4s-5p (f.s. lines) + He

K

Na D1 and D2 + He

3p _ 3d 3 D ) P o l + He

+ H

He 5 AU. Ip (1980, A&A 92, 95) analyzed the modification of the outer ion coma due to the inward-streaming solar wind for different size comets at various heliocentric distances. Ip (1979, Planet. Sp. Sci. 27, 121) proposed that, even in the limit of tail magnetic fields < 10 thesubstorm discharge mechanism of Ip and Mendis is capable of producing ionizing currents in the head region. Niedner (1980, Ap. J. 241, 820) found that flares in bright comets with plasma tails tend to occur ar-the times of tail disconnection events. Reconnection in cometary ionospheres at sector boundary crossings was studied by Niedner et al. (1981, Ap. J. 245, 1159). Mendis et al. (1981, Ap. J. in press) examined the bombardment of the nucleus by the solar wind at large heliocentric distances. In their model, the charging of the nucleus can create electric fields capable of causing a large-scale dust blow-off. This may be relevant to flare-ups of cornet P/Schwassman-Wachman I.

-r-,

c. Laboratory and Computer Simulation Studies Laboratory simulations of the comet/ solar-wind interaction have been carried out by podgorny and his·collaborators (1980, Moon and Planets, 23, 323) using a wax sphere of 2.5 cm radius to stimulate a cornet and the hydrogen plasma flow produced by a coaxial electrodynamic accelerator for the solar-wind. Schmidt and Wegman (1982, "Comets") and Fedder, Brecht and Lyon (1981, EOS, Trans. AGU, 62, 367) have used MHD computer codes to stimulate the 3-dimensional floW-and magnetic field profiles in bright comets. COMETARY HALLEY MISSIONS - J. Rahe, H. Fechtig Several missions to intercept Comet Halley are now in preparation. ESA will fly a mission to Halley's comet, called "Giot to" • The spacecraft's design is based on existing Geos spacecraft. It will be launched in July 1985 and fly by the comet in March 1986, about a month after the comet's perihelion passage (February 9, 1986). The encounter duration during which measurements can be performed, lasts four hours. The payload consists of a nucleus imaging camera, an optical probe for coma gas and dust, neutral and ion mass-spectrometer, dust impact detector and mass-spectrometer, electron/ion analyzer, energetic particle detector and magnetometer. The Japanese Institute of Space and Astronautical Science in Tokyo is planning its first interplanetary probe named "Planet-A", to intercept Comet Halley March 8 at 10 krn. It will take

162

COMMISSION 15

Lyman-alpha images of the cornet and measure the solar wind plasma near the comet. Soviet spacecrafts will carry Venus entry probes to the planet's vicinity. and as a result of a Venus swing_by will be inserted into a trajectory to Halley's comet. They will encounter the comet March 8 and 15. Experiments consist of two imaging cameras, a three channel spectrometer for UV, visible and IR, three middle IR radiometers, dust detectors similar to the Giotto exper iment, an ion anal yzer, plasma wave anal yzer, and energy spectrum detector and two magnetometers. COMETARY RESEARCH IN THE USSR - B. Donn Because of a delay in receiving the Soviet contribution this section was prepared by B. Donn using Astronomy and Astrophysics Abstracts deSignation. These compendia provides a comprehensive summary of Soviet publications "Problems of Cosmic Physics" in Russian, contains many papers on comets. minor planets and meteorites. Several stUdies of orbital statistics were carried out by A. S. Demenko (28.102.013). orbits of canetary families; P. 1. Veleshchuk (28.102.048), A. S. Guliev (28.102.049; 25.102.034), v. P. Tomanov (28.102.053), v. v. Rad ziev sky (27.102.034), Y. N. Ivashchenko et al. (27.102.053). Dynamical studies of orbits were published by V. P. Tomanov (27.102.032). V. V. Radzievsky (28.102.051), E. N. Kramer et al. (28.102.053), non-gravitational effects on P/Brorsen-Metcalf by T. A. Vinogradova and V. A. Shor (27.103.201), evolution of orbit of p/Chernykh by E. I. Kazimirchek-polanskaya and N. S. Chernykh (27.103.221). Planetary capture by Jupiter was analyzed by Tomanov (28.102.010) and Kazimirchek-Polanskaya (25.102.008) and for Neptune (25.102.009) • Disintegration of comets was considered by D. A. Andrienka et al. (28.102.012) and O. V. Dobrovolsky (26.102.052). Flares and outbursts were studied by Andrienko and colleagures (28.102.011, 020, 044, 045, 050; 27.102.051, 055). The relation between outbursts and interplanetary magnetic fields was treated by V. A. Golubev (26.102.063). S. K. Vseksvyatsky considered effects of solar plasmoids (26.102.065). V. V. Konopleva and L. M. Shul'man (27.102.046, 049) discussed radii. Composition was considered by Shul'man (26.102.005) and E. J. Kajmakov and I. N. Matveev (26.102.053). Shul'man also treated nuclear structure (26.102.060). Metal atoms in comet heads were discussed by S. Ibadov (28.102.014). Dobrovolsky also re-examined Kreutz's family (26.102.050). Vseksvyatsky examined some current problems (26.102.064) and N•• A. Belyaev treated the rediscovery of lost comets (25.102.003) • LABORATORY RESEARCH - B. Donn Spectroscopic results appear in the Commission 14 Report, attention is called to the comprehensive rev iew by Huber and Herzberg (1979 "Constants of Diatomic Molecules"). Reaction rates for ion-molecule reactions are reviewed by Huntress et al (1980, Ap. J. Suppl. 44, 481). Laboratory photochemistry is discussed by Jackson (1981, Modern Observational Techniques for Comets). Papers on reaction rates, photochemistry and spectroscopy will be found in journals of physical chemistry, chemical physics and spectroscopy. Ultraviolet irradiation of ice mixtures is underway in Greenbergs group at Leiden University (Hagen et al, 1979. Astrophysics and Space Science 65, 215; Greenberg 1982, "Comets") at NASA/Goddard Spacf' Flight Center lMV proton irradiation of cometary type ioe mixtures con' .nues (Donn, 1981, C. P. Colloq; M. H. Moore, 1981, Ph.D. Thesis, U. Marylanc' Astron. Prog.).

COMETS, MINOR PLANETS AND METEORITES

III.

Meteorites

L. L. Wilkening, B. Yu Levin and A. A. Yavnel The numbers of new meteorites recovered by Japanese and American teams in Antarctica continued to climb dramatically. In contrast to the 5-10 meteorites recovered annually from the rest of the earth, the collection rates in Antarctica are 300-3000 samples/year. Two other sources of meteoritic material are also becoming important namely, dust-size particles collected in the stratosphere and meteorite ablation spherules recovered from deep sea sediments. Ordinary chondrites became increasingly popular subjects for study. Chondrules (Lux et al. 1981, Geochim. Cosmochim Acta (GCA) 45, 675; Kimur and Yagi, 1979, Allen et al., 1980, Geochim. Cosmochim. Acta (GCA) 44,1161; Evensen et al., Earth Planet. Sci. Lett. (EPSL), 1979, 42, 222;also proc. Lunar Planet. Sci. conf. 10) matrix (Huss et al. 1981, GCA, 45, 31) and metal phases, Affiatalab and Wasson, GCA, 1980, 44, 431; Woolum etal., LPSC, 9) were all targets of studies which show unequilibrated ordinary chondrites exhibit a range of textures and compositions consistent with their being primitive material. Scott and Rajan studied the petrography and composition of xenoliths in ordinary chondrites (GCA 1981, 45, 53). Chemistry of the L-group chondrites showed existence of possible-Subgroups (Neal et al. GCA 1981,45, 891). Distribution of U and PU in St. Severin was described by Jones and Burnett (1979, GCA 43, 1895). Elemental fractionation among ordinary chondrites was the topic of papers in LPSC 10. Ar-40/Ar-39 dating of shocked chondrites was the subject of papers by Bogard and Hirsch (GCA 1980, 44, 1667) and Turner et al. (LPSC'1978, 9, 978). Chen and Wasserburg measured uranium isotopes in 9 chondrites and found no evidence of excess U-235 reported by others (Geophys. Res. Lett. (GRL) 1980, 7, 275). Origin and evolution of enstatite chondrites were the subjects of several papers (e.g., Biswas et al. GCA 1980, 44, 2097; Larimer and Bartholomay, GCA 1979, 43, 1455; Minster et al., EPSL 1980, 44, 420; Herndon and Rudee EPSL 1978, 41, 101). Carbonaceous chondrites, CM type, have been subject of a nwnber of studies which show them to be less primitive than previously believed (Bunch and Chang, GCA 1980, 44, 1543; Bunch et al. and McSween, GCA 1979, 43, 1727, 1761; Kerridge and Bunch, 1979, Asteroids). Studies of CM matrices-With transmission electron microscopy-were made by Barber, GCA 1981, 45,945). Their chemical composition was studied by McKee and Moore, LPSC 1979, 10, 921. Malysheva et al. (LPSC 10, 977) studied by means of Mossbauer spectroscopy the kinetics of thermal metamorphism of carbonaceous chondrites under different redox conditions. Rare gases in carbonaceous chondrites continue to be the subject of controvery. A series of papers on this topic by Anders, Lewis, Frick and others can be found in the Proceedings of the 9th, 10th, 11th Lunar & Planet. Sci. conf. Shukolykov (Geokhimiya (GEOKH), 1980) proposed a model of primordial Xe in carbonaceous chondrites composed of a mixture of three components. Levskij (MET. 37; 38) found that atomic and isotopic ratios of primordial gases in carbonaceous chondrites were established before the capture of gases by meteoritic matter and that in the Saatov chondrite the planetary rare gasses ( Ar) are concentrated in the light fraction enriched in plagioclase. Zaikowski and Schaeffer (EPSL 1980, 45, 141) showed that the solubility of rare gases in clay minerals was insufficient to account for rare gases in carbonaceous chondrites. Descriptions and analyses of refractory, CA1-rich materials in CM and CV material also occupied the attention of many resarchers. Some of these papers

163

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can be found' in LPSC 9-11, also EPSL (e.g., Macdougall, 42). A number of advances were made in studies of irons, stony-irons and achondrites. Kracher et al. (GCA 1980 44, 773) published a refinement of classification of iron meteorites. Yavnel' (MET 39) from the analysis of distributon, of Co and P between kamacite and taenite showed that equilibation of these two phases occurred in the temperature interval 500-400 0 C. Khodakovskij and petayev (GEOKH, 1981) established differences in the formation conditions of nitrides in meteorites from a thermodynamic analysis of mineral equil ibr ium. Kaiser et al. (GRL 7) found isotopicall y anomalous silver in the Santa Clara and Pinon meteorites, due either to in-situ decay of extinct Pd-l07 or cosmic ray spallation. petrology of igneous clasts in mesosiderites and howardites was described by Mittlefehldt et al. (GCA 1979, 43, 673). Hewins studied the composition of metal in basaltic achondrites cc.;CA 1979, 43, 1663; also LPSC 9. 10. 11). A discordant set of ages of shergottiteS-as measured by Bogard et al. (1979, GCA 43, 1047) and Nyquist et a!. (1979, GCA 43, 1057). Petrology of shergot tites was al so stud ied by Stolper and McSween (GCA 1979 43, 589) and McSween et a!. (EPSL 1980 45, 275). Composi tion and structure of separate minerals from meteor i tes were studied by Kolomenskij et al. (MET 37; Mineralogichesky (MIN) 33, Larvukhina and Korotkova (Lunar Planet. Sci. Abs. (LPS) , XII), Ivanov and-Yudin (MET 37), Pokrovskij et al. (MET., 37), Semenenko et al.-cMET., 38; 39), Yasinskaya and Semenenko (MIN., 33). Some new minerals in sil icate incl usions in the iron meteorite Elga were studied by Osadskij et al. (LPSC, 12, 793). Composition, mineralogy and structure were studied for about ten stones and irons (Barsukova and others, MET., 37, 38, 39). Kuzminskij (Bull. Astron. Inst. Czech. (BAC) , 31, 58) published the results of chemical and mineralogical study of the iron meteorite Morasko (poland). Skripnik and Kirova (MET., 39, 38) determined petrological types for 94 chondrites from the collection of~he USSR Academy of Sciences. Yavnel' (MET., 37; 39) published a critical analysis of modern meteorite classifications. -Chemical criteria for classifications of chonrites and achondrites were supplmented and made more precise. From the study of meteorite radioactivity Luvrukhina and Ustinova (MET., 4; LPSC, 9) found the existence of gradients of galactic cosmic rays. A disturbance in the mecganism of solar modulation of galactic cosmic rays' intenSity about 2-6.10 years was found. It was shown that the integsity of nonmodulated galactic cosmic rays was constant during the last 6.10 years. Lavrukhina and others studied cosmogenic isotropes and tracks in several meteorites and determined their pre-atmospheric sizes (MET., 14, MET., 38). Korotkova et al. (LPSC, 1979 10, 907; MET., 14) showed the presence of two groups of tracks in the olivine from the Allende meteorite -- those from cosmic rays of low energy formed during a pre-accretional irradiation and from spallation fragments. Perelygin and Kasshkarova (MET., 38) from the analysis of tracks and thermoluminescence of several palalasites found that these meteori tes were heated up to 80-200 C for a long time. Nishizumi et al. (EPSL 1981, 52, 31) published data for cosmic ray produced Cl and Mn in Antarctic meteorites. VUV reflection spectra of L, LL, E and sosme achondrites were reported by Wagner et al., in LPSC 1981,11, 775.

COMETS, MINOR PLANETS AND METEORITES

IV.

Minor Planets

Clark R. Chap-nan Introduction In the early 1970'S, serious study of the physical properties of asteroids accelerated rapidly, spurred by the 1971 I.A.U. Colloquium in Tucson. The early and mid-70'S was a period of intensive data collection plus preliminary interpretations and synthesis. At that time, these topics were incorporated into the responsibilities of Commission 15. The past three years have yielded a comprehensive synthesis of the voluminous data that has been consolidated within the TRIAD databank (TRIAD = Tucson Revised Index of Asteroid Data). A second Tucson asteroid meeting, held in March 1979, gave diverse researchers from around the world the chance to compare notes and hypotheses. It resulted in the publication of a new, definitive book, Asteroids (T. Gehrels, Ed., University Arizona Press, 1979). Tabulated in appendices of that book are the complete contents of TRIAD, as of mid-1979. The current version of TRIAD may be acquired in machine-readable form from B. Zellner of the University of Arizona. Since the 1979 conference, there have been further advances in asteroid research. The first phase of an entirely new 8-color photometry program has been completed. Several other kinds of observations, notabl y lightcurve work, have made further strides. Some ideas that were once ridiculed are gaining a measure of acceptance (e.g., possible asteroidal satellites). In the last few years, there has been increasing awareness throughout many scientific and engineering disciplines that asteroids have had an important effect on our planet in epochs past and may serve important utilitarian purposes in the not-too-distant future. The Alvarez et al. hypothesis (Science 208, 1095-1108, 1980) that an asteriod or comet impact was responsible for many-of the species extinctions at the end of the Cretaceous, 65 million years ago, is gaining widespread experimental support and is helping to spur recognition of asteroid impact as a significant force in our own planet's geological and biological history. The proceedings of an October 1981 conference on the topic (Snowbird, Utah) are in press (see Kerr, Science 2 ~, 896-898, 1981). The hypothesis that asteroids are chiefly like meteorites in composition is continuing to gain observational support. This raises the possibility that asteroids, including Earth-approaching objects yet to be discovered, may have potentially valuable quantities of rare siderophile metals and other materials of potential use in space operations. For this reason, asteroid mining is a key linch-pin in the plans and proposals of space activists and futurists. The developing scientific interest in asteroids and comets as remnant planetesimals from primordial epochs, combined with increasing popular interest, has led to further considereation of spacecraft missions to asteriods in several countries. (1980, "Strategy for the Exploration of Primiti ve Solar-System Bodies -- Asteroids, Comets, and Meteorites, 1980-1990, Am. Nat. Acad. SCi.) develops the exploration goals for asteroids, and several NASA-advisory groups have studied potential asteroid missions. The French space agency has also fostered a mission concept, Asterex, for the European Space Agency (Brahic et al., 1979, Icarus 40, 423). There is also some interest in missions to some Earth-approaching bodies. Ground-based observing programs will remain the basis for asteroid research for same time, however, during the past three years several observing

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techniques have been newly applied to asteroids, with important results, including radar and speckle interferometry studies of main-belt asteroids. The latter technique seems to reveal asteroid satellites in several instances. After decades of ineffectual attempts to measure asteroid dimensions by stellar occulation, the last few years have seen an unprecedented number of successful observing campaigns. Another observing program that was progressing slowly during its early years but has proven very important recently is the Palomar Schmidt camera photographic search for Earth-approaching asteriods. A new project, designed to greatly increase the discovery rate, is under development: the spacewatch camera. It is a large asteroid telescope to be built on Kitt Peak which will employ a CCD-based, automatic scanning system to detect rapidly moving asteroids. Some IUE satellite data on asteroids have been published (cf. Butterworth et al., Nature 287, 701-703, 1980), and plans are moving ahead to analyze-asteroid data expected to be obtained by the IRAS satellite (see "proceedings" of Asilomar Conference, April 1980, in press). In most cases, the cited papers merely exemplify the kind of papers that have been published. While asteroids dynamics are not the responsibility of Commission 15, dynamical processes are inseparable from our topic, particularly in connection with collisional evolution and the origin of asteroids. Therefore, a very abbreviated discussion of some of the more relevant dynamical papers appears toward the end. Size, Albedos, Shapes, Masses, Configurations The largest asteroids produce measurable perturbations of the orbits of a few other bodies permitting masses to be measured. Schubart & Matson (Asteroids, 84-97) summarize the latest measu~~ments of Ceres, Pallas, and vesta, yielding densities of about 2 1/2 g cm for t~n first two and 3 1/2 for Vesta. All asteroids together total about 3 X 10 g. Diameters for over 200 asteroids determined by radiometry are tabulated in TRIAD by Morrison and are discussed by Morrison and Lebofsky (Asteroids, 184-205). Brown et al. (BAAS 13, 716-717, 1981) have recently recalibrated the scale, reducing diameters by about 5%, well within the previously reported systematic uncertainties. Lebofsky, Lebofsky & Rieke (AJ 84, 885, 1979) have studied small, Earth-approaching asteroids using the radiometric technique; they believe the radiometric model applicable to large asteroids may not be appropriate for many of the smaller asteroids, probably because the latter lack significant surficial regoliths. A detailed radiometric study of Eros was made by Lebofsky and Rieke (Icarus 40, 297, 1979). The potential asteroid-mission-target 1943 Anteros haS-been studied by Veeder et al. (Icarus 46, 281, 1981). Since the tabulation of TRIAD, many additional radiometric observations have been made by Gradie, Tedesco & their collaborators, especially of family members and other belt asteroids. They report that small Nysa family members are very dark, contrary to expectation. Attempts to test and calibrate the radiometric scale by direct measurement techniques have finally proven successful. Measurements for Pallas during the stellar occulation of 29 May 1978, yielding a mean diameter of 538 + 12 km (Wasserman et al., AJ 84, 259, 1979). Subsequent successful observations of occultations by 18 Melpomene, 3 Juno (Reitsema et al., AJ 86, 121,1981; Millis et al., AJ 86,306,1981), and other asteroids are sum-marized by Millis and Elliot (Asteroids, 98-118) and by Maley (JRAS Can 74, 327, 1980). General stellar occulation studies are reviewed by Elliot (Ann Rev AA 17, 445, 1979). Al though much less precise, diameter measurements compatible with the radiometric scale have also been obtained by speckly interferometry (Worden, Asteroids, 119; Worden & Stein, AJ 84, 140,1979).

COMETS, MINOR PLANETS AND METEORITES

A surprlslng outgrowth of the occultation observations has been the recognition that some asteroids may be double or have one or more smaller satellites (sometimes confusingly termed "minor satellites"). Reliable confirmation of such a satellite has been difficult to achieve. Possible examples are discussed by Van Flandern, Tedesco, & Binzel, Asteriods, 443. An August 1981 occultation may have provided the first photoelectric confirmation of an asteroidal satellite (of Melpomene), but the data are not completely reduced at this writing. The Occultation Newsletter provides continuing reports on this phase of asteroid research. Numerous unconfirmed visual reports of secondary occultations led Binzel and Van Flandern (Science 203, 903, 1979) to assert that retinues of minor satellites were the rule rather than the exception. Most experts are skeptical of this conclusion, but there is growing support for the view that some asteroids have companions. Speckle interferometry of both Pallas and Victoria suggest the presence of satellites (Hege et al., BAAS 12, 662, 1980); new work by Bowell et al. (BAAS 13, 719, 1981) is not inconsistent with the same conclusion. A possible photographic detection of a satellite for 9 Metis is reported by Wang et al. (Icarus 46, 285, 1981). Furthermore, some asteroid lightcurves resemble those of eclipsing binary stars (Tedesco, Science 203, 905,1979). Lightcurve studies have led to tentative conclusions regarding other unusual shapes and configurations for some asteroids. Hartmann and Cruskshank (Science 207, 976, 1980) have suggested a peanut-shaped model for the large Trojan asteroid 624 Hektor. Weidenschilling (Icarus 44, 807, 1980) suggests instead an equilibrium contact-binary model, and poutanen et al. (BAAS 13, 725, 1981) a biaxial model. Peculiar shapes of several asteriods, especially some rapidly rotating ones, are discussed also by Zappala (Moon Planets 23, 345, 1980) and Tholen (S & T 60, 203, 1980). Statistics concerning asteroid shapes are reviewed by Burns and Tedesco (Asteroids, 494) and Bowell and Lumme (Asteroids, 132). Lightcurves and Spins Extensive observing programs in Europe, California, and elsewhere have led to a remarkable increase in the number of asteroids for which information is available about rotation. While most asteroids rotate in about a third of a day, a few rotate as rapidly as every two or three hours, and a few hardly spin at all, with periods of many days. There have been several recent attempts to study the statistics of spins (Burns & Tedesco, Asteroids, 494; Harris & Burns, Icarus 40 115, 1979; Tedesco & Zappala, Icarus 43 33, 1980; Dermott & Murray, Natur~ in press 1981). The following trends-Sre apparently real, although not obvious, in the data: Asteroids larger than about 200 km are comparatively fast rotators. The very samllest asteroids are often fast rotators. At any specific diameter, main-belt, non-family asterorids of the C-type rotate sane what slower than S-type, which in turn rotate slower than non-(C,S,) types (see below for discussion of taxonomic types). M-types are often very rapid rotators. Members of major Hirayama families may rotate somewhat faster than average. Papers reporting high-quality lightcurves for one or a few asteroids are exemplified by the following: Dunlap and Taylor, AJ 84 269, 1979 (reports a 74h rotation period for 887 Alinda); Scaltriti, Zappala & Schober, Icarus 37 133, 1979 (several more long-period asteroids); Zappala, van houten-Groeneveld & Van Houten, A&A Suppl Ser 35, 213, 1979 (rapid spins for asteroids 349 and 354); Debehogne & Zappala, A&A Suppl Ser 40 257, 1980 (rapid spin for 45 Eugenia); Schober et al., A&A 91 1, 1980 (lightcurves for large asteroids 31 and 65); Tedesco and Sather, A~86 1153, 1981 (lightcurves for 29 ~nphitrite

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with up to 5 maxima); and Lagerkvist and Rickman, Moon Planets 24 437, 1981 (very rapid spin for 201 Penelope and M-Types). Largerkvist (Acta Astron 28 617, 1978) has summarized photographic lightcurve data for over 100 asteroids based on the program at Uppsala. harris and young (1980 Icarus 43 20· 1981, BAAS, 11, 744) summarize photoelectric data for many asteroids; they forsake high precision photometry and high time resolution in order to determine periods for the largest possible number of asteroids. Lightc urves also prov ide information on asteroid shapes and configurations and on spin axis orientations (cf. Taylor, Asteroids, 480. A new observing program has been started by Davis et al. (BAAS 13,725, 1981), directed specifically toward large, rapidly-spinning bodies that may have equilibrium figures; it may yield improved knowledge of axis orientations. Research on lightcurves is treated regularly in the Minor Planet Bulletin of the Association of Lunar and Planetary Observers. ----- -----Photometry, Polarimetry, Radar:

Surface properties

Radar observations of four Earth-approaching asteroids were swrunarized by Pettengill and Jurgens (Asteroids, 206). Ceres and vesta were the first main-belt asteroids to be detected by radar (Ostro et al., Icarus 40 355, 1979; Ostro et al., Icarus 43 169, 1980). More recently, Ostro, e~al. (BAAS 13 716, 1981) reported radar-detections of several more main-belt asterOids, including 16 psyche. It has the highest radar reflectivity found yet for an asteroid, which suggests that it contains much metal although probably not a pure-metal composition. Asteroids generally exhibit rather low radar reflectivities as well as large-scale roughness consistent with the presence of regoliths and irregular surfaces and shapes. Passive radio observations of several large asteroids (Dickel, Asteroids, 212) are also consistent with regoliths, as are infrared radiometric data. Optical photometry is sensitive to surface texture and properties in the uppermost millimeter of an asteroid's surface. All asteroids, big and small, exhibit photometric functions and polarization properties consistent with the presence of considerable surficial dust. Polarization measured as a function of phase angle is sensitive to albedo and grain opacities; recent work is reviewed by Dollfus and Zellner (AsterOids, 170); also Dollfus, Mandeville & Duseauz, Icarus 37 124, 1979, who discuss polarization of M-types and LeBertre & Zellner, Icarus43, 172, 1980), who treat vesta. Optical phase curves have been discussed by Bowell and Lumme (Asteroids, 132; also two manuscripts in press) who have developed a new scattering model. They show that albedos can be derived from such data. Lupishko et al. (Pis'ma Ast Zh 6, 184, 1980) discuss the opposition effect observed for 16 psyche and implications for its possible metal-rich composition. Polarimetric data have demonstrated the most asteroids are exceptionally uniform in albedo. Except for vesta (cf. Blanco & Catalano, Icarus 40 359, 1979) and a few other rather large asteroids, most asteroids also display uniform colors as they rotate (Degewij, Tedesco & Zellner, Icarus 40 364, 1979; (see also Bowell and Lurnme, AsterOids, 132). The uniformitymay reflect underlying compositional homogeniety or may reflect global blanketing by ejecta from comparatively recent, individual, large craters. The minor variations that do exist have been studied by Gaffey (BAAS 1],711, 1981). Colorimetry, Taxonomy, and Bias-Corrected Distributions A major problem that has been addressed over the past 8 years is asteroid

COMETS, MINOR PLANETS AND METEORITES

"taxonomy" (the classification of representative samples of asteroids, primarily by spectra and albedo properties) and studies of the distributions and correlations of the taxonomic types with other pysical parameters, including orbital elements. The taxonomic types used in the TRIAD file were defined by Bowell et al. (Icarus 35,313, 1978). Zellner (Asteroids, 783) has performed the bias-corrections an~puublished the definitive analyses of the distributions of those types. Briefly, the C-types are very dark and have neutral colors; S-types are reddish (often with absorption bands) and have moderate albedos; M-types are slightly reddened and have low to moderate albedos; E-types are neutral in color but highly reflective; R-types are very red and reflective, often with deep absorption bands; and U-types refers to all other asteroids that can't be classified C, S, M, E, or R. (Note an error in Zellner'S Table II: the lower limit for the BEND parameter for M should be 0.06, not 0.0). Zellner reports that size-distributions, analyzed separately for the different types and different zones of the asteroid belt separated by major Kirkwood gaps, vary substantially with type and solar distance and generally are not linear in log-log plots. Since publication of the Asteroids book, a major-new 8-color observing program has been performed by Zellner, Tdesco & Tholen (Zellner et al., BAAS 13, 171, 1981; Tedesco et al., BAAS 13, 712, 1981). Supplementary radiometry by those observers and Gradie haS-greatly extended the taxonomic data base. A preliminary taxonomic classification and bias-correction has been performed by Gradie and Tedesco (Science, submitted 1981; also see Tedesco & Gradie, BAAS 13, 718, 1981). Two new types have been defined: a very low-albedo, very reddish type (D-type, called RD by Degewij & van Houten (Asteroids, 417), and a very low-albedo, slightly reddish type (P-type). Gradie & Tedesco document a remarkable progression in asteroid types from inside the main belt to the vicinity of Jupiter. There are" rings", of typical width (1/3)a (where a is the semi-major axis of the middle of the zone), dominated by-a particular type. There is a progression from types E and R inside 2.2 AU, to S in the inner half of the main belt, to M in the middle of the belt, to C in the outer half of the belt, to P beyond the 2:1 Jupiter commennsurability (chiefly Hildas), to D which dominates among the Trojans. There are hints that the zone boundaries may correlate with major Jupiter commensurabilities. Zellner, Gradie & Tedesco have been tempted to ascribe the ordered progression of types away from the sun to a tableau of solar nebular condensates. But processes that could implant asteroids (from the inner solar system, for example) into the asteroid belt (cf. Wasson & Wetherill, Asteroids, 926) are controlled by resonances. In either case there is strong presumptive evidence that the variation in asteroid composition (as reflected by the types) with distance from the sun reflects a primordial feature of the population and is not due to currently operating processes. The above distribution studies have genenrally omitted the large Hirayama families on the supposition that they are fragments of a large disrupted asteroid. Analysis of the type distributions among family members (Gradie, Chapman & Williams, Asteroids, 359) sheds light on the nature of the precursor bodies. In general, the large families have fairly homogeneous compositions, but a large fraction of the less-populated families defined by Williams (Asteroids, 1040) are of heterogeneous composition. The family members cannot readily be "put back together again" in a way that makes geochemical sense. A recent surprising result that has emerged from the 8-color program and associated radiometry is that the small neutral-to slightly-bluish-colored members of the Nysa family are not E types (as is neutral-colored Nysa itself) but are very dark.

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Spectrophotometry, Compositions, Relations to Meteorites Visible and near-IR spectrophotometry, generally in 24 fil ters, has been published for 277 asteroids By Chapman & Gaffey (Asteroids, 655). Unlike the 8-color data, these spectra have sufficient spectral resolution (except for noisy spectra) to permit serious interpretation in terms of mineralogy. McFadden (BAAS 13, 718, 1981) has measured spectra of some small Earthapproachers. potentially diagnostic absorptions exist for several important minerals in the near-UV and near-IR. More features exist in the region beyond 1.1,liIm out to 4,Ll m where thermal radiation begins to mask reflection features. In particular there are features due to OH and organics near 3j.J. m. However, due to detector insensitivity, less than 20 of the brighter asteroids have been measured (generally 0.9 to 2.5jlm) by wedge-filter and interferometric techniques (reviewed by Larson & Veeder, Asteroids 724; also Feierberg et al., Geochim Cosmochim Acta 44 513, 1980; Gaffey & McCord, Asteroids, 688; Feierberg, Larson & Chapman, Ap. J. in press 1981). Many asteroids have been studied by JHK photometry (Larson & Veeder, Asteroids, 724) and by filter and CVF photometry near 3,Ltm (Lebofsky, AJ 85 573, 1980; Cruikshank & Howell, BAAS 13 717, 1981). Detailed filter and interferometric studies have been made of the 3~m regions of Cere's spectrum (Lebofsky et al., BAAS jl, 718, 1981 and longer manuscript submitted). Interpretations of spectral reflectance data in terms of mineralogy continue to suggest a relatinship to common meteorite types in the case of most main-belt taxonomic types, although absolutely firm identifications are usually not possible. Gaffey & McCord (Asteroids, 688 interpret C-type spectra in terms of carbonaceous chondrite-like assemblages, but important differences exist in some cases. Ceres and some other C-types show a prominent 3)Am water absorption due to hydrated silicates (just as in CM-types carbonaceous chondrites), and possibly even frost in the case of Ceres, (see Lebofsky refs. in above paragraph). Feirgerg et al. (Ap. J. in press 1981) find that most S-types are consistent with ordinary chondritic assemblages. They rule out stony-iron compositions, like those represented by stony-iron meteorites, among the larger, well-observed S-types, but cannot rule out collisionally jumbled differentiated compositions in many cases. Gaffey (BAAS 13, 717, 1981), However, believes that IR pyroxene band positions rule out ordinary chondri tic compositions for several S-types. There has been agreement on the basaltic composition of vesta's surface but disagreement concerning a diagnostic composition for 349 Dembowska (Champman, Asteroids, 25; Feierberg et al., Geochimica loc cit; Gaffey & McCord, Asteroids, 688. Outer-belt and Jupiter-region~pes (D and p) apparently are not represented among meteorites, but Gradie & Veverka (Nature 283 840, 1980) suggest kerogen-like organics. --Collisional Evolution of Asteroids It is clear that the dominant process affecting the physical properties of asteroids during most of solar system history has been their collisional evolution and processes of regolith formation. Although collisional evolution has been a subject of theoretical conjecture of three decades, the last few years have broght the topic to a new level of sophistication. Major new evidence from laboratory experiments in cratering and catastrophic fragmentation (e.g. Fujiwara, Icarus 41 356, 1980) and from meteoritics (e.g. Bogard Asteroids 558; Wood Asteroids 849 have been combined with new observational data on families, rotations, and asterodial satellites to yield a consistent -- though unproved -- model of asteroidal evolution. Major collisions among asteroids result in catastrophic fragmentation and, if fragements exceed escape velocity, disruption. Especially for larger

COMETS, MINOR PLANETS AND METEORITES

target asteroids, fragments may reaccumulate thus "jumbling" them and forming "megaregol i ths" • Dav is et al. (Asteroids 528) characteri ze fragmentation/disruption/reaccumulation-scenarios and calculate the evolution of asteroidal size distributions. A typical body larger than 30 km diameter survives disruption for about the age of the solar system but is likely to have been jumbled one or more times. Petrological studies of meteorites support the inferred re-accumulation processes (Rubin, Taylor, Scott and Keil, abstract for Nov. 1981 Houston workshop on Comparisons Between Lunar Breccias and Soils and Their Meteoritic Analogs). Collisional disruption presumably forms Hirayama families cf. Ko zai, (Ann. Tokyo Astron. Obs. II 11. 194, 1979). Collisions also probably determine asteroid spins, although there is hope that some subset of asteroids may largely retain primordial spins that could shed light on formative processes. Theoretical studies of the evolution of asterodial spins are summarized by Davis et al (Asteroids, 528; see also Ip, Icarus 40, 418, 1979; Harris, Icarus 40, 145:-1979). Recently there has been appreciation of the role of off-center-collisions and asymmetric ejecta escape (Burns and Dobrovolskis, BAAS 13, 719, 1981); these considerations may explain the observed tendency for smaller asteroids to spin slower than large ones, contrary to earlier expectations. Collisional spin-up especially of larger asteroids, combined with the megaregolith/re-accumulation models of Davis et al., may yield quasiequilibrium shapes and explain why few asteroids-Spin faster than 4 hours (Weidenshilling, Icarus 46, 124, 1981; Farinella et al., Icarus 46, 114, 1981). Weidenschilling and his colleagues show the bulk densities may be inferred for asteroids if they are, in fact, equilibrium figures. When additional angular momentum is delivered by collisions beyond the limits of stable single-body Jacoby ellipsoid figures, splitting into binaries may result. Chapman, et al. (BAAS 12, 662, 1980)suggest that a few percent of asteroids may evolve into binarY-configurations through collisional evolution. Several researchers have studied processes of cratering and regolith formation of asteroids (Housen et al., Icarus 39, 317, 1979; Cintala, head, & Veverka, Proc. 9th Lun. Planet.·Sci. Conf. 380~ 1981; and Langevin, thesis, Univ. de Paris-Sud, 1978, and several later abstracts by Langevin and colleagues in Lun. Planet. Sci. Conferences). The topic is reviewed by Housen et a1. (Asteroids 601) and updated by Housen (thesis, Univ. Ariz., 1981). Moderate to large asteroids generate up to 2 kilometers of surficial regolith prior to any catastrophic fragmentation events that may jumble moderate-sized asteroids. Asteroids smaller than 10 km diameter are expected to have negligible regoliths. The predicted characteristics of asterodial regoliths (more blanketing, less reworking, shorter exposure to solar wind, less agglutinate formation, coarser texture) are all qualitatively consistent with observed differences between lunar and meteoritic breccias although quantitative comparisons are not yet final. Earth-approaching Asteroids, Derivation of meteorites, Relationships with comets The Palomar planet-crossing survey has been described by Helin and Shoemaker (Icarus 40, 321, 1979) and by Shoemaker et al. (Asteroids 253). Down to about 1 km~iameter, it is expected that there are.~100 Atens (a < 1 AU), 700 ~ 300 Apollos, 1000-2000 Amors, 10000~ 5000 Mars-crossers, and-about 5000 Mars-grazers. As new discoveries are made each year by Helin and colleagues, these estimates are improved. Shoemaker finds these estimates to be consistent with the terrestrial and lunar cratering record, although he

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bel ieves live comets may be significant addi tonal component to the cratering flux. Wetherill (Icarus 37 96, 1979; also Sci. Am. 240 (3) 38, 1979) has discussed the Apollo/Amor population and concludes~at a supply rate of 15 objects per million years (larger than 1 krn diameter) is necessary to maintain a steady-state. The dynamical interrelations between comets and asteroids is discussed by Kresak (Asteroids 289; also Moon Planets 22, 83, 1980). Chapman & Greenberg (abstract 12th Lun. Planet. Sci. Conf.; also submitted to Nature 1981) have considered the collisional and cratering processes that might liberate meteorites from main-belt asteroids and deliver them to Earth-crossing orbits by dynamical mechanisms reviewed by Wasson & Wetherill (Asteroids 926). They believe that the principal traits of the terrestrial sample of meteorites can be understood by relying prrimarily on cratering impacts on large asteroids to supply most meteorites. An al ternate view (Wetherill loc cit) is that many meteorites are pieces of small Apollos. Chapman & Greenberg also treat the geophysical evolution of asteroids as meteorite parent bodies. They believe that just a few percent of the asteroids melted, presumably by one or more of the processes reviewed by Sonett & Reynolds (Asteroids 822). Subsequent regolith formation provided sufficient insulation to explain measured metallic meteorite cooling rates as occurring in bodies three times smaller than previously calculated (see also Wood, Asteroids 849). Metal-rich meteorites are derived from asteroids only 10 to 40 krn in diameter that are the cores of the smaller differentiated bodies, which have been stripped of their mantles by catastrophic fragmentation and disruption. An alternate view of iron meteorites being derived from incompletely differentiated or second-stage parent bodies is discussed by Scott (Asteroids 892). Gaffey & Lazarewicz (submitted to Icarus 1980) have also studied the thermal evolution of asteroids, and have considered, in particular, zonal metamorphism and resulting mineralogical compositions. Relationships between asteroids and meteorites are reviewed by Wilkening (Asteroids 61-74). Origin and Dynamical Evolution of Asteroids There is wide agreement that the asteroids represent the remains of material that failed to accrete into a full-size planet in the asteroidal zone, probably due to indirect effects of Jupiter. (The alternate view of van Flandern, Icarus 36 51, 1978, taht asteroids and comets are remnants of a former planet has-received little support). The early history of the asteroids is still not understood, of course, but there has been some convergence in thinking during the last several years. papers by Davis et al., Chapman, Safronov, and Cameron in Asteroids all rely on the gravitational perturbations by large planet-sized bodies temporarily crossing the asteroid zone in elliptical orbits to explain the enhancement of eccentricities and incliniations of asteroids that presumably contributed to the failure of asteroids to accrete (collisions tend to result in discruption at 5 krn sec ). Presumably a swarm of projectiles accompanying the largest Jupiterscattered body could have depleted the asteroids by high-velocity collisional destruction (Safronov loc cit.). The importance of self-collisions in removing mass from the-a5teroid zone is not clear, depending on the original size distribution. If it was very steep (such as derived by planetesimal modelling of Greenberg et al., Icarus 35, 1978) then much mass could have been lost. Few asteroids approaching the size of Ceres would have been disrupted (Davis et a1. loc cit.).

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COMETS, MINOR PLANETS AND METEORITES

Commensurabilities and resonances, due chiefly to Jupiter, have also been invoked to explain how asteroid velocities were pumped up (Torbett & Smolouchowski, Icarus 44, 722, 1980; BAAS 13, 719, 1981; Ward, submitted to Icarus 1981). The idea-is that Jupiter resonances swept through the asteroidal zone during the period of solar system formation. The existing Kirkwood gaps reflect the effects of the resonances on the now-stable system (Greenberg & Scholl, Asteroids 310; Zhuravlev, Astron. Ah. 57, 1056, 1980). More problematical is the manner in which the regions between the Cybele group and the Trojans have been cleared; the truncation of the asteroid belt has been studied by Franklin et al. (Icarus 42 271, 1980). V.

Interrelations Between Comets, Minor Planets, and Meteorites G. W. Wetherill

Almost all comets newly arr~v~ng from the aort cloud are ejected from the solar system by planetary perturbations after only a few perihelion passages (Weissman Comets 1982). Either this same ultimate fate or physical disintegraton befalls the small fraction of the new comets captured into short period orbits. In contrast almost all minor planets are in orbits that are strictly confined to the asteroid belt. Therefore, except for possible mixing under the changing physical conditions that existed during the earliest history of the solar system (1979, pollack et al. Icarus 37, 587; 1979, Wasson and Wetherill, 1979 Asteroids, 926), for the most part, from both the dynamical and compositional points of view, comets and asteroids constitute two distinct populations. However, the few possible exceptions to this rule, the planet-crossing asteroids (particularly the Apollo-Amor objects) should not be thought of as minor curios'ities, inasmuch as they are prime candidates for meteorite sources and terrestrial planet crater-forming projectiles. The question of whether some small fraction of the periodic comets evolve into devolatilized Apollo-Amor objects is discussed by Kresak (1979, Asteroids, 289); Degewij and Tedesco (1982, Comets); and Froeschle and Rickman (1980, A&A 82, 183). From the dynamic evidence, it appears likely that some significant-rraction of the Apollo-Amor objects are extinct cometary cores; possible "dormancy" of comets is also supported by evidence for inactive regions of Swift-Tuttle (1981, Sekanina, Astron. J.) by observations of Comet Bowell 1980b (1981, Sekanina, Astron. J.), and by the recent derivation of the Geminid stream from an object in an Apollo-like orbit. Spectrophotometric data, on the other hand, indicate no obvious differences between Apollo-Amor and main belt asteroids (1981, McFadden, BAAS). At least superficial similarities are found between distant asteroids and cometary reflectance spectra (1981, Tholen et al. BAAS) but uncertainty regarding whether or not the bare comet nucleus is actually being observed obscures the interpretation of this important result. The alternative of deriving Apollo-Amors from the main belt is described by Simonenko (1978, Meteorites - Fragments of Asteroids', Nauka Moscow) and Wetherill and Williams (1979, origin and Distribution of the Elements, L. Ahrens, ed. p. 19, Pergamon oxford). New calculations of the positions of the secular resonance surfaces, of great importance for the dynamical evolution of asteroidal fragments, are given by Williams and Faulkner (1981, Icarus). Cosmic ray exposure age distribution (1981, Crabb and Schultz, Geochim. Cosmochim. Acta) preclude obtaining any significant fraction of the meteorites directly from active comets; if there are cometary meteorites in our collections they are from extinct comets, probably Apollo-Amors of asteroidal appearance. Some evidence doess exist, however, for large meteors in cometary orbits with physical characteristics that may permit survival during passage

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through the earth's atmosphere (Wetherill and ReVelle, 1982 "Cornets"). Some weaker carbonaceous meteorites (CI and CM) may be cometary objects of this kind. Data supporting an asteroidal origin for these meteorites has also been presented (Kerridge and Bunch, 1979, Asteroids, 743). Evidence is accumulating for an asteroidal origin of most meteorites, even though important dynamical problems remain unsolved (Wasson and Wetherill, 1979, Asteroids, 926) and identification of particular meteorite types with specific spectrophotometric classes of asteroids remains uncertain (Chapman, 1979, Asteroids, 25). An asteroidal origin for the differentiated meteorites (achondrites, stony-irons, and irons) is rarely questioned. A strong case for derivation of a major fraction of the basaltic meteorites, the eucrites, from 4 vesta is provided by combination of spectrophotometric data (Feierberg and Drake, 1980, Science 209, 805) and petrological arguments (Drake, 1979, Asteroids, 765). Hostetler-and Drake (1978, Geochim. et Cosmochim. Acta 42, 517) propose that an Apollo-size ( 1 km) fragment of Vesta was deflected by successive collisions and gravitational perturbations into an unstable orbit, thereby overcoming dynamical problems associated with the fact that Vesta is not close to a secular resonance or commensurability resonance. Derivation of all asteroidal meteorites from such a hierarchy of intermediate size bodies is very likely (Turner, 1979, 10th Lunar and Planetary Science Conf. 1917); Wetherill, 1980, Meteoritics 15, 386). However, it is not clear why material from vesta should compete effectively with similar material from more conveniently situated asteroids from which much higher Earth-crossing yields shuold be expected. Discussions of other possible asteroidal sources of differentiated meteorites have been presented: S-asteroids (Wetherill and Williams, loco cit. 1979),346 Dembowska (Feierberg et al., 1979 Geochim. Cosmochim. Acta 44, 513), and inconsipicuous asteroidal cores as mesosiderite sources (Chapman and Greenberg, 1981, Lunar Science XII 129). The principal evidence for an asteroidal origin of the most abundant class of meteorites, the ordinary chondrites, comes from chemical and petrographic investigations of these meteorites themselves, particularly the gas-rich brecciated chondrites. Theoretical modeling of asteroidal surface evolution provides at least semi-quantitative support for associating these breccias with plausible asteroidal regoliths (Housen et al., 1979, Icarus 39, 317; Langevin and Maurette, 1981 Lunar Sci. XII, 602) as argued on the basis of solar and galactic particle bombardment phenomena by Anders, 1978 (NASA ConL publ. 2053, 57). In contrast, Goswami and Lal (1979, Icarus, 40, 510) and Heymann (1978, Meteoritics 13, 291) interpret similar data as indicating alternative origins for carbonaceous meteorite regoliths. An asteroidal origin of ordinary chondrites is also suggested by additional Ar- Ar evidence for relatively recent regolith formation (1980, Keil et al. Earth and Planetary Sci. Lett. 51, 235). If an asteroidal origin of chondrites is assumed, meteorite ana-fireball orbital evidence supports sources at least fairly deep in the asteroid belt, acceleration being achieved by interaction of commensurability and secular resonance (Simonenko loco cit. 1979, Levin, Zemlya Vselennaya no. 6, p. 5-9, 1980, Wetherill Meteoritics 16, 1981). Problems of identifying a sufficient number of ordinary chondrite sources spectrophotometrically still exist, but one interpretation of new IR data supports identification of the abundant S-asteroids with ordinary chondrites (Feierberg et al., 1980, BAASJ1, 664). Bertram Donn President of the Commission.

16.

PHYSICAL STUDY OF PLANETS AND SATELLITES (E~U-DE-PI[YSfQUE DE PLANETES ET SATELLITES)

PRESIDENT:

B A Smith

VICE-PRESIDENT:

V G Tejfel'

EXECUTIVE SECRETARY:

G E Hunt

ORGANIZING COWlITTEE: E Anders, J E Blamont, A Brahic, H S Bobrov, hT 11 Kaula, B J Levin, V I 11oroz, D llorrison, T COwen, G W Wetherill, A Wosczyk 1.

INTRODUCTIOn

The past triennium has seen an unprecidented increase in our knowledge and understanding of the solar system and, in particular, of the planets and satellites of the outer solar system. This epoch - 1 January 1979 to 31 Decenber 1981 - has witnessed major spacecraft missions to Venus, Jupiter and Saturn by the United States and the launch of further missions to Venus by the Soviet Union. In following the format used in the preceding Commission 16 report (1976-1979), it seems appropriate to simply review the highlights of the past three years and to provide a short list of comprehensive references, rather than to at tenpt the cus tonary abbreviated summary. Hos t of the wo rk ci ted has been published in ICARUS or in SPACE SCIENCE REVIEHS, which contain nost of the papers published in the field of planetary science in the English language. In an atterilpt to broaden the coverage, ho"ever, a review by V G Tejfel' of research carried out in the Soviet Union is included. Also included is a report by M E Davies on the IAU Joint \lorking Group on Cartographic Coordinates and Rotational Elenents of the Planets and Satellites. II.

SOLAR SYSTEM RESEARCH

The following suomary of accomplishments in planetary science over the past three years is necessarily incomple te. Hos t of the results which do appear are based on data obtained by American and Soviet spacecraft; nevertheless, any revie" of the current Ii t era tu re will underscore the inportance of groundbased telescopic observations and \lill emphasize the need to continue these useful observing prograos. a)

lIoon

A neu radar mapping of the l100n at 70cm \lavelength using the 430 Mhz radar at the Arecibo Observatory is being undertaken by T \I Thoopson. These new radar neasurenents Inll have better surface resolution (2-3km) and better radarrnetric control than the existing 70cm r:laps obtained in the late 1960's (T Thompson et al. Mocm Vol 9, 89-96, 1974). b)

11ercury

A comprehensive review, presented as a post-l1ariner 10 assessment of 11ercury, vJaS published by R G Stroo in Space Sci Rev 24, 3-70 (1979).

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Venus

Summaries of the results of the Pioneer-Venus mission have been published in Science 205, 41-121 (1979) and J Geophys Res 85, 7575-8337 (1980). These results include the composition and abundances of major, minor and noble gas species in the mixed lower atmosphere and the diffusely separated upper atmosphere. Isotopic ratios were determined for certain selected species. State properties of the atmosphere and the structure, particle size distribution, composition and optical properties of the clouds have been reported. Radar surface images and altimetry have indicated many tectonically-produced features and, when combined with gravity measurements, they indicate that the surface and interior of Venus is more like the earth than llars or the lloon.

Science 203, 743-808 (1979);

Analyses of Venera 9, 10 and 11 results have continued. Thermal radiometric studies have been published by L V Ksanfornality in Icarus 41, 36-64 (1980); the clouds of Venus have been discussed by H Ya llarov et al in Icarus 44, 608-639 (1930). A comprehensive review of the Venus atmosphere has been published by V I lloroz in Space Sci Rev 29, 3-127 (1931). d)

lIars

As of 31 December 1931, only the Viking 2 lander remains in operation, the two orbiters and the Viking 1 lander having ceased functioning during the reporting period. Analysis of Viking data has continued, however; an excellent summary of results appears inIcarus 45, 1-494 (1981). In Space Sci Rev 25 , 231-284 (1980), II H Carr has reviewed the morphology of the martian surface. e)

Outer Planets

The resul t s of the Pi one e r and Voyager missions to Jupiter and Saturn have been widely published. Voyager results for Jupiter are found in Scimce 204, 913-921 and 945-1008 (1979); Nature 280, 725-806 (1979); Science 206, 925-996 (1979);Icarus 44, 225-510 (1980) and J Geophys Res 8~ 8123-8841 (1981). Pioneer and Voyager results for Saturn are found in Science 207, 400-453 (1980) and Science 212, 159-243 (1931). An excellent summary of current knowledge of the Jovian s a t e l l i t e s will shortly be available in the book: SateZZites of Jupiter, edited by D l1orrison (Tucson: University of Arizona Press) 1982. A geological summary of the surface of 10 has been published by G G Schaber in Icarus 43, 302-333 (19UO). Hell infrared groundbased studies of the satellites of Saturn and Uranus have been reported by D P Cruikshank in Icarus 41, 246-258 (1980). A new treatment of the structure of the Uranus atmosphere has been presented by L ~Jallace in Icarus 43, 231-259 (19UO). The physics of planetary rings has been discussed by \HI Ip in Space Sci Rev 26,39-109 (1980). A meeting commemorating the 50th anniversary of the discovery of Pluto was held on 18 Fe brua ry 1930 in Las Cruces, Hew llexico, USA. A sunraary of current knowledge of this remote planet was discussed at the meeting and was subsequently published in Icarus 44, 1-71 (1980). Results include models for the structure and composition of Pluto by M J Lupo and J S Lewis and the positive detection of a methane atmosphere by U Fink et al.

PHYSICAL STUDY OF PLANETS AND SATELLITES

III.

a)

177

BRIEF REPORT 011 PLANETARY RESEARCH IN THE USSR (V G TEJFEL')

lIoon

A lunar globe at a scale of 1: 10 000 000 was constructed at the Sternberg State Astronooical Institute (l1oscow) and printed by "Nauka" Publishing House (llosco>l). Ne\J values of the oain photome tri c cons tan t s for the luna r surf ace \Jere derived for the true full moon. The monograph "Hodern selenography" was published by V V Shevchenko ("lJauka", lloscow). In the As t ronomical Council of the AcadeQy of Sciences (USSR), G A Lejkin, E V Zabalueva and L P Yaroslavskij have accomplished a granuloQetric analysis of the cooposition and structure of the lunar soil froo the "Luna-24" colur.m probe and have discovered multi-layered structure \nthin this probe. New maps of the color distribution on the visible lunar hemisphere Here constructed in the Kharkov University Astronomical Observatory (N N Evsyukov et al.). Nonlinear theory of the Hoon' s physical libration ~las developed in the Kazan University Astronomical Observatory. B Yu Levin (lloscoH) has showed that the Hoon must have a small core of melted iron, perhaps \vi th a moderate abundance of the iron sulfide. b)

l1ercury

The global regularities in the crater distributions on Hercury, }jars, and the Noon were studied by D A Kazioirov, J F Rodionova, B D Sitnikov et ale (Sternberg Astronomical Institute). A number of peculiarities in the distribution for craters with diameters more than 10 km was discovered. In particular it was noted that the density of the craters decreases from the poles to the equator on the Uoon and llercury, but increases from the north pole to south pole on tlars. c)

Venus

The spectral and temporal characteristics of the Venus clouds visible in ultraviolet Here studied by 0 H Starodubtzeva (Astronomical Observatory of the Kharkov University). It Has determined that the ultraviolet contrasts varied ,nth a period of 4.55 ± 0.05 days. d)

liars

The structure of two-dioensional autocorrelation functions for the Qesorelief of the oartian surface was studied by A 11 Grietskij (Astronomical Observatory of the Kharkov University). Yu V Aleksandrov and V P Tyshkovetz have obtained nelv estioates of dust particle sizes (about 20-25 1m) in the Qartian atoosphere during the great dust stroo of 1971. The cOQprehensive oonograph "Physics of the planet liars" by V I l1oroz (The Institute of Space Research of Acadeoy of Sciences, USSlt) was published in 1978 ("Nauka", lloscow). e)

Jupiter

During the 1979 apparition of Jupiter, the latitudinal and longitudinal variations of the color characteristics of the clouds were studied spectrophotometrically by V G Tejfel', G A Kharitonova, and G I Khudyaeva (Astrophysical Institute of Academy of Sciences KazSSR, Alma-Ata). They have showed that the correlation between color (spectrophotometric gradient) and the normal reflectivity of the cloud features on Jupiter is more cooplicated than a single-valued dependence. The spectral invariance of limb darkening for the polar regions of Jupiter at AA 0.33-0.70)lID was obtained from new spectrographic

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and spectrometric observations, consistent with the results from preceding years. This effect is connected with a presence of the high altitude aerosol layer over the Jovian polar regions. S t1 Gajsin (AII'1a-Ata) has obtained estimates of SOI'1e optical parameters of the cloud cover and overcloud atmosphere from observations in the near ultraviolet using a scanning spectrometer; V D Vdovichenko, with the same spectroI'1eter, has studied the brightness distribution on the Jovian disk along both the central neridian and the light 8nd dark belts within the near-IR I'1ethane absorption bands (fran 7250 to 9900 A). lIe has analyzed the results in terI'1S of a tHo-layer nodel of the absorption-band fornation. A new analysis of these bands in terns of a two-layer nodel also lIas carried out by L A Ilugaenko, L '1 Kislyuk and A V florozhel1ko in the l1ain AstronoI'1ical Observa tory of the Ukrainian Academy of Sciences (Kiev). New estimates of the Jovian spect ral reflectivity atAA 0.32-1.00\ln were obtained at Alna-Ata and Kiev. Polarinetric uaps of Jupiter were constructed by 0 R Bolkvadze at the Abastuman Astrophysical Observatory. f)

Saturn

o I Bu[;aenko and A V 110rozhenko (Kiev) have analyzed polarimetric neasurenents of Saturn and have interpreted the discovered peculiarities in the polarization properties of the equatorial region; these result from the occurence of oriented aerosol particles, which nay be injected into the Saturnian atmosphere from inner rings. New measurements of the brightness distribution on Saturn's disk and the limb darkening coefficients within the nethane absorption bands and the nearby continuum were accomplished by Z N Grigorieva, V G Tejfel', K S Kuratov, and G A Kharitonova (Alma-Ata) and A P Vidnachenko (Kiev). The structure of the methane absorption band at 6800 A in the Saturn spectrum lJaS analyzed by A A Atai (Shemakha) and V V Avramchuk (Kiev). !lore than 30 components of this band ,Jere detected. Variations of polarization with phase an[;le on Saturn's disk were studied by L A Sigua (AbastuI'1an Astrophysical Observatory). The nean radius of the cloud particles was estinated to be about 1 \lI'1 froI'1 this study. g)

Uranus

The knolJO data pertainin[; to the wavelength dependence of the geometric albedo of Uranus "ere analyzed in terms of SOI'1e models of atmospheric structure by A A Atai (Shemakha), K S Kuratov, V G Tejfel', and V D Vdovichenko (AII'1a-Ata). The best fit between the theoretical calculations and observed data was obtained for a I'1odel "ith an optically thick, pure gaseous atmosphere cOlabined with a Rayleigh scattering and optically thin aerosol haze layer over the tropopause. The methane abundance over this layer I'1ust be very low - about 240 ~~-aLlagat, and in the 101ler atI'1osphere the abundance ratio CH 4 /H 2 is about 3.10 (V G Tejfel'). h)

Satellites

The brightness and color variations of the Galilean sate IIi tes of Jupiter and the bright, icy satellites of Saturn versus orbital and solar phase angles Here measured by V V Avramchuk, L R Lisina, and V I Shavlovskij (Kiev). A F Steklov has analyzed a diurnal thenaal regime for the surfaces of the Galilean satellites, Triton and Pluto from theoretical considerations. G A Lejkin (lloscow) has noted that 7 of 9 known volcanic centers on 10 are lying near a great ci rcle Hhich nay be a [;10 bal crack on the sa telli te surf ace.

PHYSICAL STUDY OF PLANETS AND SATELLITES

i)

179

Pluto

v V Avramchuk and L R Lisina have neasured the geoQetric albedo of Pluto in the UIlV systeQ and have confirmed both the decrease of Pluto's brightness and the changes in color. 5.

JOINT lJORKIUG GROUP Oll CARTOGRAPHIC COORDINATES AND ROTATIONAL ELEllEUTS OF TIlE PLANETS AND SATELLITES (11 E Davies)

The Coramissions 4 and 16 Joint Horking Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites is updating its 1979 report. The principal source of new information has come from the Voyager encounters "'ith Jupiter and Saturn. Craters have been selected to define the longitude systeQs on the Jovian satellites Europa, Ganymede, and Callisto. For 10 the rate of volcanic resurfacing appears to be so high that a chosen landmark might not be recognized on pictures taken by future spacecraft, so the current (IAU, 1973) longitude definiton is retained. Suitable surface features "'ill be selected to define the longitude systems on the major Saturnian satellites (except Titan, "'hich is cloud covered). The system III (radio) rotation period and longitude systens are recomnended for use on Jupiter and Saturn. The current Qerabership of this comnittee is 11 E Davies, Chairman, V K Abalakin, J H Lieske, P K Seidelmann, A T Sinclair, Y S Tjuflin (consultant), A M Sinzi (ex officio), and Il A Smith (ex officio).

B A SMITH President of the Commission

19. ROTATION OF THE EARTH [ROTATION DE LA TERRE). President : P. Paquet Vice-President : Ya. S. Yatskiv Organizing Committee: B. Elsmore. H. Enslin. C. Kakuta. B. Kolaczek. W. Klepczynski, V. Naumov. E. Proverbio. E. Silverberg. R. Vicente. K. Yokoyama. Introduction During the period the activities of the Commission were expanded by several major events which have had beneficient effects on the determination of the Earth's rotation parameters [ERP): _ the People's Republic of China becoming member of IAU the astronomical observations were available for the international services or special experiments as MERIT. This contribution is more specially noticed in the reports of BIH and IPMS. - by the organization of the MERIT campaign the scientific communauty succeeded to set up a first world campaign with a simultaneous operation of all the techniques currently available : classical astronomy. Doppler. Laser and radio-astronomy. The analysis of such a set of data confirms the necessity to refine the relations between the reference systems associated intrinsically with each approach. - the increased accuracy obtained in the determination of the ERP and in geodynamics as well require a better definition of a conventional Reference System and its maintenance. To fulfill these objectives a new Working Group has been established by the IAU Colloquium 56. - the 1979 IAU Theory of Nutation has been revised in order to be in agreement with the resolution taken by IUGG in December 1979. A large majority [80% ) of Commission 19 was in favour of that modification and adopted the 1980 IAU theory of Nutation. On the other hand the difficulties to maintain in operation the classical instrumentation in some of the ILS stations seem to be in an irreversible status [refer to IPMS report)) but let us hope that. in a near future. periodic measurements will be possible with new techniques in all of the ILS stations. Changes in the instrumentation Lists of the instruments collaborating in international programmes are published in the Annual Reports of the BIH and IPMS. Borowiec: observations with a Danjon astrolabe started in 1981 while those conducted since 23 years with a transit instrument were terminated. CagZiari: three instruments are now in operation. a WANSCHAFF zenith telescope. a PZT in loan from Mizusawa. a Danjon astrolabe respectively since 1979.1980. 1981. The WANSCHAFF is working in parallel with the similar instrument of Carloforte. NataZ: the Universidade Federale do Rio Grande do Norte is installing a Danjon astrolabe transfered from Herstmonceux. BrusseZs, Mizusawa, Ottawa, San Fernando: new Doppler equipments TRANET II are installed or tests are in progress. Simeiz: has been equipped with a Doppler receiver MX-1502 in addition to the laser ranging technique and astrolabe. Potsdam: a new PZT. made by ZEISS [Jena) was brought into service in july 1980. The programme of observations is the same than for the old PZT.

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Research in instrumentation

Borowiec: a Doppler station which is expected to be in service in 1982 is in progress of installation. CagZiari: a laser system is in construction while a Doppler equipment is in test. Canada:-development of a geophysical Long Base Interferometry (LBI) system has been under way since 1978. Experimental results demonstrated viability of a commercial satellite communication link for operation of LBI with relative phase stability of about 2 x 10- 15 for a period of one day. It is planned to complete the LBI with near real time data processing by 1986. -Surveys and Mapping Branch reports, by Dr. A. VAMOSI, that a prototype of a microprocessor controlled portable Transit reoorder is experienced for geodetic purposes and development of a PZT. Transit are measured with a precision of 5 ~s on a star of magnitude 6. CERGA - Grasse: - a photoelectric astrolabe has been developped and operated. The first results show that the epoch at which a star cross the primary vertical is determined with an error of the order of 5 or 8 ms. The instrument will be used for UTD and also to continue the catalogue of absolute declination. Dresden: a system of electronic levels has been applied as a Horrebow level system at the transit instrument by Potthoff and Wachter (25.032.058; 27.031.530). Development of a photoelectric Circumzenithal is continued (27.031.531). Herstmonceux:- the control system of the PZT has been rebuilt. Some mechanicalwor~ has been done to counteract the effects of age and wear in the plateholder location and traverse systems. -a satellite laser ranging system is being built by RGO and the University of Hull. It is expected to be in regular operation, not only for ER, by late 1982. Mizusawa: a full automatic photoelectric astrolabe of Tsubokawa type is now in provisional observation. Potsdam: Major (1979) has experienced a photoelectric transit, investigations of a photoelectric recording of epochs of transit of stars are conducted with the aim to develop a PZT with a photoelectric detecting device (Meining et aI, 1979), (Nguyen Tri Long 1979 a, b, c), a new approach for the compensation of the axis of inclination of the transit instrument is proposed by Dittrich et al (1980). US NavaZ Observatory: - a visual 20 cm instrument (PZT6) is tested in Richmond and compared to the PZT2 the improvement is expected to be of the order of 10 to 20%. -a visual 65cm instrument (PZT7) has been in operation; the improvement in the internal precision over that of PZT3 is about 25%. -construction of a 20 cm instrument (PZT8) is nearly completed. USSR: research of instrumental'errors of classical astronomical techniques is being continued. Different methods of determination of the scale of ZT have been discussed in Pulkovo (27.032.004) and in Blagoveshchensk (27.032.024). Z.M. Malkin (27.032.023) considered the method of calculation of the scale of the PZT. The instrumental errors of PTI is studied by K.A. Steinset et al. (27.041.046,27.041. 050) and by M.I. Il'kiv et al (27.041.021). V.A. Naumov and Z.M. Malkin (27.044. 004) modernized the system of time registration of the Pulkovo PZT2. Revision of observing catalogues and of earlier observations G.M. Blank (25.044.013) considered the errors of the Catalogues of stars used by the USSR Time Service. A.A. Tochilina (27.044.015) discussed the determination of time with the Moscow PZT; V.A. Naumov et al. (27.041.018) and E. Ya. Prudnikova (27.045.011) undertake the second readjustment of observations with ZTL-180 for the years 1967-1974 and an analysis of latitude variations of Pulkovorespectively. In collaboration with the observatory of Mizusawa, D. Mc Carthy (1980) investigate a possible observing program for the PZT at 39° latitude Nord. J. Vondrak (1980a) determined the mean positions and proper motions of 304 stars observed during 1973-1 978 wi th the PZT of Ondrejov. The new posi tions were used to re-reduce all the PZT plates (Vondrak, 1980£).

ROTATION OF THE EARTH

183

Due to influence of precession, the programme of observations with the astrolabe of Potsdam has been modified (Hopfner, 1980b)while correction to the FK4 stars were deduced from the past observations (Hopfner, 1981a). On the basis of the 22 years of operation performed with the PZT of Hamburg an improved PZT catalogue is in preparation and could be ready for mid-1982. Earth's rotation from the new techniques The impact of the new techniques on the ER studies has been more sensitive during this period, mainly by the organization of the first MERIT campaign (see reports of BIH, IPMS, MERIT WG).

DoppZer The observatories of Belgium, Calgary, Mizusawa and Ottawa, by their continuous observations are contributing to the determination of the oMAHTC polar motion. In Ottawa special Doppler data reduction package has been developped to evaluate residual variation in station pOSitions, polar motion and UT1 (Kouba, 1981). At the observatoire Royal de Belgique the software has been improved (Paquet et aI, 1979) and compared to other methods of analysis (Boucher et aI, 1979). The time evolution of the station coordinates is given in Paquet (1980). The Groupe de Recherches de Geodesie Spatiale (France) managed the MEooC project of Doppler determinations of the polar motion, using Transit satellites, with the participation of the DMAHTC of several foreign organizations and of four french stations. In october 1980 the current operation was interrupted in order to prepare an improved MEDoC by the use of better receivers, model of forces and data transmission means. Laser The observatories of Cagliari and Herstmonceux are installing Satellite Laser Ranging (SLR) equipment while the station of Wettzell is in progress to run a Lunar Laser Ranging (LLR) station. Potsdam has managed a SLR station during the MERIT campaign (Montag et aI, 1981). The SLR station of CERGA is operational since 1979 and participates to LAGEoS and STARLETTE ranging. A cooperation between CNES, GRGS and the San Fernando Observatory (Spain) is established for the operation of the San Fernando laser station. Pole determinations from SLR data were performed by CNES and GRGS; researches continue on this topic, in cooperation with BIH. The first identified lunar laser returns from the CERGA LLR station were obtained in June 1981. The theoretical work and the interpretation of observed data from Mc Donald and orroral stations are pursued in CERGA, in the framework of ERoLD. In cooperation with the University of Texas, a new lunar ephemeris has been established, which was used for the evaluations of UT1 published by the BIH and for the MERIT short campaign. Radio-astronomy The Jet Propulsion Laboratory conducts two single baseline VLBI experiments per week using the 64 meters radio telescopes of the Deep Space Network. The results from these experiments are used for earth orientation estimates and to monitor station clock behavior and have made available to the BIH, starting in July 1980. (Fanselow et al, 1979; Fanselow, 1980, 1981). At the USNo, routine observations have been made continuously with the 35-km connected element radio interferometer (CERI) at Green Bank, West Virginia. Since only one baseline is available, two parameters analogous to the variation of astronomical latitude and UTo-UTC are routinely determined. Three days of observations are used to form one normal point which is transmitted to the Bureau International de I' Heure and the International Polar Motion Service. Preliminary analysis of the observational results shows that the connected-element interferometer may be expected to contribute an important ~art of future observational efforts.

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Reference systems for study of the Earth's rotation Taking into account the development of geodynamics and the relations existing between space geodesy and ER studies an IAU Colloquium (N° 56) on Reference Coordinate Systems for Earth Dynamics has been held in Warsaw in 1980. As a consequence the International Association of Geodesy and IAU Commissions 4, 19, 31 decided to create a joint Working Group having the task to prepare a proposal for the establishment and maintenance of a conventional terrestrial reference system. The WG is chaired by Prof. I. Mueller and the members are MM. E. Gaposchkin, B. Guinot, B. Kolaczek ,J. Kovalevsky, D.O. MCCarthy, N.G. Melbourne, P. Melchior, K. Yokoyama. A first meeting has been held in May 1981 (Grasse). E.P. Fedorov (1980)' Ya.S. Yatskiv and a1. (1980) discussed the definition and establishment of the basic coordinate systems in astronomy and geocynamics. Ya. S. Yatskiv (1980) reviewed the establishment of the terrestrial coordinate system by classical astronomical methods. M.M. Oagaev (25.044.004) considered the terminology in reference systems of time. P.L. Bender (1981) reviewed the use of new observational techniques to determine terrestrial reference frames which are suitable for investigating both worldwide tectonic plate motions and variations in the earth's rotation. The particular case of using laser range measurements to the Lageos satellite for this purpose was discussed earlier by Bender et al (1979). Research in problems concerned with the rotation of the earth

Theoretical studies

A.I. Rybakov and E.P. Kalinina (27.044.010) integrated numerically the differential equations of motion for the Earth-Moon-Sun system for the time span of 100 years. The value of the angular a~celeration of the Earth was estimated to be 0.66 x 10- 11 day-2. T.V. Ruzmaikina (27.081.063) considered the nonhydrostatic quadrupole excess moment of the Earth. V.N. Zharkov and S.M. Molodensky (27.081. 073) derived the Love numbers of the anelastic Earth. S.M. Molodensky (1981) considered the effect of ocean tide and anelasticity on the nutation. Theoretical calculations of the tidally induced variations of UTi have been presented in Yoder et al (1981 a, b). These calculations, which include contributions from the oceans and fluid core, have been compared with solutions for the coefficients of the monthly and semi-monthly terms using lunar laser ranging data. The observational and theoretical results agree within the errors. They also estimates other small periodic terms in ER and nutations due to geophysical effects. J. Wahr et al (1981a) analysed the effect of a fluid core on changes in the length of day due to long period tides. They conclude that the poorly understood decade fluctuations in the ER rate will prohibit observation of this effect (10ms at 18.6yr). Williams and Melbourne (1981) have examined the influence of the precession constant in the present system of definitions and coordinate systems and have concluded that a consistent, but imperfect, value of the precession constant will cause a linear drift between UTi values derived by classical optical techniques and the inertial techniques of lunar laser ranging and VLBI. It is recommended that the equation for Greenwich Mean Sidereal Time allows for future improvements in the precession constant. J. Vondrak et al (1982) derived the direct influence of Venus, Mars and Jupiter on the precession and nutation of the Earth's axis of rotation. T. Sasao et al (1981a) shown that diurnal atmospheric and oceanic loading of the Earth's surface provide an efficient mechanism for the free core nutation. Okamoto and Kikuchi (1981) clarified statistical properties of the Chandler wobble in the theoretical and finite discrete cases; The method of analysis of the Chandler wobble was shown with the statistical features of the excitation process taken into account. J. Wahr et al (1981 b) show that tides in the open ocean and the Earth's response to those tides are resonant at (1+1/460) cycle day~1J the effect on the Earth's nutational motion could be as large as 0.002 arcsec at 18.6 yr.

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Sato (1979) estimated the effect of annual parallax on the latitude variation using spectroscopic parallaxes of the ILS stars. The work for determining spectroscopic parallaxes of all time and latitude stars is still under way. The investigations of tidal friction in the present oceans and those of the geological past are presented in Brosche et al (1979, 1980) and Brosche (1979).

Decade ftuctuations

The "decade" fluctuations in the Earth's rotation were re-determined in the period 1861-1978 from an analysis of timings of occultations of stars by the Moon(26.044. 001). This analysis was extended back to 1600 and the resul ts were reported at IAU Colloquium N°S6. Secular changes in the Earth's rotation were investigated using ancient Babylonian timings of lunar eclipses.

Relations with geophysical phenomena

An extensive review of the relations between ER and Geophysical causes is given in the book of K. Lambeck (1980). Fluctuations in the atmospheric angular momentum were determined by the Meteorological Office, UK, and the National Center for Atmospheric Research, USA, from wind and pressure observations obtained in the Global Atmospheric Research Programme for the periods January-March and May-June 1979. These were found to correspond fairly well with equal and opposite changes in the Earth's solid mantle (28.044. 035). These results have shown the desirability of calculating the atmospheric angular momentum on a regular basis. N.S. Sidorenkov (25.044.001) investigated the role of the atmosphere in the excitation of long-term variations in UT1 using the meteorological data for the years 1956.8-1977.0. These variations are shown to be resulted from the mechanical influence of the atmosphere on the Earth's surface. He also proposed to use the information of the irregularities in UT1 as possible indices of global water exchange (27.044.034). In K. Lambeck et al (1981) the zonal angular momentum of the atmosphere has been evaluated and compared with astronomical observations for the period 1963 - 1973. Hara (1980) discussed the relation between the UT1 variations and the atmospheric excitations. He showed that mountain torque due to Hymalaya-Tibet plateau and the Rocky mountains are three times larger than surface stress. Oaillet (1981 a) analyses the excitation of the annual wobb Ie by the atmosphere. Jochmann (1981c) developped a model of polar motion and uses it to analyse the influences of the deterministic and stochastic parts of the meteorological excitation function on polar motion. On the basis of Schwiderski's oc~an tide models T. Sasao et al (1S81b) analysed the effects of ocean tides upon 5 ILS stations. The effect may reach several milliarcseconds at near-coast station. They recommend to correct the astronomical data for ocean tides. The relation between zonal tides and length of day are analysed in Merriam (1980). OJ urovic (1981) assumes that a correlation between some particular fluctuations of the ER and the solar activity are existing. Barlik et al (1980) are carrying on gravimetric measurements on the meridian of stations in Jozefoslaw in order to determine variations of meridian components of the vertical and find correlations with mean latitude variations (Kolaczek et a 1,1 980) • Melchior P., (1979)presents the experimental results deduced from Earth Tides observations and a discussion about the nutation tables. The influence of Earth tides on the modern techniques observing the ER is emphasized in Vicente (1979). A review paper giving an overall view of the researches concerning the structure of the Earth and the nutations is given in Vicente (1980). Also related to the Earth's structure a Working Group from IUGG, which intends to publish an international reference Earth model, has published a preliminary final report in Oziewonski et al (1981). S.M. Nakiboglu et al (1980) present the secular motion of the Earth's rotation pole as deduced from astronomical observations as a pos~ible consequence of the viscoelastic response of the Earth to the mean displacements caused by late Plei-

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stocene deglaciation and concomitant sea level changes. The Centre for Astronomy of Bucharest started studies on the relations between ER and internal structure of the Earth. Plate motions are also analysed from the latitude observations. At the Universidad Complutense of Madrid. Dr. Sevilla is establishing a group for theoretical works related to nutations. reference systems and ER.

AstponomicaZ pefpaction Sugawa and Naito (1981) showed that there exists a refraction anomaly of the order of 0~01 in the observed time and latitude with the time scale of about several ten minutes due to density variations caused by advections and internal gravity waves. VaPia

A. Stoyko (1980) prepared a first complement to the bibliography related to the astrolabes. Analysis of observational data

EaPth's potation paPameteps Routine predictions of polar motion and UT1-UTC were initiated during this time by USNO. The predictions are currently based on BIH Circular 0 and Rapid Service results. These values along with estimates of their accuracy are published weekly in the USNO Time Service Publications Series 7 and are available immediately to users equipped to access the Time Service HP 1000 computer. The rms accuracy of these values is expected to be better than ± 0~03 in polar motion and t oio07 in UT1-UTC forty days after predictions are made. The accuracy improves appropriately for dates less than forty days following the time of prediction. Klepczynski W. (1980). Klepczynski et al (1980). Mc Carthy et al (1979. 1980). An algorithm has been developped to treat observations made with new observational techniques as well as the classical methods. This procedure treats data obtained with any technique in the same manner to estimate the polar motion and UT1-UTC. Preliminary efforts have made use of optical. Doppler satellite. laser ranging to satellites and radio interferometer observations to determine the orientation of the Earth. It is anticipated that these results will also be available through the weekly Series 7 Publication and immediately accessible through the Time Service HP 1000 computer. Manabe (1981) developed a new algorithm for the reduction of PZT observations using the method of non-linear least-squares. Vondrak (1979) also prepared a new analysis of PZT observations. G.P. Pil'nik (25.044.009. 25.081.007. 27.044.014) considered the problem of derivation of the Love number k and nutation from time observations. Different determinations of the nutational coefficients from observational data have been finished to the IAU Symposium N°78 (27.043.008. 27.043.014). At the Observatoire de Paris the homogeneous series of latitude observations initiated in 1956 has been analysed to determine the nutation. some particular periodic terms (26.043.001. 26.044.007. 27.043.011. 27.043.012. 27.045.002. 27.045.033). the Earth tides coefficient A (Chollet 1980). The latitude observations performed at Potsdam between 1957.8 and 1977.0 were also analysed (Hopfner. 1979) to determine similar parameters than in Paris. The results of Potsdam were compared with those obtained in Paris and special investigations were carried aut to study the Chandler period. its variation and the half Chandler period (Hopfner. 198oa. 1981b. Jochmann (1980. 1981 a. 1981 h). D. OJ urovic (1979 a. b) identifies several periodic terms and the irregular fluctuations of the seasonal components in the series UT2-TAI covering 1967 to 1978. At the Jet Propulsion Laboratory. Pasadena. the rotational orientation of the earth (~UTO at McDonald Observatory) has been determined from lunar laser ranging (LLR) measurements for the interval 1971 to 1980. The results have been differenced from those obtained by conventional means as published by the Bureau

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International de I'Heure (BIH), on its 1979 system. The difference displays a quasi-seasonal signature, which the JPL group ascribes to systematic errors in the conventional measurements. Also, a comparison of polar motion results from three sources (Bureau International de I'Heure (BIH), Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC-Doppler), the International Polar Motion Service (IPMS)) was performed using lunar laser ranging (LLR)data. Results are given in H.F. Fliegel et al (1982) and J.D. Dickey et al (1982).

Latitude variations

S. Manabe et al (1979) have determined the declination corrections and the short periodic latitude variations derived from the recalculated past ILS observations. B. Kolaczek (1979), B. Kolaczek et al (1981) investigate the variation of mean latitude stations and their influence on the polodia. Large influence of mean latitude variations on polodia was found especially in the case of small number of stations like in ILS. Spectral analysis of modffilled latitude variations including sudden and continuous time variations was made in A. Brzezinski et al (1980). In order to study periodical terms of latitude variations B. Kolaczek (1980), Jacks (1981), Jacks et al (1979, 1980) perform spectral analysis of different set of latitude variations of individual stations as well as polar motion. Latitude observations were also analysed in Dresden (21.045.003).Polar motion, longitude and latitude variations are also analysed by Moczko (1980) and Schillak (1980).

AnnuaZ and ChandZer components

V.I. Sakharov et al (25.045.003, 25.045.004, 27.045.001) derived the variation of amplitudes and phases of the annual and Chandler terms from observations covering the period 1893-1974. Okamoto and Kikuchi (1981) found the 30-yr periodicity of the mean pole with amplitude of 0~034 in the direction of the 142°W - 38°E which is considered to be due to the non-polar variation of Ukiah station. Wu Shouxian et al (1979, 1981) give the results of their researches on the characteristic and the modulation of the Chandler component. An estimation of the Chandler period and the so-called 30yr period have been computed from the homogeneous ILS polar motion series in Wilson et al (1980). W.E. Carter (1981) suggests that the Chandlerian component may be frequency modulated as a linear function of the polar motion magnitude. Daillet (1981b) considers the correlation between the pole tide and the Chandler wobble ellipticity. Comments on the Chandler wobble Q are given in Merriam et al (1979). REPORT OF THE BUREAU INTERNATIONAL DE L'HEURE. This report covers the activities on the rotation of the Earth. The BIH work on atomic time is presented to Commission 31. During the last three years, the BIH has been increasingly involved in the new techniques for evaluating the Earth's Rotation Parameters (ERP). The year 1980 was especially marked by the BIH participation to the MERIT short campaign which had two aspects: a BIH participation to some techniques of measurement, and the coordination of the campaign. We will present first the research work, then the participation to MERIT, and finally the BIH current evaluation of the ERP which was drastically improved by the inclusion of new series of data.

Researches

The members of the BIH team participated to the researches on new techniques for measuring the ERP and to their implementation. Gambis participated to the Doppler project MEDOC (Gambis and Nouel, 1980), then evaluated the ERP from LAGEOS laser ranging in the framework of MERIT. Researches on SLR continue with the aim of improving the results, and of investigating the possibility of an observatory type operation: local filtering and data-compression, central reduction by an international body. The EROLD project entered an active phase, and BIH estimates

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of UT1 have been issued in cooperation with CERGA (Calame and Guinot. 1979: Calame. 1979. 1980. 1981). The theoretical aspects of the rotation of deformable models of the Earth are being considered by Capitaine (1980a). In particular this work clarified some problems concerning the corrections for diurnal nutation. Capitaine also participated to several studies on the effects of the Earth tides on the rotation of the Earth. Some determinations of nutation coefficients have been performed on the data of the Paris astrolabe (Capitaine. 1980b) and on the BIH results (Feissel and Guinot. 1980); further work on this topic is in progress in cooperation with a Chinese astronomer in stay at BIH for two years. The occurrence of short term irregularities of UT1 has long been suspected by BIH: mention of such events has been made in BIH circulars in 1968 and 1971. Feissel and Gambis (1980). using independent measurements of UT1. have confirmed these irregularities. which appear as series of waves with periods of the order of 50 days and a peak to peak amplitude of several milliseconds. These irregularities. as well as longer term variations are highly correlated with the angular momentum of the atmosphere: researches continue on this topic. in cooperation with meteorologists and geophysicists. As long as the ERP were referred to the plumb lines. the link between the space reference system and the geodetic coordinates was rather loose. But. with the development of methods which refer the ERP to the figure of the Earth. the definition of the systems of reference becomes critical in the BIH work (Capitaine and Feissel. 1981). The experience gained at the BIH allowed to propose statistical methods for defining the conventional terrestrial system of reference for the ERP and the geodetic coordinates (Guinot. 1981). In conjunction with considerations on the space reference system. the BIH participated to the redefinition of the Universal Time. when adopting the IAU (1976) System of Astronomical Constants.

Participation to MERIT

The BIH participated to the organization of the project through their membership in the MERIT steering committee. The BIH acted as computing centre in two of the techniques involved in the 1980 Short Campaign (optical astrometry and SLR). The BIH was designated as coordinating centre for the short MERIT campaign. To fulfil its duties. the BIH developed with the help of P. Morgan (National Mapping. Australia) a system of access to files in the GE mark III worldwide computer network. This system remained in use after the end of the campaign. Weekly and monthly status reports were issued during the campaign. The BIH prepared the supplement to the Short Campaign Report which contains informations on the observations and the 25 different series of ERP that were computed by the Analysis Centres. Other duties were the comparison of the series of measurements and. if possible. the evaluation of the ERP from a combination of r3sults. These tasks are. in fact. the continuation of the efforts undertaken at BIH for using currently the data of new techniques. These matters will be considered in the ne~t section.

Current evaluation of the ERP

Fig. 1 shows the relative weights of the techniques used in the current 5day evaluations of the coordinates of the pole and the square root of their pair variance 0(2.5 days). This latter quantity is believed to represent the measurement uncertainties. The local deterioration in 1979 is due partly to the decreasing quality of the optical astrometry prior to the availability of the chinese observations and partly to the unusual irregularities in the Doppler solution: four different satellites were used during the year. Concerning UT1. the optical astrometry (85% in 1981) and the connected element interferometry (CERI. 15% in 1981) are the only contributors. The pair variance of UT1 is of little significance on account of the noise of UT1 itself. Fig.2 shows the mean annual value of the formal standard deviation o. By comparison with the corresponding figures for the pole. one can estimate that a (2.5 days) of the measu-

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rement errors for UT1 is of the order of 1.3 x o. The improvement of UT1 observed in 1980 is mainly due to the impact of the chinese participation.

Relative Weight

cf(2,Sdays)

(a) OPT leAL ASTROMETRY

1967.0

1972.0

1977.0

1981.0

Fig.1. (a) Participation of the various techniques in the BIH evaluation of the coordinate x of the pole (5-day solution. table BC of Annual Report). (b) Square root of the pair variance for 5 days averaging time. The diagrams for y would be similar. ms

IJ

1.5

Fig.2. Formal standard deviation of the 5-day UT1 determination. The inclusion of new series is the result of numerous studies. After the adoption of the 1979 BIH System. it has been found that the results of the optical astrometry for the pole position agree fairly well with the data of the Doppler and SLR series. except for a constant or slowly varying bias. It was thus possible tc modify the weighting process concerning the annual terms. All series are used in the same way as optical measurements as explained by Feissel (1980). but the weight for the preservation of the BIH system of reference was splitted into two parts : a weight for the constant correction. and a weight for the annual correction. It was then possible. starting in January 1981. to determine the annual corrections to optical and CERI latitudes by reference to Doppler and SLR data (which receive no annual corrections). while all series contribute to the definition of the reference pole (Feissel, 1982). Concerning UT1. it was not yet possible to use the LLR and VLBI data. which are too sparse. The inclusion of the duration of day (LOD) measures from SLR. which would require an integration. raises some unsolved problems. but it is expected that these data should improve the evaluation of the short-term irregularities of UT1. The comparison of LLR and BIH series for UT1 reveals rather large differences

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(varying in a range of several ms) which are not explained. Among the numerous problems we have encountered we will mention a few ones on account to their general character. There is sometimes a bias of the order of 1 m between the pole coordinates derived by the DMA from different TRANSIT satellites. This might illustrate the danger of specialized models of the geopotential. Different constant corrections have been applied by the BIH for the different satellites. The tidal terms of UT1 with short periods (~ 1 month) raise difficulties on account of the lack of an agreed rule for dealing with them. We reiterate our wish that the IAU defines a form of UT1 corrected for these terms. We are faced to the problem of using different series derived from the same observations. To what extent are they independent?

Dissemination of the BIB results.

The BIH continues to evaluate the ERP weekly (under a JPL contract). monthly {Circular D). and yearly (Annual Report. which contains also experimental results from the new techniques). The results of Circular 0 (strong smoothing) are often used as standard reference. We suggest to continue to do so. since they are not modified by subsequent improvement. However we recall that better series appear in the Annual Reports. which should be used for geophysical research. The major changes are the increasing use of the GE Mark III. and the addition of new data in Circular 0 : a weak smoothing for UT1 and the corresponding LDD. the ERP from some networks. Numerous requests for special services have been answered. for instance.trans~ mission of data on tapes and cards. and by telex. particular smoothings ..• About 750 copies of the BIH Annual Report are sent yearly. B. GUINDT. Director. REPORT OF THE INTERNATIONAL POLAR MOTION SERVICE At the end of March 1980. Or. S. Yumi retired and Or. K. Yokoyama succeeded him as the Director of the IPMS. in accordance with the agreement at the General Assemblies of both the IAU at Montreal in August 1979 and the IUGG at Canberra in December 1979. The IPMS monthly raw and 1/20-year smoothed Earth rotation parameters (ERP) have been published regularly in Monthly Notes and Annual Reports. Basic data are astrometric observations. but the results of the connected element radio interferometry at Green Bank have been merged since the observation began. Inclusion of the results of other new techniques is also being considered. Three kinds of the ERP are given in the IPMS periodicals; 1) x. y and z from latitude data. 2) x. y. z and UT1 from time and latitude data. and 3) x. y. Z. T and UT1 from-time and latitude data. Periodic components in T. as well as those in z. are explained by the nutation errors. Drifts and jumps in station coordinates were adjusted when they became perceptably large. No correction for annual and semi-annual variations is· applied. Internal precision of the estimated monthly raw ERP are:

x 1979 1980

y

T

Time and Latitude

Latitude

Time UT1

~015 ~018 :016 ~0010

.012 .015 .014 .0008

x

y

z

':013 ':011 :019 .012 .010 .007

x

y

z

T

UT1

:010 :009 :008 :018 ~0011 .008 .008 .007 .015 .0009

Periodic and secular systematic differences of the IPMS ERP with reference to the ERP from new techniques have been monitored. In order to make more detailed comparison and to interpret the sources of the systematic differences. the IPMS is developing an algorithm to provide time-dense ERP in the system of new constants

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specified in the MERIT Standards. During the short campaign of the project MERIT from August to October 1980, the IPMS acted as an analysis center of classical techniques, namely, optical astrometry (Principal Coordinator - K. Yokoyama). Detailed report of the IPMS activities during the short campaign was presented at the MERIT Workshop held in May 1981 at Grasse, France. 85 optical instruments of 22 countries participated in the short campaign and contributed to the work of the analysis center. The IPMS ERP were estimated on monthly basis and transmitted to the coordinating center (BIH) of the Project MERIT through GE MARK-III system. The accuracy, as well as the precision, of the ERP derived from optical astrometry was remarkably improved due to the participation of 12 Chinese instruments of high quality. It is thus expected that the ERP derived from optical astrometry will have sufficient accuracy for comparing them with the results ofnewtechni~ues. In particular, for the comparison of the fine structure in UT1 variation, for example, the short periodic variation revealed in VLBI UT1 during the short campaign, optical astrometry will still play an important role in the coming main campaign. For the preparation of the main campaign, the IPMS has completed an algorithm to supply the ERP in the system of the MERIT Standards. This implies the adoption of the IAU 1976 System of Astronomical Constants, and the corrections for the variations of the vertical due to the Earth and oceanic tides, and for the deflection of light due to the relativistic effect. Unification of the global PZT star catalogs with a fundamental catalog is also under way. This will make it possible to exclude an uncertainty due to proper motion errors. Under the direction of the Working Group on Pole Coordinates originated at the General Assembly of the IAU at Brighton in 1970, the IPMS had been in charge of recalculating the past ILS observations. The final results were published as "Results of the International Latitude Service in a Homogeneous System, 1899.0 1979.0" by S. Yumi and K. Yokoyama (1980, Mizusawa, Japan). This volume gives ILS pole coordinates and the z-term on monthly basis with reference to the CID, based on the IAU 1964 System of Astronomical Constants. Magnetic tapes with individual latitudes of all northern ILS stations were distributed worldwidely to institutions and agencies related to investigations of the Earth rotation. General features of the newly derived pole coordinates are not very much different from those of the past reduction. However, it was confirmed that the annual z-term disappears when the nutation table of Wahr (1981) are adopted. Present situations of the ILS chain are as follows. The National Geodetic Survey which is in charge of observing the Earth rotation in the USA reported the closing of VZT stations of Ukiah and Gaithersburg on July 1, 1982. The NSG is concentrating its effort for monitoring the Earth rotation in the POLARIS Project. It was also reported that Carloforte in Italy and Kitab in the USSR will also suspend VZT observations in the near future due to the deterioration of the instruments. In order to interpret the past results of the ILS in terms of the new techniques, it is absolutely necessary to monitor displacements of the ILS stations with suitable new techniques. K. Yokoyama, Director. REPORT OF IAU/IUGG JOINT WORKING GROUP MERIT (SEPT. 1979, OCT. 1981) The proposal for Project MERIT, which had been endorsed at the IAU General Assembly in Montreal, was presented to the International Association of Geodesy and was endorsed by the Association and by the International Union of Geodesy and Geophysics at their meetings in Canberra in 1979 December. The IAU Working Group was reconstituted as a joint IAU/IUGG working group with added representation; Professor 1.1. Mueller became vice-chairman. The group developed the plans for the MERIT short campaign in more detail and appointed a steering committee to coordinate the activities during the Project. A review of the project and of the techniques to be used to monitor the rotation of the Earth was published (Wilkins,1980). The MERIT Short Campaign was held during the period 1980 August 1 to October

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31 to provide a realistic test of the operational arrangements that will be required during the MERIT Campaign in 1983/4. The campaign stimulated extra activity in all techniques, faster development of both laser ranging and VLBI, and a greatly increased level of interaction and cooperation between the scientists of the many disciplines and countries concerned in the project. In addition it provided a valuable set of observational data and results on both polar motion and the variations in the rate of rotation of the Earth. A Workshop to review the short campaign and to plan the main campaign was held at Grasse on 1981 May 18-21, and some of the results obtained during the campaign were presented on the following day at IAU Colloquium N°63. Brief reports were given in CSTG Bulletin N°3 and IAU Information Bulletin N°46. A ~ore extensive report on the short campaign is in preparation; it contains an account of the discussions at the Workshop, references to relevant papers, and a supplement giving details of the observations and results obtained during the campaign (\vilkins and Feissel, 1981). Information about the Project is published from time to time in the MERIT Newsletter which is distributed widely, on request. G.A. Wilkins, Chairman of the Working Group. REFERENCES BARLIK M., GALAS R., ROGOWSKI J., 1980: Proc. 4th Int. Symp. Geodesy and Physics of the Earth, in press. BENDER P.L., GOAD C.C., 1979: The Use of Artificial Sat. for Geodesy, Vol. II. BENDER P.L., 1981: Proc. IAU ColI. 56. BOUCHER C., PAQUET P., WILSON P., 1979: Proc. 2nd Int. Symp. Sat. Doppler Posi tionning. BRZEZINSKI A., KDLACZECK B., 1980: 4th Int. Symp. Geodesy and Physics of the Earth, in press. BRDSCHE P., SUNDERMANN J., 1979: Proc. IAU Symp. 82. BRDSCHE P., 1979: Astr. Nach. 300, 195. BRDSCHE P., KROHN J., SUNDERMANN J., 1980: Berliner Geowiss. Abh. Reihe A/Bd 19,5117 CALAME 0., GUINDT B., 1979: BIH Annual Rep. for 1978, 0-27. CALAME 0., 1979: BIH Annual Rep. for 1978, 0-49. CALAME 0., 1980: BIH Annual Rep. for 1979, 0-35 and 0-45. CALAME 0., 1981: BIH Annual Rep. for 1980, 0-13. CANNON W.H., PETRDCHENKD W.T., YEN J.L., GALT J.A., WALTMAN W.B., KNOWLES S.H., PDPELAER J.: 1979, Proc. Radio·Int. Techn. for Geodesy. CAPITAINE N., 1980a: Manuscripta geodetica, 5, 1. CAPITAINE N., 1980b: Proc. IAU Symp. 78, 87. CAPITAINE N., FEISSEL M., 1981: Proc. IAU ColI. 56, 135. CARTER W.E., 1981 : JGR 86, B3, pp 1653-1658. CHDLLET F., 1980: Proc. Int. Symp. Geodesy and Physics of the Earth. DAILLET S., 1981a: Geophys. J.R. Astr. Soc. 64, pp 373-380. DAILLET S., 1981: Geophys. J.R. Astr. Soc. 65, pp 407-421. DICKEY J.D., FLIEGEL H.F., WILLIAMS J.G., 1982: lAD Call. 63, p. 125. DITTRICH J., JDCHMANN H., 1980: Astron. i. Astrofiz., Kiev 42. DJURDVIC 0., 1979a: Publ. of Dept. Astr. Beograd, 9, pp 17-30. DJURDVIC D., 1979b: Publ. of Dept. Astr. Beograd, 9, pp 31-39. DJURDVIC 0., 1981: AA 100, pp 156-158. DZIEWDNSKI A. M., ANDERSON D. L., 1981: Phys. of the Earth and Planetary Interiors, 25. FANSELDW J.L., THOMAS J.B., COHEN E.J., PURCELL G.H., ROGSTAD D.H., 1979: Proc. IAU Symp. 82. FANSELDW J.L., 1980: BIH An. Report 1979, pp 075-76. FANSELDW J.L., 1981: BIH An. Report 1980. fEDDRDV E.P., 1980: Geodynamics and astrometry, Kiev pp 74-110. FEISSEL M., GUINDT B., 1980: Proc. IAU Symp. 78, 109. FEISSEL M., GAMBIS D., 1980: C.R. Acad. Sci. Paris, B 291, 271. FEISSEL M., 1980: Bull. geod., 54. 1. FEISSEL M., 1982: Proe. lAD Call. 63, p. 3.

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FLIEGEL H.F., DICKEY J.D., WILLIAMS J.G., 1982: Proe. IAU ColI. 63, p. 53. GAMBIS 0., NoUEL F., 1980: Bull. geod., 54, 108. GUINoT B., 1981: Proc. IAU ColI. 56, 125. HARA T., 1980: Publ. Int. Lat. obs. Mizusawa, 14, p.45. HoPFNER J., 1979: Gerlands Beitr. Geophys. 88, 3, pp 185-192. HoPFNER J., 1980a: Gerlands Beitr. Geophys. 89, 3/4, pp 182-186. HOPFNER J., 1980b: Astron. Nachr. 301, 1, pp 27-32. HoPFNER J., 1981 a: Trudy XXI As trometrices koj konferenzii SSSR, Tasch kent, pp 151-153. HoPFNER J., 1981b: Veroff. Zentr. Phys. der Erde, Potsdam, 63. HoPFNER J., SCHABACKER H.: Wiss. Z. Tech. Univ. Dresden 28, 3, pp 727-729. JAKS W., LEHMANN M., 1979: Wiss. Z. Techn. Univ. Dresden 28, H3, pp 750-759. JAKS W., LEHMANN M., 1980: Publ. Inst. Geophys. Polish Ac. of Sc., F6, 137. JAKS W., 1981: Acta Astronomica 31, 1 (Warsaw). JoCHMANN H., 1980: Gerlands Beitr. Geophys. 89, 3/4, pp 187-194. JoCHMANN H., 1981a: Astr. Nachr. 302, 4, pp 141-144. JoCHMANN H., 1981b: Veroff. Zentr. Phys. der Erde, Potsdam, 63. JoCHMANN H., 1981c: Veroff. Zentr. Phys. der Erde, Potsdam, 67. JOHNSTON K.J., SPENCER J.H., MAYER C.H., KLEPCZYNSKI W.J., KAPLAN G.H., McCARTHY 0.0., WESTERHoUT G., 1979: Proc. IAU Symp. 82, pp 211-215. KLEPCZYNSKI W.J., 1980: Project Merit, RGo, pp 17-20. KLEPCZYNSKI W.J., KAPLAN G.H., McCARTHY 0.0., JOSTlES F.J., BRANHAM R.L., JOHNSTON K.J., SPENCER J.H., 1980: Radio Interferometry Tech. for Geodesy, NASA Conf. Publ. 2115, pp 63-70. KoLACZEK B., 1979: Proc. IAU Symp. 82, pp 185-173. KoLACZEK B., 1980: Proc. 4th Symp. Geodesy and Physics of the Earth, in press. KoLACZEK B., GALAS R., BARLIK M., oUKWICZ M., 1980: Proc. IAUSymp. 78, pp 211-222. KoLACZEK B., TELEKI G., 1981: Proc. IAU ColI. 58. KOUBA J., 1981: An. de Geophys. , 1. LAMBECK K., 1980: The Earth's variable rotation, Geophysical causes and consequences , Univ. of Cambridge. LAMBECK K., HOPGOOD P., 1981: Geophys. J.R. Astr. Soc. 84, pp 87-89. MAJOR W., 1979: Wiss. Z. Tech. Univ. Dresden 28, 3, pp 736-737. MANABE 5., SAKAI 5., SASAo T., 1979: Publ. Int. Lat. obs. Mizusawa 18, 2. MANABE 5., 1981: Publ. Int. Lat. obs. Mizusawa, 15, p. 1. McCARTHY 0.0., 1979: Rev. Geophys. and Space Physics, 17, pp 1397-1403. McCARTHY 0.0., 1979: Proc. IAU Symp. 82, pp 85-68. McCARTHY 0.0., PERCIVAL 0., 1979: Proc. IAU Symp. 82, pp 53-54. McCARTHY 0.0., 1980: Publ. Int. Lat. obs. Mizusawa, 14, pp 1-34. McCARTHY 0.0., KLEPCZYNSKI W.J., KAPLAN G.H., JOSTlES F.J., BRANHAM R.L., WESTERHoUT G., JOHNSTON K. J ., SPENCER J .H., 1980: BIH An. Rep. 1979, pp 087-070. McCARTHY 0.0., 1981: Proc. IAU ColI. 56, pp 145-153. MEINIG M., JOCHMANN H., 1979: Wiss. Z. Techn. Univ. Dresden 28, 3, pp 739-742. MELCHIOR P., 1980: AA 875, pp 385, 368. MERRIAM J.B., LAMBECK K., 1979: Geophys. J.R. Astr. Soc. 59, pp 281-288. MERRIAM J.B., 1980: Geophys. J.R. Astr. Soc. 62, pp 551-561. MOCZKo J., 1980: Int. Koll. Geod. Astr. Mitteilung Techn. Univ. Dresden. MoLooENSKY S.M., 1981: Physics of the Earth, Moscow, n08. MONTAG H., GENoT G., WELMANN W., 1981: Proc. of the Merit Workshop (Grasse). NAKIBoGLU S., LAMBECK K., 1980: Geophys. J.R. Astr. Soc. 82,·pp 49-58. NGUYEN TRI LONG, 1979a: Vermessungstechnik 27, 2, pp 49-52. NGUYEN TRI LONG, 1979b: Wiss. Z. Techn. Univ. Dresden, 28, 3, pp 742-745. NGUYEN TRI LONG, 1979c: Veroff. Zentr. Phys. der Erde, Potsdam 58. OKAMOTO I., KIKUCHI N., 1981: Proc. IAU Colloq. n083.

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PAQUET P., Of VIS C., STANDAERT D., 1979: Proc. 2nd Int. Symp. Sat. Doppler Positioning. PAQUET P., 19BO: Phil. Tr. Roy. Soc. London, pp 237-244. SASAD T., WAHR J., 19B1a: Geophys. J. Astr. Soc. 64, pp 729-746. SASAD To, SATD To, 19B1b: Proc. of the 9th Int. Symp. on Earth Tides, NY, in press. SATD K., 1979: Publ. Int. Lat. Dbs. Mizusawa, 12, p. 55. SCHILLAK S., 19BO: Publ. Inst. Geophys. Pol. Acad. Sc. F-6/137. SUGAWA C., NAITO I., 19B1: Presented 6th European Reg. Meet., Dubrovnik. STDYKD A., 19BO: Published by Dbservatoire de Paris. VICENTE R.D., 1979: Proc. of the 9th GEDP Conference, Ohio State Univ. Report 2BC. VICENTE R.D., 19BO: Proc. IAU Symp. 7B, pp 139-151. VONDRAK J., 1979: Wiss. Z. Univ. Dresden 2B, 737. VONDRAK J., 19BOa: Bull. Astr. Inst. Czekosl. 31, B9. VONDRAK J., 19BOb: Proc. of the 4th Symp. Geodesy and Physics of the Earth. VONDRAK J., 19B2: Bull. Astr. Inst. Czechosl. 33 (in press). WAHR J.M., 19B1: Geophys. Astr. Soc. 64, p 705 WAHR J., SASAD T., SMITH M., 19B1a: Geophys. J. Astr. Soc. 64, pp 635-650. WAHR J., SASAD T., 19B1b: Geophys. J. Astr. Soc. 64, pp 747-765. WILLIAMS J.G., MELBOURNE W.G., 19B1: Proc. IAU Call. 63. WILSON C.R., VICENTE R.J., 19BO: Geophys. J.R. Astr. Soc. 62. WU SHOUXIAN, HUA YINGMIN, WANG SHUBE, 19B1: Scientia Sinica 7, pp B47-B54. WU SHDUXIAN, WANG SHUBE, HUA YINGMIN, 1979: Acta Astronomica Sinica, 20, n012. WILKINS G. A., 19 B0: Review of the techniques to be used during Proj ect Merit. RGD Pub 1. WILKINS G.A., FEISSEL M., eds. 19B1: Project Merit, Report on the short campaign. RGD Publ. YATSKIV Ye S., GUBANOV V.S .• 19BO: GeOdynamics and astrometry. Kiev,pp 110-120. YATSKIV Y.S., 19BO: Proc. IAU Call. 56, pp 155-165. YODER C.F., WILLIAMS J.G., SINCLAIR W.S., PARKE M.E., 19B1a: JGR B6, pp BB1-B91. YODER C.F., WILLIAMS J.G., PARKE M.E., DICKEY J.D., 19B1b: An.de Geophys. 37. The following references are those of Astronomy and Astrophysics Abstracts: 25.032.05B, 044.001, 044.009, 044.013, 044.0BB, 045.003, 045.004. OB1.007 26.043.001, 044.001, 044.007 27.031.530,031.531,032.004,032.023,032.024, 041.01B, 041.021, 041.046, - 041.050, 043.00B, 043.011, 043.012, 043.014, 044.004, 044.010, 044.014, 044.015, 044.034, 045.001. 045.011, 045.011, 045.012. 045.033, OB1.063, OB1.073. 2B.044.035. P. PAQUET

President of the Commission.

20. POSITIONS AND MOTIONS OF MINOR PLANETS, COMETS AND SATELLITES (POSITIONS ET MOUVEMENTS DES PETITES PLANETES, DES COMETES ET DES SATELLITES) PRESIDENT: G Sitarski VICE-PRESIDENT: E Roemer ORGANIZING COMMITTEE: Yu V Batrakov, M P Candy, F K Edmondson, Y Kozai, t Kresak, B G Marsden, J Schubart, G E Taylor, P Wild, Y-Z Zhang I.

INTRODUCTION

An avalanche of discoveries pertaining to the satellite and ring systems of Jupiter and Saturn followed from the encounters of Pioneer 11 with Saturn, of Voyagers 1 and 2 with both Jupiter and Saturn, and from the passage of the Earth through the Saturn ring plane, all of which occurred during the triennium. The first comet discovery from a spacecraft also occurred during the same interval, a coronagraph experiment on the satellite P78-1 apparently catching a Kreutz sungrazer in the last hours before it impacted the Sun on 1979 August 30. Several successfully observed occultations of stars by the Uranian ring system, by minor planets, and possibly by satellites of Neptune and Pluto testify to efforts inspired by the Commission's Working Group on Prediction of Occultations.

Although there seems to be a general increase in interest in comets, particularly in their physical characteristics, arising from planning for the impending return of P/Halley, as well as from studies relating to experiments for future spacecraft missions, the burgeoning activity does not seem to extend to astrometric observations, even of rather bright comets. Part of the reason for this may be that such observations are no longer given the prominence they once enjoyed on the !AU Circulars. Initial observations of new and recovered comets still appear there, of course, but the bulk of the observations are now published in the Minor Planet Circulars/Minor Planets and Comets. The form of the MPCs has been modified recently in an attempt to give greater prominence to the observations of comets. But part of the problem is merely a relative one, in that the number of astrometric observations of minor planets has exhibited such a tremendous surge in recent years. International meetings of interest to the Commission were the colloquium 'Asteroids', held in Tucson, Arizona, in 1979 March; and IAU Colloquium No. 61, 'Comets', held also in Tucson, in 1981 March. Publications derived from two international meetings held earlier also appeared during the triennium: !AU Symposium No. 81, 'Dynamics of the Solar System', held in Tokyo in 1978 May; and 'Natural and Artificial Satellite Motion', held in Austin, Texas, in 1977 December. Commission 20 notes with regret the passing of the following members: P Herget (1908-1981), H Hirose (1909-1981), M Itzigsohn (18 -1978), J G Porter (1900-1981) and K Reinmuth (1892-1979). As founder-director of the Minor Planet Center and a former president of the Con~ission, Herget dominated the study of minor planets for several decades, applying his unique experience with automatic computing methods to rescue the subject following the disruption caused by World War II. As director of the Tokyo Observatory Hirose was for many years the leading figure in research on minor planets and comets in Japan; his first work on orbits and identifications was done more than half-a-century ago, and he was also actively involved in the Tokyo observational program. As leader of the La Plata program, Itzigsohn was responsible for the surge in observational and computational activity on minor planets in Argentina following World War II. As president of the subcommission on comets (later as chairman of the Working Group on comets) and as director of the Computing Section of the British Astronomical Association, Porter was responsible for the 195

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increase in the number and reliability of predictions for the returns of periodic comets during and after World War II; the first of the recent editions of the Catalogue of Cometary Orbits (1960) was produced under his guidance. As an early participant and for a quarter of a century the leader of the observing program at Heidelberg, Reinmuth holds the record for the number, almost 300, of discoveries of numbered minor planets. Information for the sections of this report on Minor Planets, Comets, Satellites and Prediction of Occultations has been compiled by B G Marsden, L Kresak, Y Kozai and G E Taylor, respectively. Due to unusual circumstances, the president of the Commission was unable to undertake the preparation of the Commission Report in final form. That responsibility has therefore fallen to the undersigned, who owes deep appreciation not only to the Working Group chairmen named above but to all individuals who provided information for the report. As in the past, Astronomy and Astrophysics Abstracts numbers are generally used for the references. II.

MINOR PLANETS

GENERAL The Minor Planet Center has completed its first full triennium of operation at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, under the direction of B G Marsden. C M Bardwell was promoted to Associate Director in April 1981, and valuable assistance has also been variously provided by D W E Green and E Fogelin. As previously, the Minor Planet Circulars have been published in monthly batches. The steady increase from some 500 issues during 1979 to more than 800 during 1981 is a dramatic indication of the general surge of activity in the Commission in the area of minor planets. This surge involves astrometric observations and orbit computations in appropriate proportions: the machine-readable file of observations, which contained almost 230 000 entries when the first distribution of copies to interested users was made early in 1981, is now growing by some 10% per year, while the corresponding increase in orbital studies means that minor planets are now receiving permanent numbers at the unprecedented annual rate of more than 170. a)

The increasing rate of new numberings has also had a noticeable effect on the size of the annual volumes of Efemeridy Malykh Planet, which continue to be prepared at the Institute for Theoretical Astronomy in Leningrad by N V Ashkova, V A Isvekov, F B Khanina and V A Shor, under the direction of Yu V Batrakov. The 1982 volume contains 252 pages. Transfer to the BESM-6 computer enabled the production of the Efemeridy to be greatly automated. An important change, which greatly augments the scope of this publication, has been the presentation of high-precision orbital elements for all the minor planets for a new standard OSCUlation epoch each year; although the opposition ephemerides are still given as before, many users are finding it convenient to calculate ephemerides more suited to their individual needs directly from the current osculating elements. 'Asteroids', the proceedings volume of the international colloquium organized by T Gehrels in Tucson in March 1979, is an excellent up-to-date general reference on the subject. Although there is an emphasis on physical studies, many of the contributions are relevant to the work of Commission 20, particularly the definitive compilation, by J G Williams, of proper elements and family memberships for minor planets 1-1796. b)

OBSERVATIONS AND ORBITS The most consistently complete observational program continues to be that conducted by N S Chernykh and his four collaborators at the Crimean Astrophysical Observatory. The number of observations made is now in excess of 3000 per year, about 20% of them referring to numbered planets. As many as 1300 unnumbered objects have been recorded in one year, and about one-third of the minor planets receiving

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new permanent numbers result from this program. The observing programs led by E Bowell at the Lowell Observatory and by A Mrkos at the K1e~ Observatory are also especially worthy of note. Although the number of observations is rather less than in the Crimean program, the numbered planets are well covered, and more than 100 unnumbered objects are recorded in each program ea.ch year. A significant feature of these programs has been the immediacy with which the plates are measured; the resulting positions are generally published in the MPCs within a month or two of their being obtained. The Lowell program makes use of a microdensitometer, rather than a conventional measuring engine. Although the reduction process is more complex, a plate containing many objects can be measured more quickly, and tests show that the results are quite as accurate as those obtained by the conventional procedure. Other wide-field programs currently yielding a SUbstantial number of observations of faint or unnumbered minor planets are conducted by C Torres and his colleagues at Cerro El Roble, by H Kosai and K Hurukawa at the Tokyo Observatory's Kiso station, by F BOrngen at Tautenburg, by C U Cesco and his associates at the Felix Aguilar Observatory's El Leoncito station, and under the general direction of Y-Z Zhang at the Purple Mountain Observatory. A large number of observations have also come from extensive international collaborations, notably by S J Bus, E Helin, J Gibson and C Kowal at Palomar and Siding Spring; and by H Debehogne, R R de Freitas Mourao, G De Sanctis, C-I Lagerkvist, L D Schmadel, J Schubart, H-E Schuster, R M West and V Zappala at the European Southern Observatory, the Uppsala Southern Station, Kvistaberg and Marseilles. Conventional reflectors, such as those used in the programs under the direction of R E McCrosky at the Oak Ridge Observatory (formerly Harvard Observatory's Agassiz station) and by A C Gilmore and P M Kilmartin at the Mt John Observatory, frequently provide the important last-of-the-season observations of new discoveries. The brighter minor planets have been well observed at Nice (by B Milet), Bucharest (C Cristescu), Sydney (w H Robertson) and at several observatories in the USSR, as well as by amateur astronomers in Japan (T Seki, T Furuta, M Takeishi), England (B Manning and others), Australia (D Herald), West Germany (R Hempel and others) and East Germany (M Gressmann). A promising new source of observations is a real-time television survey being made at the Lincoln Laboratory's New Mexico installation (L G Taff) . C J van Houten and I van Houten-Groeneveld have now essentially completed the measurement of the additional plates from the Palomar-Leiden survey. The observations, which number more than 16 000, are to be included in the Minor Planet Center's machine-readable file. Several hundred new and improved orbits, mainly calculated by P Herget, will be published shortly. Accurate positions have continued to be measured on request from older plates at the Goethe Link Observatory (under the general direction of F K Edmondson), the Turku Observatory (under the direction of L Oterma) and the Lowell Observatory (H L Giclas, Bowell). It has also been possible to get occasional accurate positions from the important collections at Johannesburg (via J Churms), and Budapest (West, L Kresak). In connection with the publication of the annual Efemeridy volume, Khanina and her associates at the Institute for Theoretical Astronomy have improved the orbits of the numbered minor planets at a rate of about 100 per year. Preliminary orbits and search ephemerides are computed by G R Kastel' for many of the objects observed in the program at the Crimean Astrophysical Observatory. A number of orbit improvements and integrations for numbered minor planets have been made by M A Dirikis at the Latvian state University, Riga.

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Interest in finding identifications among unnumbered objects at different oppositions has remained at a high level. Such work is still carried out with significant success by hand, as it has been for many years, by 0 Kippes (Wurzburg). Others, notably Herget (Cincinnati) and the Japanese amateurs T Urata and H Oishi, as well as Bowell, Marsden and Bardwell have generally used computer searches to find identifications. Williams (Jet Propulsion Laboratory) has led the effort to make searches for past images of specific objects on Palomar Schmidt plates. The resulting improved orbits have been determined generally by Herget, Urata, Nakano, Marsden and Bardwell. Schmade1 (Astronomisches Rechen-Institut) has recently conducted a thorough search of the observations of unnumbered minor planets for previously unsuspected identifications with numbered objects. In the report for the 1976-78 triennium it was noted that the number of lost numbered minor planets had been reduced to 23. Even more concerted searches for identifications have reduced this number further, so that now only eight objects are lost out of the total of 2495. The principal authors of the 15 recent successes are: L K Kristensen, Aarhus (452, 682, 730, 1537, 1538); Schmade1 (843, 1370); Kippes (1037, 1198); Chernykh (1020); Marsden (612, 1229, 1316, 1465); and Bardwel1 (603). c)

THEORETICAL INVESTIGATIONS C Froeschle and H Scholl (25.098.004) have continued their work on the depletion of minor planets in the outer part of the belt. F A Franklin, M Lecar and D N C Lin (26.098.071; 27.098.135) have concluded that the depletion cannot have an entirely graVitational cause and have examined conditions for the production of the Kirkwood gaps. On the other hand, S F Dermott and C D Murray (29.098.010) have concluded that the gaps are formed by gravitational processes acting on individual objects. T A Heppenheimer (26.098.027; 28.042.042) also investigated the origin of the gaps, and he has extended the Brouwer-van Woerkom solution for determining proper elements. L Zaleski (26.098.115) made a statistical investigation of the formation of the belt, while V F Zheverzheev (25.098.056; 27.098.006) discussed the probability distribution of several parameters of the belt. Z Knezevic (27.098.115) examined the statistical stability of the sample of numbered minor planets. B Garfinkel (28.042.040) published the third paper in his series on the theory of motion of Trojans, and B Erdi (26.098.004) showed that the longitudes of perihelion of Trojans are twice as likely to circulate as to librate. R Bien (27.042. 004; 27.098.074), continuing his earlier work on the Trojans, addressed the question of possible differences between objects of high and low inclination. C F Yoder (26.098.073) considered the general problem of the origin of Trojans, and M De1va and R Dvorak (26.042.012; 29.042.059) studied TrOjans in terms of the elliptic threebody problem. S G Zhuravlev (25.098.050; 28.098.022) examined the feasibility of using quasiperiodic solutions of the three-dimensional restricted problem as intermediaries in orbital theories for resonant planets and investigated the asymmetry of the Kirkwood gaps. G T Arazov and S A Gabibov (26.098.005) utilized the two-fixed-center problem to obtain an intermediary in the 2:1 case. Using Schubart's averaging model Bien (27.042.034) found statiQnary solutions at various resonances, and S I Ipatov (27. 042.100) examined the evolution of resonant orbits in the planar restricted problem. A N Simonenko, L M Sherbaum and V G Kruchinenko (26.042.046; 26.098.072; 26.098.106; 28.042.029) investigated the evolution of orbits near the 3:1 resonance, and F A Karminskij (26.098.050) studied this resonance as it applies to objects observed in the P-L survey. T Kiang (27.098.134) continued his earlier work on the difference between the 2:1 and 3:2 resonances. Y Kozai (27.098.109) introduced a new criterion for defining families of minor planets, namely, the semimajor axis, the projection of the angular momentum on Jupiter's orbit plane, and the minimum inclination as a function of the argument of perihelion. In an examination of the dispersion of members of Hirayama families, W-H Ip

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(26.098.083) shed light on the general fragmentation processes in the minor planet belt. Williams and J Faulkner (Icarus 46, 390, 1981) made a detailed study of the positions of the secular resonances. Z Vrcelj (26.042.010) derived a new invariant relation in the elliptic restricted problem, with particular reference to the SunJupiter-minor planet case; and D Olevie and D Burovic (27.098.143) made a statistical study of Jacobi constants. S Oikawa and E Everhart (25.098.006) investigated the long-term motion of (2060) Chiron, concluding that this object is more likely to be evolving toward, ra.ther than away from, the inner part of the solar system; a similar investigation also was made by Scholl (26.098.074). On the other hand, R C Smith (27.098.082) considered the possibility that Chiron was ejected from the main belt of minor planets. Scholl (26.098.023) also summarized the dynamics of Apollo objects, and G W Wetherill (25. 098.020; 25.098.039) continued his study of the likely processes involved in the formation of Apollo and Amor objects. M A Vashkov'yak (29.098.009) worked on the evolution of the orbits of more than 20 atypical minor planets, and KresAk (27.098. 072) reviewed the general problem of dynamics of interplanetary bodies, with particular reference to the interrelation of comets and minor planets. A P Mayo (25.098.069) derived analytical expressions for the perturbations of planetary orbits by the minor planet belt. J L Simovljevitch (26.042.034; 27.098.142; 29.098.062; 29.098.063) developed a procedure for estimating the effects of the mutual perturbations of two minor planets, while J Lazovic and M Kuzmanoski (29.098. 059; 29.098.060; 29.098.061) discussed the problems of close approaches of minor planets to each other. A W Harris and J A Burns (26.098.013; 26.098.014) pointed out that if there is a real trend toward more rapid rotation among very small minor planets, many such objects must possess significant internal strength. L B Ronca and R B Furlong (26. 098.114) also found that small objects are quite capable of maintaining irregular shape. S J Weidenschilling (29.098.038; 29.098.085) considered the general problem of rotation of minor planets, citing a case for the contact-binary nature of (624) Hektor (29.098.082). The likelihood that many minor planets possess satellites has continued to be promoted at length, notably by R P Binzel and T C Van Flandern (25. 098.014; 27.098.139). While the claim might be somewhat acceptable theoretically (Harris, 26.098.032; J R Donnison, 25.098.025) the observational support remains far from convincing (H J Reitsema, 26.098.002; E K Hege, W J Cocke, E N Hubbard, J Christou and R Radick, 28.098.037; P D Maley, 28.098.088). G Sitarski (26.098.065) demonstrated a method for including second-order terms in orbit-corrections problems, with special application to the case of (2101) Adonis, for which a similar solution was derived by G Schrutka and Dvorak (Sitzungsber Osterreich Akad Wiss, in press). Dvorak and C Edelman. (26.031.519) described a new filtering technique for orbit determination, while J Chapront and P Rocher (27.042. 092; 27.098.014) considered the use of Chebyshev series in computing the motions of minor planets. T V Bordovitsyna, V A She fer and B T Kharin (Astr Geodez 8, 54 and 81, 1980) demonstrated the use of Kustaanheimo-Stieffel transformations for the computation of special perturbations. R L Branham (26.098.039; 27.043.003; 28.041.028) used observations of the minor planets (6), (7), (8), (9) and (15) to determine corrections to the FK4 equator and equinox, showing how an ideal program of observations might be conducted in order to obtain an optimal result; he also examined the general problem of the least-squares solution of ill-conditioned systems. V I Orel'skaya (27.041.026) continued her extensive work on a similar program, and Kristensen (28.041.014) has determined corresponding corrections from observations of (51) Nemausa. In connection with this work, P Hemenway (27.041.035) discussed the use of 'crossing-point' observations of minor planets.

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III.

COMETS

a)

DISCOVERIES, RECOVERIES AND ASTROMETRIC OBSERVATIONS During the interval 1979 January 1 - 1981 November 1, 14 long-period comets and 7 new short-period comets were discovered, and 21 previously known short-period comets were recovered. Half of the discoveries of long-period comets were made visually, confirming that the contribution of amateur comet searchers, as WA Bradfield, with three comet discoveries in the triennium, is still very important. Most of the discoveries of new short-period comets were made with large Schmidt telescopes (Siding Spring, Palomar) and most of the recoveries either with large Schmidts (La Silla) or large reflectors (Oak Ridge). It is noteworthy that for the first time in history a slight majority of the discoveries and recoveries came from the Southern Hemisphere: 11 to 10 in both cases. The annual number of comets which received provisional designations exceeded 20 for the first time in 1980. These statistics refer only to well observed objects with determinate orbits, meeting the criteria for definitive designation. In addition, there were several unconfirmed discoveries or insufficiently observed objects. From among these, only 1979h Kowal was recorded on three nights; an approximate orbit by Marsden (26.103. 521) indicated that it was very probably a short-period comet. Only two observations and, hence, no orbital elements are available for 1980p Helin-Dunbar (later identified as a ghost of ~ Leo), two comets found by C T Kowal (26.103.007), one by N S Chernykh (25.103.002), and one by P Stattmayer (IAU Circ 3638). While the IAU Telegram Bureau reacted immediately to each announcement, and follow-up observations were attempted at several observatories, no further observations were obtained of any of these objects. The need for early examination of each suitable wide-field plate must be emphasized, since in most of the cases cited a delay of several weeks was the main reason for loss of the comet. The first comet discovered from a spacecraft, designated 1979 XI Howard-KoomenMichels, was found by R Howard (IAU Circ 3640) in data belatedly available from the orbiting SOLWIND coronagraph developed and operated by N Koomen and D J Michels, Naval Research Laboratory, Washington. Although a range of solutions was consistent with the limited data on position and brightness of the head and tail, calculations by Z Sekanina (IAU Circ 3647) leave little doubt that the comet was a Kreutz sungrazer that actually impacted the Sun on 1979 August 30. Detailed inspection of the Palomar Sky Survey plates by G Auner, J Dengel, H Hartl and R Weinberger (26.103.006; 27.103.012; 28.103.006) revealed three comet trails unnoticed earlier. One of these was identified by T Nomura (IAU Circ 3588) with p/Gunn, thus extending the observational history of this annual short-period comet by more than two revolutions. One rediscovery, that of P/Schwassmann-Wachmann 3, 1930 VI = 1979g, missed for 8 returns, deserves special mention. Being situated 24 0 from the predicted poSition, it was reported as a new comet by J Johnston and M Buhagiar (26.103.261). The corresponding error of 34 days in the time of perihelion passage was surprisingly large for a comet observed for nearly four months in 1930, during the second closest approach of a comet to the Earth in this century. In 1979-81 two long-period comets became easy naked-eye objects (19791 Bradfield: 4~5 and 1980t Bradfield: 3~5), and two short-period comets approached the naked-eye limit (P/Encke and P/Tuttle); yet there was no really spectacular object like 1976 VI West or 1973 XII Kohoutek. There was also no continuation to the series in 1974-77 of five discoveries of comets with perihelia outside the orbit of Jupiter. Undoubtedly the most interesting discovery was that of 1980b Bowell. This comet was located a mere 2 0 from Jupiter, and only the orbit determination by Marsden (27.103. 661) showed that it was in fact 1.7 AU beyond that planet. It passed Jupiter at a distance of 0.23 AU in 1980 December, this being the closest approach of a comet to Jupiter included within an observed orbital arc. Inasmuch as the orbital inclination was the lowest of all known long-period comets, the perturbations were unusually

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strong, leading to the highest hyperbolic excess on record. This will result in an ejection from the solar system with a residual velocity of nearly 4 km/s. The discovery circumstances raised the problem, discussed by Marsden (28.103.221), of how to compute the preliminary orbit if a comet is discovered during an encounter with Jupiter. The problems of rediscoveries of long lost comets were treated by N A Belyaev (25.102.003) and KresaK (Bull Astr Inst Czech 32, 321, 1981). According to the latter, ephemeris-aided searches appear feasible for only three lost one-apparition comets: P/Barnard 1, P/Swift and P/Giacobini. The awaited parent comet of the Perseid meteor stream, P/Swift-Tuttle, has not yet been recovered in spite of continuing searches, but the uncertainty in its revolution period leaves open the possibility of a recovery later in the decade. Extensive searches for P/Halley remained without success. Since the ephemeris should be reliable, the negative result imposes limits on the size and albedo of the nucleus. Nearly 3000 astrometric observations of 54 different comets were published between 1979 January 1 and 1981 November 1 in the MPCs. About 55% of them were from earlier exposures, with nearly 600 positions measured by E Roemer on her 1967-76 Kitt Peak and Catalina plates representing a major contribution. Together with the results of six other observatories at Oak Ridge, Perth, Klet, Geisei, Nice, and Cerro el Roble, with 100 to 200 positions each, it constitutes half of the data collected. The other half of the measurements was obtained at 80 different observatories distributed over the world. It is noteworthy that more than 20% of the observations were from the Southern Hemisphere and that this share was increasing, thus providing a stronger observational base for orbit determinations. Thanks to the indefatigable efforts of Marsden and his associates at the IAU Minor Planet center, remarkable progress has been made in data acquisition and handling, leading to assembly of a rapidly expanding file of astrometric observations of comets as well as of minor planets. The data on recent comets will soon be available in machine-readable form. Unfortunately, a simultaneous restriction of publication in the IAU Circulars to the discovery, recovery, and immediate-post-discovery observations, in force since 1978, seems to have had some negative impact (Marsden, IAU Circ 3531). The situation has improved recently, but is still unsatisfactory as regards short-period comets, for most of which less than 10 astrometric observations per apparition become available. To quote just the most striking examples, there seem to exist only two observations of P/Reinmuth 2 and P/Finlay, and three of P/Daniel and P/Harrington - in each case from a single observatory, often Perth. The situation is better with confirmatory post-discovery observations of new Northern comets, where the Oak Ridge observers, with guidance from R E McCrosky and Marsden, cooperate most effectively with the IAU Telegram Bureau. It must be emphasized that followup observations of all periodic comets are essential both for investigation of nongravitational effects in their motion and for satisfaction of the increasing demands on the accuracy of ephemerides by astronomers contemplating radio, radar, infrared or ultraviolet observations. b)

ORBITS AND EPHEMERIDES Preliminary orbits and ephemerides for newly discovered comets were mainly computed by Marsden and appeared regularly in the IAU Circulars and in the MPCs. A parallel service, mostly using the same computations, was provided by the Kometnyj Tsirkulyar, edited by S K Vsekhsvyatskij in collaboration with D A Andrienko and K I Churyumov, and by the Japan Astronomical Circular, edited by M Takeishi. Dozens of orbit improvements were performed, in particular by Marsden and by S Nakano (Nakano wa Kangaeru noda, Nos. 344-407, 1979-81). Redeterminations of the orbits of 38 ancient and mediaeval comets{with several tentative identifications with periodic comets of Halley type, were published by I Hasegawa (26.103.001). R J Buckley (25.103.001; 26.103.005) improved the orbits of 23 nineteenth-century comets and other authors did the same for smaller numbers of objects. According to an

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orbit redetermination by W Landgraf (28.103.005) 1937 II Wilk, with P = 195 yr, falls into the middle of the gap between long- and short-period comets. As noted by Kresak (29.102.023), the long-period comets occupying the upper boundary of this gap exhibit a definite clustering of perihelion passages which is difficult to explain. Our knowledge of the motions of short-period comets, and of the nongravitational forces acting on them, has been extended by a number of new solutions linking individual comet apparitions or integrating the motion of selected comets over centuries. The most comprehensive results include those on PjPons-Winnecke by E A Reznikov (25.103.401), PjDaniel by L M Belous (26.103.441), PjWolf and PjAshbrook-Jackson by E I Kazimirchak-Polonskaya (27.103.151; Trudy Inst Teor Astr 18, 1981), PjChernykh by Kazimirchak-Polonskaya and Chernykh (27.103.221), PjHalley and PjOlbers by H Q Rasmusen (27.103.705), PjCrommel1n by E D Kondrat'eva (27.103.731), P/SchwassmannWachmann 3 by Belyaev and S D Shaporev (Byull Inst Teor Astr 15:4, 1981), PjBrooks 2 by I Yu Evdokimov and Yu V Evdokimov (Komety i Meteory 29, 73, 1981), PjDenningFujikawa and P/Schwassmann-Wachmann 2 by Nakano (Nakano wa Kangaeru noda 344, 1979 and 405, 1981), and PjShajn-Schaldach and PjWhipple by EM Pittich (Bull Astr Inst Czech 32, 340, 1981). Especially interesting is the case of P/Boethin. D Benest, R Bien and H Rickman (27.103.121) have found this comet to librate around the 1:1 resonance with Jupiter in a motion resembling an extremely distant satellite. It appears that satellite captures of short-period comets by Jupiter, in the sense of a temporary reduction of their jovicentric velocity below the parabolic limit, are relatively frequent events; A Carusi and G B Valsecchi (29.099.028) have identified 11 such cases in the recent history of 7 comets subject to low-velocity encounters with Jupiter. D K Yeomans and T Kiang (27.103.701; MNRAS 197, 633, 1981) integrated the motion of P/Halley back to -1404, using some unusually accurate old Chinese observations to constrain the comet's orbit. A good representation of all observations was obtained under the assumption of constant nongravitational forces, which would indicate slow aging and a relative stability of the spin axis. Extended ephemerides and other data relevant to the next return were published by Yeomans in his Comet Halley Handbook. The third edition of Marsden's Catalogue of Cometary Orbits (25.002.022) lists 1027 apparitions of 658 different comets up to the end of 1978. A fourth edition is planned for early 1982. Of the special catalogs, that by Hasegawa (27.002.052) lists ancient, mediaeval and naked-eye comets and that by V P Tomanov (26.103.010) gives various orbital and physical characteristics of 118 short-period comets. As regards computing techniques, G Sitarski (26.042.033) developed an efficient method for the integration of motion using recurrent power series, with automatic adjustment of the optimum step length at each step. Yu V Batrakov and E N Makarova (27.042.010) adapted the Encke method to a coincidence of initial perturbed and unperturbed velocities and accelerations, thus increasing its efficiency for handling large perturbations. P E Zadunaisky (26.042.019) developed a method for estimation of global errors propagated in the numerical solution of the N-body problem. The problem of the accuracy of the determination of short-period cometary orbits was treated by V V Emel'yanenko and N Yu Emel'yanenko (Opredelenie koordinat nebesnykh tel 19, Riga 1981). On the motion of P/Taylor, V V Emel'yanenko (Kometn Tsirk 273, 1981) showed how Jupiter's perturbations can improve the determinacy of the orbit a case similar to that of P/du Toit-Neujmin-Delporte noted earlier by Marsden. This effect may become important in the searches for long-lost comets; Emel'yanenko suggests supplementing ephemerides of such comets with the evaluation of differential perturbations as a function of 6T. Empirical formulae for estimating the accuracy of l/a were derived by Kresak (26.102.006); they permit identification of those long-period comets for which improvements of the available orbital data appear feasible, and the prediction of the determinacy of l/a in different stages of observation.

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Belyaev and Yu V Chernetenko (27.102.005) have compared Dubyago's and Marsden's methods for determining nongravitational effects in the motion of short-period comets, and found a good quantitative agreement. Statistical features of the nongravitational effects on long-period comets were investigated by P R Weissman (25.102.013), who showed that for q 100 km. Webb (1981) emphasized that while below 95 km diffusion is determined by 2D+, above this height the diffusion coefficient depends on train orientation to the magnetic field, electron line density and the background ionization density. The findings are in accord with theoretical work. Diffusion of a meteoric plasma containing two species of positive ion was considered by Novikov et aZ (1981) while the details of coulomb collisions in a train are given by Levitsky (1978). Ionization loss in meteor ,trains was described by Bibarsov et aZ (28.104.059) and Baggaley (22.104.013) related train metal ion chemistry to the limitation in duration of very long meteor radar echoes and also considered (Baggaley 1979a) the effect of very intense meteoric ionization on LF propagation. Sporadic meteor

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echo durations observed by McIntosh and Hajduka (1977) were in accord with simple metal reactions governed by 03 and 0, and the diurnal variations are explained well by the model given by Baggaley (25.104.034) for the dependence of observed overdense meteor echo duration distributions on mean meteor velocity. The recombination of ionization in underdense plasma was shown to be negligible (Baggaley 25.104.039). Concern for the validity of estimates of scale height and D from echo studies (Forti, 21.082.027) was shown to be unfounded by Baggaleya(1979b). Multifrequency observations of echo decay rates and a bistatic experiment were undertaken to delineate train irregularity scales and wind shear (Baggaley 28.104.015). The influence of non-uniform winds on measurements of D was discussed by Novotny (21.104.020) and the statistical analysis of scatter dia~rams of Da versus height was discussed by Baggaley (28.104.023). Hawkes and Jones (22.104.025) modelled initial radii (r i ) from a consideration of meteoroid rotation. Two wavelength studies of Baggaley (28.104.016) found a linear relationship between r. and meteor velocity, with r. ~ p-a where p is the atmospheric density, and 1 r (100 km) = 1.5m, a = 0.42~ In a triple wavelength study of meteors with density ~ 101Sm- 1 Baggaley and Fisher (28.104.002) found r(lOO km) 5.Om, a = 0.63. Using underdense echoes Baggaley (198la) determined r(l15 km) = 1.8m, suggesting that a = 0.26. From comparisons between sodium nightglow, lidar data and the magnitude of enduring visual meteor trains, Baggaley (21.104.001) suggested that the sodium catalytic mechanism is responsible for persistent train luminosity. Baggaley and Cummack (25.104.033) considered the mechanisms limiting the life of emitting species in a train and showed that' 03 depletion, molecular and turbulent diffusion and surface brightness reduction would limit the. duration of visual trains to less than one hour for a large fireball meteor; the figures accord well with the known statistics of the occurrence of trains. For trains enduring for some minutes the formation of metal oxide ions and subsequent dissociative recombination to produce excited metal atoms was proposed by Poole (1978) though Baggaley (1978) pointed out that the crude available data on spectral distribution of train light argues against such a mechanism. Hapgood (28.104.007) obtained an estimate of the photon emission in the near infra-red of a long enduring meteor train. He and Baggaley (198lb) put forward alternative mechanisms for the emission. There is strong evidence that the 5577A emission from atomic oxygen recorded in meteor wake spectra is a result of charge transfer followed by dissociative recombination (Baggaley 21.104.003, 28.104.023). The cause of the inverse correlation between meteor rates (visual and radar) and sunspot numbers variations continues to be sought. Lindblad (21.104.027) found that a 20% decrease in meteor rates occurred about 3 days after the passage of a solar wind sector boundary. Ellyett and Kennewell (28.104.012) have shown that for mass distribution indices s > 2.0 a decrease in scale height H would yield an increase in observed rate; for s = 2.5 a 30% decrease in H would be expected to produce an increase of 24% in radar rate. Elford (28.104.024) showed that differences between summer and winter standard atmospheres can produce the observed changes in rates.

IX

TEKTITES

B.P. Glass.

The last few years have witnessed a renewed interest in tektite research. There appears to be at least three reasons for this: (1) application of techniques developed in the study of lunar samples to terrestrial problems; (2) the discovery of tektite-like glasses associated with an impact crater (Zhamanshin) in the USSR; and (3) the possibility that large impacts (including tektite events) may have triggered climatic changes and extinctions.

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Some authors maintain that Libyan Desert glass is a kind of tektite; however, e.m.r. spectroscopy indicates that, unlike tektites, Libyan Desert glass was fused under oxidizing conditions (Weeks et aZ 1980). Tektites (probably Australasian) were reported from Northern Thailand (Yabuki et aZ 1981), but papuanites (translucent green glasses found in New Guinea) were shown to be of probable artificial origin (Visker et aZ 28.105.084). Microtektites in deep-sea sediments cored outside the known limits of tektite strewnfields have been used to extend the boundaries of the Australasian, Ivory Coast and North American tektite strewnfields (Glass et aZ 28.105.150). The North American strewnfield, for example, appears to extend at least halfway around the Earth and contains at least 1011 kg of tektite glass. Mason (1979) found that australites have a more restricted range in composition than micro tektites from deep-sea sediments south and west of Australia and argued against claims for a cornmon origin for australites and microtektites. This position is supported by the suggestion that australites fell only 7000 - 20,000 years ago (Chalmers et aZ 1979). Arguments supporting a time of fall of 700,000 years for the australites and cornmon origin for australites and Indian Ocean microtektites ar.e given by Glass (1979). Recent findings concerning Darwin glass in Tasmania also support a time of fall of 700,000 yrs. (Fudali and Ford, 26.105.060). The argument over the or~g~n of tektites continues. Although some investigators support a lunar volcanic origin (see for example, O'Keefe 28.105.083), most investigators support a terrestrial impact origin. (One author, Crawford, 1979, supports a terrestrial volcanic origin). Calculations indicate that the observed variation in amount of ablation observed on tektites could have been produced at velocities greater than the Earth's escape velocity, if the tektites entered the atmosphere in a swarm (Sepri et aZ 1981). This result is consistent with an extraterrestrial origin for tektites; however, major element composition (Bentor 1979), nitrogen concentrations (Shukla et aZ 1979), and lithium concentrations (Shukla and Goel, 1979) of various tektites all support a terrestrial impact origin. Sm-Nd and Rb-Sr isotopic studies of Australasian tektites (Shaw and Wasserburg 1981), lithium concentrations of various tektites (Shukla and Goel, 1979), and mineral inclusions found in Muong Nong-type tektites from Indochina (Glass and Barlow, 25.105.231) and in Czechoslovakian tektites (moldavites) (Jung and Weiskirchner, 27.022.047) all support a terrestrial sedimentary deposit as the parent material. If tektites were formed by terrestrial impact events, then there should be a crater associated with each strewnfield. The Ries crater in Germany and the Bosumtwi crater in Ghana have been suggested as the source of the moldavites and Ivory Coast tektites, respectively. Trace element studies of the tektites and crater material support this suggestion (Haskin et aZ~ 1980). The impact breccia at the Bosumtwi crater was found to have a normal polarity and this data along with radiometric age data, indicates that the crater was formed during the Jaramillo geomagnetic event (Jones et aZ 1981). This agrees with the observation that the Ivory Coast microtektites are found near the base of the Jaramillo event in cores from the Atlantic Ocean (Glass et aZ 28.105.150). Candidate source craters for the Australasian tektites include a buried crater in Antarctica, an unverified and undated crater in Cambodia (25.081.036),Elgygytgyn crater (Siberia) and Zhamanshin crater (USSR). There is no evidence for the Antarctic crater (Bentley, 26.105.030) and Elgygytgyn crater is too old (Storzer and Wagner, 27.105.158). Irghizites from the Zhamanshin crater are compositionally very similar to some Australasian tektites (Glass, 1979; Taylor and McLennan, 26.105.016; Van Patter et aZ 1981) and the crater and tektites appear to have the same age (Bouska et aZ 1981), but the crater may be too small to be a viable source for the Australasian strewnfield (Taylor and McLennan; Bouska et aZ; Baldwin 1981). A further complication is the suggestion by Storzer and Wagner

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(1980) that the australites are older than other Australasian tektites, indicating that at least two separate events were involved in the formation of the Australasian strewnfield. Possible crater sources for the North American tektites are, Popigai (northern Siberia), Lake Winapitei and Lake Mistanstin (Canada) (Bottomley et al 1979), and an undated crater in South Texas (King, 1979). Storzer and Wagner (27.105.158) suggest that Popigai crater is too young. There is some evidence to suggest that at least three of the four known tektite events were associated with reversals of the Earth's magnetic field (see Glass et al 28.105.150). There is also some data suggesting that extinctions of marine organisms were approximately synchronous with some of the tektite events (Glass et al ·28.105.150). It is speculated that the extinctions may have been caused by climate changes triggered by the tektite events (O'Keefe, 1980).

x

INTERPLANETARY DUST DISTRIBUTION AND DYNAMICS

H. Fechtig.

The main progress in this field originates from three different sources: project Helios, project Pioneer 10/11, and lunar microcraters. Two dust sensors on each of the Helios spacecrafts have scanned between 1 and 0.3 A.U .. One sensor (ecliptic sensor) scans in the ecliptic plane, the other (south sensor) is tilted towards the ecliptic south pole and scans off the ecliptic plane. The two sensors are sensitive to particles in the mass range between 10- 17 and 10-8 g • The time of flight mass spectrometer has only a limited mass resolution of m/~m ~ 5. Both sensors are identical, except that the ecliptic sensor is covered by a 0.4~ thick foil while the south sensor is uncovered. Several hundred particles have been detected by the Helios 1 space probe. The fluxes of particles between 1 and 0.5 A.U. steadily increase with decreasing distance to the sun, although between 0.5 and 0.3 A.U. this increase is less steep. (Gr~n et al, 27.106.016; Pailer and Gr~n, 27.022.118). Concerning the dynamics, the comparison of recordings between the two sensors makes it possible to distinguish between two different types of orbits and particles. Low density particles « 1 g/cm3 ) are orbiting the sun on elliptic orbits (eccentricities> 0.4) while normal density particles remain on quasicircular orbits (eccentricities < 0.4) around the sun. The properties and the orbits of the first class of particles indicates a cometary origin, and one might assume that the second class of particles is of asteroidal origin. However, the Pioneer 10/11 dust experiments did not measure any dust enhancements within the asteroidal belt, and therefore it seems more likely that the "young" cometary particles on elliptical orbits slowly change their structures and become more dense due to thermal influences during perihelion passages. Particles with densities > 1 g/cm3 on quasi-circular orbits are in this sense "old". The meteoroid penetration detectors on Pioneer 10 and 11 consist of pressurized cells covered with stainless steel (25 ~m thickness on Pioneer 10 and 50 ~m on Pioneer 11). A meteoroid penetrating a cell causes a loss of pressure and is thereby recorded. The respective threshold sensitivities are approximately 10-9 g for Pioneer 10 and 10-8 g for Pioneer 11. Earlier publications reported a constant spatial number density of dust particles between 1 and 5 A.U. even within the asteroidal belt with a substantial increase of the dust flux near Jupiter. In a recent publication Humes (28.106.079) reports that the spatial number density of meteoroids is constant even all the way out to 18 A.U. from the sun. Data obtained during the Saturn fly-by of Pioneer 11 shows that within 3.1 Saturnian radii the meteoroid flux increases by 3 orders of magnitude. From a comparison of particles recorded during three scans of the space between 4 and 5 A.U. by Pioneer spacecraft with different attitudes it is concluded that the particles are in randomly inclined orbits of high eccentricity. This implies that the detected particles are on comet-like orbits and proves again

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that comets are the main sources of micro-meteoroids. Some properties of interplanetary dust particles can be inferred from a study of lunar microcraters. These studies refer to the observation that diameter/depth ratios of lunar microcraters only depend on the projectile densities (Brownlee et al (12.094.524); Smith et al (12.094.145); Nagel et al (14.094.181); Nagel and Fechtig (28.022.002). Lamy and Perrin (28.106.030) and Le Sergeant and Lamy (28.106.080, 22.106.058) have investigated the distribution of stony meteoroids versus iron meteoroids as a function of crater and projectile sizes. The general result is that the smaller the crater sizes the greater the proportion of iron meteoroids as compared to stony meteoroids. From these observations the authors identify the sub-micron-sized Smeteoroids with iron projectiles which leave the solar system on hyberbolic orbits. The inward spiralling meteoroids (diameter > 2 ~m) are identified with stony meteoroids. A potential collisional or thermal production mechanism for Smeteoroids close to the sun cannot be supported since the quantities of inspiralling mass and outgoing mass cannot be brought into any quantified agreement. From these two arguments it is concluded that the solar system dust cloud exhibits two fully independent populations: population 1 consists of large grains (diameter> 2 ~m) with densities typical of silicates; population 2 consists of small grains (diameter < 2 ~m) with densities typical of iron. This result, however, is still controversial as the authors have not considered the influence of the so-called a-meteoroids which are produced within 0.5 A.U. of the sun by collisions, but are still large enough to remain on bound orbits until they collide again.

XI

INTERPLANETARY DUST - PHYSICAL CHARACTERISTICS AND SOURCES

D.E. Brownlee.

The sources of interplanetary dust are the interstellar medium and solar system bodies that do not have significant stable atmospheres. The major suppliers are comets and asteroids with comets widely believed to be the dominant source as they are the major producers of the millimeter meteoroids that produce visual meteors. A case has not been made that asteroid collisions are the major dust source but the present understanding of the dust complex is not compatible with known comets being the major source either. Kresak (28.106.032) has estimated that known comets replenish only 1% of the dust lost annually by collisions and Poynting Robertson drag. He suggests that the dust complex may be dominated by material released from rare, large comets. This would produce a dust complex that is only in quasi-equilibrium relative to processes which destroy dust. If this is the case then the spatial density and size distribution of dust should fluctuate significantly on time scales of 104 - 105 years. Sources of dust which are usually minor are ejecta from bodies of planetary size and interstellar grains which transit through the planetary system. Morfill and Gr~n (26.106.009) and Gustafson (26.131.100) discussed the Lorentz effect on small interstellar grains streaming through the solar system. Gustafson showed that if thermal velocities are small relative to streaming velocities, then magnetic focussing effects can produce large density enhancements in certain areas of the solar system and depletions in other regions. Morfill and Gr~n showed that except for favourable solar cycles, focussing and defocussing by the interplanetary magnetic field can prevent particles smaller than 10- 5 em (depending on the charge) from entering the inner regions of the solar system at low latitudes. Tomandl and Berg (21.106.025) measured an upper limit on the flux of interstellar grains at 1 A.U. of 6 x 10-5 m-2 s -1 for masses greater than 2 x 10-14 g . The measurement was made with the LEAM micro-meteorite detector placed on the Moon by Apollo 17. Alexander (25.106.044) discussed processes by which submicron ejecta from lunar impacts could produce enhancement in the near earth dust flux at certain times in the lunar cycle.

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If the orlgln of interplanetary dust is material from comets which formed by accretion of pre-solar interstellar grains, then the dust should have properties compatible with aggregates of interstellar grains. Greenberg (28.106.045, 27.106.010) suggests that the particles would be porous birdnest aggregates of core-mantle interstellar grains; the surviving mantle material would be carbonaceous materials altered by UV and charged particle irradiation in the interstellar medium. New information on the physical properties of dust has been obtained from spacecraft measurements and laboratory analysis of recovered samples. Geise et al (21.106.031, 21.106.051, 28.106.021) conducted microwave analog experiments which suggest that the scattering functions and polarization of the zodiacal light are best reproduced by irregular porous and absorbing particles larger than 10 Wm. Two particle populations for the zodiacal light was discussed by Lamy and Perrin (28.106.030). Evidence that the dust complex is composed of two components distinguished by size and composition was presented by LeSergeant and Lamy (22.106.058) and LeSergeant et al (28.106.080). They indicate that lunar micro crater data on size distribution and crater morphology is consistent with particles > 2 Wm being silicates and particles < 2]lm being metallic fron. This is not compatible with collected sample results but it is a hypothesis that can be tested by' future spacecraft experiments. The spacecraft data from Helios presented by Grun et al (27.106.016) suggest a bimodal population but do not clearly indicate that there is a transition from pure iron to silicate at 2 ]lm. The Helios penetration data indicate that apex particles (fairly circular orbits) have moderate densities while 30% of the particles which have fairly elliptical orbits have densities of < 1 g cm- 3 • Rather extensive laboratory studies have provided detailed information on the properties of micrometeorites recovered from the stratosphere. Hudson et al (1980) measured rare gas contents of several particles proving that the particles are extraterrestrial and that they have probably been exposed to solar wind. The high measured Xe contents suggest that the particles may contain a large "planetary gas" component. Fraundorf et al (28.106.004) performed optical and IR transmission measurements on particles and detected the presence of the ~ 1000 cm- I silicate feature seen in the interstellar medium and in comet dust. Future studies will allow detailed comparison with astronomical sources and laboratory analogs. The isotopic composition of Mg was measured for several particles by Esat et al (26.106.019). The major result was that most particles had a normal isotopic composition at the 1% level althouth one particle was found with a 1.1% mass fractionation and most particles showed a hint of an excess of 26 Mg at a level of ~ 0.4%. Ganapathy et al (26.106.042) measured the trace element compositions of two 50 Wm particles using neutron activation and found them to agree with type I carbonaceous chondrites. Detailed electron microscope studies of particles were described by Fraundorf (28.105.129, 1981), Flynn et al (25.105.173) and Brownlee et al (28.106.044, 22.l06.0I0, 22.106.001). The majority of collected particles are similar to carbonaceous chondrites but they differ in internal structure and mineralogy suggesting that they are a new kind of extra terrestrial material more porous and fragile than conventional meteorites. Atmospheric heating of micro-meteorites which could lead to thermal alteration was discussed by Fraundorf (28.106.071). Deep sea spherules as a source of information on interplanetary dust was discussed by Brownlee (1981). Interpretation of deep sea spherules not as meteor ablation spherules but as rounded bodies created in space was described by Parkin (28.106.076, 22.106.047) and Hughes 28.106.052. A literature review was made by Brownlee (26.106.047) and a popular review by Millman (25.106.072).

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References Aikin, A.C.: 1981, Nature 291, p.638. Arijs, E., Nevejans, D., and Ingels, J.: 1980, Nature 288, p.684. Babadzhanov, P.B. and Zausaev, A.F.: 1980, Bull. Astron. Inst. Akad. Nauk Tadjikistan, No. 69-70, p.54. Babadzhanov, P.B., Zausaev, A.F. and Obrubov, Yu.: 1980, Bull. Astron. Inst. Akad. Nauk Tadjikistan, No. 69-70, p.45. Baggaley, W.J.: 1978, Nature 274, p.624. Baggaley, W.J.: 1979a, Planet. Space Sci. 27, p.533. Baggaley, W.J.: 1979b, Planet. Space Sci. 27, p.1131. Baggaley, W.J.: 1980a, The Observatory 101, p.9. Baggaley, W.J.: 1981a, Bull. Astron. Inst. Czech. 33, in press. Baggaley, W.J.: 1981b, Nature 289, p.530. Baggaley, W.J. and Webb, T.H.: 1980, Planet. Space Sci. 28, p.997. Baldwin, R.B.: 1981, Icarus 45, p.554. Becher, H.J.: 1980, Sterne und Weltraum, No.6, p.222. Bedard, A.J.Jr. and Green, G.E.: 1981, J. Acoust. Soc. 69, p.1277. Bennett, J.C.: 1978, Monthly Notes Astron. Soc. S. Africa 37, p.85. Bentor, Y. K.: 1979, Trans. Am. Geophys. Union 60, p.870. Biberman, L.M., Bronin, S.Ya. and Brykin, M.V.: 1980, Acta Astronautica 7, p.53. Bottomley, R. J.: 1979, Trans. Am. Geophys. Union 60, p.309. Bouska,V.I., Povondra,P., Florenkij,P.V., Randa,Z.: 1981, Meteoritics 16, p.171. Brownlee, D.E.: 1981, in The Sea, Vol. 7, ed. C. Emiliani, Wiley. Ceplecha, Z.: 1967, Bull. Astron. Inst. Czech. 18, p.233. Ceplecha, Z.: 1981 SEAN Bull. 6, No.2, p.15. Ceplecha, Z. and McCrosky, R.E.: 1976, J. Geophys. Res. 81, p.6257. Ceplecha Z. Bocek, J., Novakova, M., Kirsten, I. and Kiko, J.: 1982, Bull. Astron. Inst. Czech. 33, in press. Chalmers, R.O., Henderson, E.P., Mason, B.: 1979, Bull. Geol. Soc. Am. 89, p.1455. Cook, A.F. and Duxbury, T.C.: 1981, J. Geophys. Res., in press. Crawford, A.R.: 1979, Geol. Mag. 116, p.261. Dmitrievskij, A.A.: Astron. Vestn. 14, p.230. Drummond, J.D.: 1981, Icarus 48, p.545. Dubin, M.: 1981, EOS (Trans. Amer. Geophys. Union), 62, p.321 (Abs). Ferguson, E.E., Rowe, B.R. Fahey, D.W. and Fehsenfeld, F.C.: 1981, Planet. Space Sci. 29, p.479. Fraundorf, P.: 1981, Geochim. Cosmochim. Acta 45, p.915. Gadsden, M.: 1978, J. Geophys. Res. 83, p.1155. Glass, B.P.: 1979, Geology 7,351. Hajduk, A. and Cevolani, G.: 1981, Bull. Astron. Inst. Czech., in press. Hajdukova, M., and Hajduk, A.: 1981, Astron. et Geophys. 6, p.15. Halliday, I., Griffin, A.A. and Blackwell, A.T.: 1981 Meteoritics 16, p.1S3. Halliday, I. and Griffin, A.A.: 1981, Meteoritics 16, in press. Haskin, L.: 1980, Lunar Planet. Sci. Conf. XI, p.410. Herrmann, U., Eberhardt, P., Hidalgo, M.A., Kopp, E. and Smith, L.G.: 1978, Space Res. 18, p. 249. Hudson, B., Flynn, G.J., Fraundorf, P., Hohenberg, C.M. and Shirek, J.: 1980, Science 211, p.383. Hughes, D.W., Williams, I.P. and Fox, K.: 1981, MNRAS, 195, p.625. Hunten, D.M., Turco, R.P. and Toon, O.B.: 1980, J. Atmos. Sci. 37, p.1342. Jones, J. and Morton, J.D.: 1981, Monthly Notices Roy. Astron. Soc., in press. Jones, W.B., Bacon, M. and Hastings, D.A.: 1981, Bul!. Geo!. Soc. Am. 92, p.342. Kalchenko, B.V. and Kashcheyev, B.L.: 1981, Meteor Researches 7, p.S. Kazantzev, A.M. and Sherbaum, L.M.: 1981, Probl. kosm. phys. 16, p.30. Kerker, M.: 1981, Planet. Space Sci. 29, p.127. King, E. A.: 1979, Geology 7, p.328. Kovshun, LN. and Smirnov, V.A.: 1978, Astron. Vestn. 12, p.199. Kramer, E.N., Markina, A.K. and Shestaka, I.S.: 1980, Astron. Vestn. 14, p.202.

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Kramer, E.N., Musiji, V.l. and Shestaka, I.S.: 1980, Akad. Nauk Tadjikistan SSR, Komety i Meteory, No. 29-31, p.83. Kramer, E.N. and Shestaka, I.S.: 1977, Astron. Vestn. 11, p.:'2.6. Kramer, E.N. and Shestaka, I.S.: 1981, Comet Circ. USSR 274, p.4. Kramer, E.N. and Timczenko, E.A.: 1981, Astron. Vestn. 15, p.50. Lebedinets, V.N.: 1981, Astron. Vestn. 15, p.36. Levitsky, S.M. and Abdrakhmanov, N.: 1978, Geomag. Aeronomy 18, p.497. Liu, S.C. and Reid, G.C.: 1979, Geophys. Res. Lett. 6, p.283. Mason, B.: 1979, Smith. Contr. Earth Sciences, No. 22, p.14. McIntosh, B.A. and Hajduka, A.: 1977, Bull. Astron. lnst. Czech. 28, p.280. McLeod, N.W.: 1981, Sky and Telescope 61, p.502. Megie, G. and Blamont, J.E.: 1977, Planet Space Sci. 25, p.1093. Murad, E. and Swider, W.: 1979, Geophys. Res. Lett. 6, p.929. Nevskii, A.P.: 1979, Sol. Sys. Res. 12, p.173. Novakova, H.: 1979, Sterne und Weltraum, No. 11, p.382. Novakova, H.: 1981, Sterne und Weltraum, No. 6-7 p.254. Novikov, G.G., Tzigankov, S.F. and Blokhin, A.V.: 1981, Geomag. Aeron. 21, p.105. O'Keefe, J.A.: 1980, Nature 285, p.301. Pecina, P. and Ceplecha, Z.: 1982, Bull. Astron. lnst. Czech. 33, in press. Perry, R.A., Rowe, B.R., Viggiano, A.A., Albritton, D.L., Ferguson, E.E. and Fehsenfeld, F.C.: 1980, Geophys. Res. Lett. 7, p.693. Petrov, G.I. and Stulov, V.P.: 1975, Cosmic Res. 13, p.525. Polnitzky, G.: 1981 SEAN Bull. 6, No.5, p.15 •. Poole, L.M.G.: 1978, Nature 274, p.624. Poulter, E.M.: 1980, J. Atmos. Terr. Phys. 42, p.69. ReVelle, D.O.: 1981a, 1981b, J. Geophys. Res., in press. Richter, E.S. and Sechrist, C.F.: 1979, Geophys. Res. Lett. 6, p.183. Richter, E.S. Rowlett, J.R., Gardner, C.S. and Sechrist, C.F.: 1981, J. Atmos. Terr. Phys. 43, p.327. Russell, J.A.: 1980, Meteoritics 15, p.361. Saidov,K.Kh. and Zolova,O.F.: 1980, Bull. Astrophys. lnst., Dushanbe 69-70, p.7l. Sepri, P., Chen, K.K. and O'Keefe, J.A.: 1981, J. Geophys. Res. 86, p.5103. Shaw, H.F. and Wasserburg, G.J.: 1981, Lunar Planet. Sci. Conf. XII. Sherbaum, L.M. and Kazantzev, A.M.: 1980, Vestn. Kiev. Univ. 22, p.61. Shukla, P.N, and Goel, P.S.: 1979, Geochim. Cosmochim. Acta 43, p.1865. Simek, M. and Hajduk, A.: 1981, Bull. Astron. lnst. Czech. 32, p.120. Simonenko, A.N., Kruchinenko, V.G. and Sherbaum, L.M.: 1980, Meteoritika 39, p.121. Storzer, D, and Wagner, G.A.: 1980, Naturwiss. 67, p.90. Tkachuk, A.A.: 1978, Meteor Researches 5, p.67. Tkachuk, A.A.: 1981, Meteor Researches 7, p.28. Tkachuk, A.A. and Matsenko, S.V.: 1981, Meteor Researches 7, p.63. Turco, R.P., Toon, O.B., Hamil, P. and Whitten, R.C.: 1981, JGR, 86, p.1113. Van Patter,D.M., Swann,C.P. and Glass,B.P.:1981, Geochim Cosmochim Acta 45, p.229. Voloschuk, Yu.l. and Kashcheyev, B.L.: 1981, Nauka, Moscow. Voloschuk,Yu.I., Kashcheyev,B.L. and Tkachuck,A.A.:1981a, Astron. Vest. 15, p.125. Voloschuk, Yu.l., Kashcheyev, B.L. and Tkachuck, A.A.: 1981b, Astron. Vestn. 15, No. 3 and No.4. Webb, T.H.: 1981, Planet. Space Sci. 29, p.415. Weeks, R.A., Nasrallah, M., Arafa, S. and ~ishay, A.: 1980, J. Non-Crystalline Solids 38 and 39, p.129. Wetherill, G.W. and ReVelle, D.O.: 1981, Icarus, in press. Wood, J.: 1981, British Meteor Soc. 11, p.71. Yabuki,H., Shima,M. and Yabuki,S.:1981j Sci. Pps. lnst. Phys. Chern. Res. 75, p.41. Znojil, V., Simek, M., Grygar, J. and Hollan, J.: 1981, Bull. Astron. lnst. Czech. 32, p.1. W.G. ELFORD President of the Commission

24. PRESIDENT:

PHOTOGRAPHIC ASTROMETRY (ASTROMETRIE PHOTOGRAPHIQE)

Heinrich Eichhorn

VICE PRESIDENT:

Wilhelm Gliese

ORGANIZING COMMITTEE:

Ch. de Vegt, L.W. Frederick, G. Gatewood, R.S. Harrington, C.A. Murray, H.I. Potter, A. Upgren.

I. INTRODUCTORY REMARKS The name of this commission was recently changed from "Parallaxes and Proper Motions". These data are at this time indeed obtained mostly by the techniques of photographic astrometry, but so is the bulk of relative star positions. It is clear, however, that the nonabsolute determination of relative positions and data derived from them in narrow fields (which describes the scope of this Commission) is going to be carried out more and more also by nonphotographic methods, namely photoelectrically (Earth and satellite based) by interferometry (optical, radio, and speckle) and by direct imaging. This therefore creates considerable overlap with the subject areas and methods of a number of other Commissions, especially Commission 8, and it will be appropriate for Commission 24 in the near future to examine critically the overlapping areas of interest and to come to an agreement about the definition of the proper responsibilities of the individual commissions. II.

TECHNIQUES

a) Satellite based astrometry Astrometry from satellites is actively planned in the US (Space Telescope) and in Europe (HIPPARCOS). No data have yet been obtained; the work being done at present is mostly the development of the software for the reduction of the observations, note in particular the papers by Jefferys (AJ 84, 1775, 1979; AJ 85, 177, 1980). The papers collected in the conference on European Satellite Astrometry (25.12.060) as well as some published in the proceedings of IAU colloquium No. 48, Modern Astrometry, (25.12.0181) give good overviews over these plans which will therefore not be repeated in this report. b) Non-photographic small field differential astrometry Lindegren (IAU ColI. No. 48, Modern Astrometry, 197, 1979) gives a survey of the mathematical techniques for computing the position of objects by photoelectric methods. A team led by Gatewood at the Allegheny Observatory reports near completion of a multi-channel astrometric photometer, (MAP) a photoelectric device which is intended to perform photoelectrically the tasks traditionally performed by long focus photographic astrometric techniques. Gains in precision of about two orders of magnitudes are expected. (see, e.g., Icarus 41, 205, 1980). Connes (cf. Eur. Sat. Astrom. 157, 1979) has been advocating a ground based photoelectric device for single target differential astrometry - i.e., parallax and perturbation studies - which uses custom masks for each region. c) Interferometry Routine speckle interferometric measurements of double stars have successfully been carried out for years and are reported on elsewhere. Systems for making ground based optical interferometric measurements within the realm of single tar237

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get differential astrometry have been proposed (Shao, Curry) but are not yet operational. d) Fully automatic measurements of photographic plates Previously unreported developments concern microdensitometers, described in analyses by Richter (AN 299, 283, 1978), and Auer and van Altena (AJ 83, 531, 1978). e) Reduction technique Astrometry is one of the prime areas for the application of sophisticated data adjustment techniques. Papers on least squares adjustment besides those published by Jefferys referred to above (IIa) were reported by Branham (AJ 85, 1520, 1980), Eichhorn (MNRAS 182, 355, 1978), Fresneau (AJ 84, 244, 1979) and von der Heide (AA Supp. 32, 141, 1978). Papers directly concerned with the reduction of measurements made on photographic plates were published by Fresneau (AJ 83, 406, 1978), von der Heide (AA 72, 324, 1979) and Wayman (Irish AJ , 13, 226, 1978). III.

DATA

a) Parallaxes (i) Parallaxes of individual objects were published by Armbruster (PASP 90, 219, 1978 - ADS 8887), Hershey (AJ 83, 308, 1978 - G24-16), Hershey (AJ 83, 197, 1978 van Maanen's star), Kamper and Wesselink (AJ 83, 1653, 1978 - a and Proxima Cen.) Kipp and al. (AJ 83, 636, 1978 - 45 Tau., 97 Tau, 102 Tau, 31 Cyg and other stars in the region), Pannunzio (Mem. Soc. Astr. Ital. 51, 137, 1980 - Stein 2051), Russell and al. (AJ 83, 1455, 1978 - Altair), Russell and Kipp (AJ 83, 305, 1978 18'Puppis, BD+4001847, Lalande 26325, G137-8 and selected reference stars) and Salter and al. (Nature 280, 477, 1979 - pulsars). (ii) Published lists of newly measured parallaxes include the following: Auer et al. (AJ 83, 640, 1978), Harrington and Dahn (AJ 85, 454, 1980), Hershey (AJ 83, 1119, 1978) Ianna (AJ 84, 127, 1979), Scales (MNRAS 184, 101, 1978). Upgren and Breakiron (AJ 85, 71, 1980) and Vilkki (AJ 83, 978, 1978). (iii) Among papers concerning parallaxes were those by Halliwell (AJ 24, 259 and 273, 1980 - research priorities), Hershey (AJ 85, 1399, 1980 - astrometric analysis of 14 Sproul series), Lutz (IAU ColI. No. 48, 7, 1979 - statistics and parallaxes), Murray and Corben (MNRAS 187, 723, 1979; 900 parallaxes and proper motions near the South Galactic Pole determined with the UK Schmidt telescopes [methods and first results]) and Upgren and Lutz (Dudley Obs. Rept. No. 14, 235, 1979 - The influence of parallax errors on photometric calibration), Lippincott and Hershey (AJ 84, 567, 1979), Hanson (MNRAS 192, 347, 1980), and Lutz and Upgren (AJ 85, 1390, 1980). b) Proper Motions (i) Papers published on proper motion programs include one by Klemola (IAU ColI. No. 48, 387, 1979 - Lick program) and one by Rakhimov (Tr. Astr. Inst., Tashkent Vol. 2, 59, 1978 - on the Tashkent catalogue of proper motions with reference to Galaxies). Eggen (ApJ Supp. 39, 89, 1979) published photometric data for stars brighter than 15m whose proger motion exceeds I"/yr., and in (ApJ Supp. 43, 457, 1980) the data for stars l because of tile much deeper potential well of this compact star. B. The Magnetic Accretion Model. If the white dwarf has a magnetic field strong

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enough to channel the accreting matter, the spectral distribution will be substantially altered from the steady disk picture (29,30,21). In this case the accretion flow is pseudo-radial and a strong shock is formed in the accretion column at a distance above the stellar surface that depends on the velocity of the flow and the cooling rate of the falling gas. In the hot, post-shock emission region the electrons will be cooled through both bremsstrahlung and cyclotron interactions. About one-half of the flux in this region is emitted outwards, either as bremsstrahlung emitted at hard X-ray wavelengths, or blackbody-limited cyclotron radiation at longer wavelengths (i.e., in the VV, optical or infrared, depending on the value of the magnetic field strength, B, the mass accretion rate, m, and the mass of the accreting star, M). The competition between bremsstrahlung and cyclotron radiation is determined by m and B. At high accretion rates or low magnetic field strength, bremsstrahlung dominates, but at low accretion rates or high field strength, the balance shifts toward cyclotron cooling. The other half of the radiation emitted in the post-shock region is absorbed by the surface of the degenerate star, producing a blackbody component which has an effective temperature around a few xl0 5K. Conduction of energy by electrons may also heat t;le stellar surface (32). For large enough m and/or B the blackbody component may be observable at soft X-ray wavelengths. Additional contributions to the UV and visible may result from emission from falling material (above the shock) that is heated by Compton scattering or cyclotron absorption (33,34). The Observations. A. Dwarf Novae in Quiescence. Recent observations at high energies suggest that the dwarf novae are accreting at very low rates between outbursts. Therefore, sources of luminosity other than the disk, such as the component stars or the mass transfer region on the outer disk, may dominate the UV + optical +IR continuum. In two 'dwarf novae, SS Cyg and V Gem, a A- 4 component is detected in the far VV (35); this radiation may be from a very hot white dwarf whose EVV emission greatly exceeds the combined VV and optical emission, or from a very small, hot disk. In any case, it is difficult to estimate the luminosity of this component from the low-energy tail of the spectrum alone. In three other dwarf novae (AH Her, YZ Cnc, and SV UMa) the far UV distribution does not differ appreciably from the A- 2 . 33 slope of a steady disk, but the distribution longward of 2200 A is flatter (i.e. falls less steeply with wavelength) than a steady disk spectrum (36). This may be due to the contribution of the "bright spot" where the mass stream impact the outer disk (e.g. in (9) a 10,000 K blackbody is fit to a phase-dependent component associated with the bright spot of V Gem). EX Hya is, to date, the only dwarf nova inquiescence which seems to fit the steady disk model from 1200 A to 2.2).l (23,37) (and this star may be a rather exotic "dwarf nova"; see later discussion). Most dwarf novae in quiescence do not lie in the steady disk region of the V-B, B-V (colour/colour) diagram (38). "Hard" X-ray emission (kT eff >2 keV) has been detected from 70% of the more than 70 CVs observed at high energies (9). It is thought that this emission comes from the inner region of the disk because of its high temperature (~10 keV (49» and because of the observation of a hard X-ray eclipse coincident with the optical eclipse of HT Cas (12). The ratio of hard X-ray flux, fhx, to the visual flux, fv (5000-6000 A), is of order unity for the dwarf novae in quiescence (39,12). This is the highest ratio exhibited by any class of nonmagnetic CV. The hard X-ray luminosity in some of these systems (e.g. EX Hya, SS Cyg, HT Cas) is comparable to the combined VV+ optical disk luminosity (23,39,12,36). This implies, according to the disk model discussed in Section IIa, that the boundary layer emission is optically thin, and hence the accretion rate is low (M1.5Me. Nor are non-Ha emission stars rapid rotators unless their mass >1.5Ms . The break in rotational velocity found for main sequence stars is therefore already present as soon as the stars appear with a photospheric spectrum. The angular momentum problem must also have been solved before we see the stars. Vogel and Kuhi also showed that the Skumanich relation could be made to hold for pre-Main Sequence stars if the angular momentum were used in place of the surface rotational velocity. This would allow changes in the internal density distribution to be taken into account. They further speculate that the rapid rotators may be found among the strong-line stars for which no photospheric lines are visible. The upper limits still allow considerable braking to take place via stellar winds during subsequent evolution but at mass loss rates well below detectable levels. The continuous emission from the surroundings of T Tauri stars has been studied at radio frequencies by Bertout (in press) and Cohen anJ Bieging (ApJ in press). The radio emission is ascribed to free-free emission from a hot gas which is very likely aspherical in distribution according to the latter authors. This free-free emission is also detected at infrared wavelengths for many T Tauri stars but Cohen and Kuhi (ApJ Suppl 41.743) used infrared colour indices to show that for most stars the infrared energy distribution was likely due to thermal reemission from circumstellar dust. Rydgren and Vrba (AJ 86.1069) have confirmed this conclusion. A survey for circumste1lar OH emission was carried out by Gahm et al. (AA 83.263) who found no such emission clearly associated with T Tauri stars hence confirming earlier negative results. Extensive polarization measurements have been carried out by Bastien and Landstreet (ApJ Lett 229.L137) and Bastien (AA 94.294) who conclude that most of the polarization must be produced by circumstellar dust envelopes lying outside the emission-line producing region. Bastien interprets the variations in the wavelength depenJence of polarization as due to variations in dust grain size, i.e. consistent ~60

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with the idea of grain formation amound T Tauri stars. We also note Walker's (PASP 92.66) observations of the spectral and light variations of BM And. No spectral change correlated with light variation occurs and Walker concludes that the light variations must be due to variable extinction produceu by material close to the star, perhaps of protoplanetary origin. Thus BM And joins a growing list of such objects with possible protop1anets. Finally, we note that discussion of various aspects of T Tauri emission and their interpretation are to be found in the proceedings of the symposium "Stellar Physics and Evolution" held in 1979 in Byurakan (edited by Mirzoyan). J.D. Fernie

28. GALAXIES (GALAXIES) PRESIDENT: B.E. Westerlund VICE-PRESIDENT: V.C. Rubin ORGANIZING COMMITTEE. H.C. Arp, E.A. Dibaj, J.A. Graham, J. Heidmann. P.W. Hodge, B.E. Markarian, M. Peimbert, G.A. Tammann, M.H. Ulrich, P.C. van der Kruit. The present report covers the period 1979-1981. As with previous reports it has not been possible to write an all- inclusive account covering everything published, or even every field under investigation; the number of contributions to extragalactic research is increasing faster every year. Summaries of the papers may be found in the Astronomy and Astrophysics Abstracts. The report is divided into ten sections, including the four Working Groups, and they have been prepared by the President, the Vice- President, members of the Organizing Committee and the Chairmen of the Working Groups. References are mostly given by commonly used abbreviations for journals with volume and page numbers but without the year of pUblication; in some sections references by the numbers in the above-mentioned Abstracts have been used. Numerous colloquia and symposia on extragalactic astronomy have been held during the past three years, and proceedings of some meetings held previously have appeared in print. Those referred to in the report of 1979 will notbe repeated here. IAU Symposium No. 92, on "Objects of High Redshifts", covered recent observations of objects of cosmologically significant redshifts. The investigations presented dealt with the whole spectral range, from X-rays to radio wavelengths. IAU Colloquium No. 54, on "Scientific Research with the Space Telescope", had papers dealing with the physical properties of galaxies and quasars. IAU Symposium No.94, on, "Origin of Cosmic Rays", included topics dealing with the nuclei of galaxies, compact and extended radio sources, and the distribution of non-thermal emission in galaxies. IAU Symposium No. 96, on "Infrared-Astronomy" had presentations of infrared studies of galaxy nuclei, Seyfert galaxies, quasars and cosmology. IAU Symposium No. 97, on "Extragalactic Radio Sources", dealt with extended radio sources, various types of structures in sources, QSOs and compact radio sources, and the space distribution and evolution of these objects. A conference was held in Austin, Texas, on "Photometry, kinematics and dynamics of galaxies", before the IAU General Assembly in Montreal. The Highlights of Astronomy, vol. 5, contains the Joint Discussions in Montreal: "Nuclei of normal galaxies" and "Extragalactic high energy astrophysics". The Fifth European Regional Meeting in Astronomy, in Liege 1980, dealt with "Variability in stars and galaxies". 303

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A NORDITA Symposium in Copenhagen 1980, discussed "The universe at large redshifts" (Phys. Sc'r. 21, 599). A discussion of "The origin and early evolution of the galaxies" was organized by McCrea and Rees in 1979 (Phil. Trans. Roy. Soc. London, Ser. A, 296,269). Conferences and Workshops organized jointly by ESA and ESO dealt with "Optical jets in galaxies" (ESA SP-162), "Dwarf galaxies" (ESO Report), and Astronomical uses of the Space Telescope". An ESO Workshop on "Two Dimensional Photometry" has sections on extragalactic photometry. Proceedings have appeared from the "Pittsburgh Conference on BL Lac objects" (Univ. of Pittsburgh), the NATO Advanced Study Institute on "Active galactic nuclei", and the Cospar Symposium on "X-ray astronomy". Among important review papers to appear during the period under consideration are: Masses and mass-to-light ratios of galaxies (Ann.Rev.Astron.Astrophys. 17, 135); Globular clusters in galaxies (ibid.17, 241); Infrared emission of extragalactic sources (ibid.17,477); The structure of extended extragalactic radio sources (ibid.18,165); Optical and infrared polarization of active extragalactic objects (ibid.18, 321); Absorption lines in the spectra of quasistellar objects (ibid. 19, 41); Abundances in stellar population and the interstellar medium in galaxies (ibid. 19, 77); The extragalactic distance scale (ibid. 19, 357); Compact radio sources (ibid.19, 373); The emission lines of quasars and similar objects (Rev. Mod.Phys. 51, 715), and "The discovery and observed properties of QSOs at large redshifts- and update"(M.G.Smith, preprint, for publ. in "Investigating the Universe", ed. F.D. Kahn). A number of reviews have appeared in Comments on Astrophysics and in Science. 1. GALAXIES IN GENERAL (B.E. Westerlund) A. Survey work; Catalogues The ESO/Uppsala "Quick Blue Survey" of the southern hemisphere is completed: lists nos. 7, 8 and 9 are published (AA Suppl 39, 173; 43, 307; 46, 311). In all, 606 fields south of decl.- 17?5 have been investigated and about 16 000 galaxies and physically connected systems recorded, with total diameter ~ 1.0 arcmin. An updated, cross-checked version of the catalogue is being prepared and will become available in computer readable form at the end of 1981. It will also contain B mag, B-V colours and redshifts for about 2 000 Galaxies. The survey of southern galaxies (6 10 41 ergs s-1) which have been identified and for which redshifts have been measured. "An update of the status of the Revised 3C Catalog of radio sources" (PASP 92, 553) contains optical positions, redshifts, magnitudes, and identifications as well as radio flux densities and spectral indices for a sample of 297 extragalactic 3C sources. "A revised optical catalogue of quasi-stellar objects" (ApJ Suppl 43, 57) contains the basic information on all QSOs and BL Lac objects which have been certainly identified, a total of 1549 objects. "A catalogue of polarization measurements and related data of extragalactic radio sources" (Acta Cosmol 9,7) gives mainly radio data but also some optical for a total of 510 extragalactic radio sources. "A Catalogue of linear polarization of radio sources" contains all the data of linear polarization of radio sources published prior to December 1978 (AA Suppl 39, 379). Tabara and Inoue report that the catalogue contains 7225 data for 1510 radio sources. Optical data are source identification, optical magnitude, redshift. "A master list of nonstellar optical astronomical objects" contains 185 000 listings from all known catalogues of nonstellar objects and gives 1950.0 position, angular diameter, magnitude and description (Dixon and Sonneborn, Ohio State Univ Press). B. Classification Revised galaxy types are estimated for 153 southern systems in "The las Campanas survey of bright southern galaxies"(AJ 84, 472). Estimates of luminosity class are included and effects of environment on galactic forms are looked for. A new class of amorphous galaxies is introduced, replacing the now abandoned Irr II type. The purpose of the survey was to reclassify the southern Shapley- Ames galaxies. "A revised Shapley- Ames Catalog of bright galaxies" has now appeared (Sandage, Tammann, Carnegie Inst of Wash). It contains newly estimated types and luminosity classes for 1246 galaxies together with other information (See section 5)

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"A catalogue of morphological types in 55 rich clusters of galaxies" (ApJ Suppl 42, 565) gives positions, morphological types, total magnitudes, bulge sizes, and ellipticities for about 6 000 galaxies, as determined from high-scale photographic plates. De Vaucouleurs reports that a catalogue of "Diameters of nuclei, lenses, and inner and outer rings in 512 galaxies" has been published (AJ 85, 637). The measurements have been made on large-scale reflector plates for statistical studies of quantitative galaxy, morphology as well as for other applications. For the determination of the local value of the Hubble constant a luminosity classification on the DDO system for 670 Sb galaxies was carried out (AJ 85, 101). C. Measurements in the Radio Region. Many important catalogues of radio sources have been presented recently. The "Molonglo reference catalogue of radio sources" (MN 194, 693) lists 12 141 sources with 1950.0 positions, 408 MHz flux densities, source types and cross references. The 14th part of the Parkes 2 700 MHz survey (Austr. JPh, Ap Suppl No 46,1) gives data for 278 sources and includes results of examination of the Palomar Sky Survey prints for indentification. A catalogue has been presented (AA Suppl 40, 91) of sources belonging to either or both of two samples complete to 3.7 Jy at 178 MHz and 2.2 Jy at 408 MHz, respectively. The best available information on radio structure, radio spectr~, and optical identification is given. A statistical analysis has been carried out. A confusion- limited 4.755 GHz survey covering 0.00956 sr between 7h 05 m and 18h near decl + 35 0 has been made with the NRAO 91-m telescope (AJ 85, 780) 237 sources were found down to 15 mJy. The material has been extensively analyzed. A number of studies of bright galaxies has been carried out, often resulting in detailed radio maps. Thus, for exemple, 91 spiral galaxies from the UGCG have been observed at 408 MHz with the Bologna Northern Cross Radio Telescope (AA Suppl 41, 329); the sample is complete down to m = 12 mag for the declination zone +20 0 to + 60 0 pg With the Effelsberg 100 m telescope 1616 galaxies from the RCBG and the UGCG were observed at 11 cm (MN 192, 635); 296 radio sources were detected within 2.5 arcmin of the centres of 323 galaxies. Individual detection limits are given for the 1293 undetected objects. - With the same telescope 141 optically bright galaxies were observed at 10.69 GHz; 68 were detected (AA Suppl 41, 151). The radio continuum radiation at 1415 MHz was observed with the Westerbork Synthesis Radio Telescope of 450 galaxies (AA Suppl 41, 151); 190 objects were detected. The limit for point sources was 10 mJy and the resolution about 24 arcsec. - With the same telescope observations were made at 6 cm and 21 cm of a complete sample of sources from the NRAO - Bonn "s4" survey at 5 GHz that have flat highfrequency spectra and are identified with galaxies (AA 74, LII). Most of the brighter galaxies in the survey appear to be related to BL Lac objects. High-resolution maps of all spirals with a radio-to-optical luminosity ratio R > 50 from the Arecibo 2380 MHz survey were made with the NRAO Very Large Array (VLA) at 4885 MHz (ApJ 242, 894). 7 of the 8 objects contained dominant central radio sources with no evidence for enhanced disk emission. 3 of the 7 have flat radio spectra; they are compact « 1 pc) synchrotron self-absorbed radio sources. All of the steep-spectrum sources-were resolved with the VLA with typical sizes of 'V 1 kpc.

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A continuum radio survey at 5 GHz with the NRAO 91 m telescope of all the isolated galaxies drawn from the Zwicky catalogue by Karachentseva and classified E or SO, and spirals between + 10 0 and + 60 0 declination, showed that both the ellipticals and the spirals are extremely deficient in radio sources (AJ 85,1010). A clear correlation is found between frequency of radio emission and local galaxy density, suggesting that gas falling in to a galaxy triggers radio emission. A huge number of neutral hydrogen studies has been carried out for all types of galaxies. Thus an extensive mapping program with the Green Bank 91-m telescope gives the HI line radiation in and around 61 relatively nearby galaxies with diameters between 9 and 36 arcmin (AA Suppl 41, 189). Individual galaxies for which the HI observations have served to determine the internal motions,may be found in the table in section 9. References to neutral hydrogen studies are also found in sections 2, 3 and 5. Evidence for warps in the gas layers of galaxies was found some years ago; a review appears in lAD Symp. No.84, 501. More recent studies of the HI distribution in galaxies has led to substantial warps being found in e.g. NGC 300 (ApJ 229, 509); NGC 3718 (MN 186,343); NGC 4565 (AA 89,95); and IC 10 (MN 187,839). It is noted that NGC 300 has massive HI companions, that NGC 3718 may have had a gravitational encounter with NGC 3729, and that IC 10 may have a chaotic distribution of HI clouds around it. The dynamics of warps in disks is being studied by J.W-K. Mark. He has found that the bending of galaxy disks is unstable in the presence of the more slowly rotating spheroidal subsystem. Analyses of the mechanism and related effects may be found in (AA 88,289; Nature 287,705; ibid 290,120). The asymmetry of the HI distribution in a number of spiral galaxies is analyzed in (MN 193,313). It is proposed that the "lopsided" distribution may be associated with a pattern of elliptical orbits. As most of the galaxies analyzed are rather isolated on the sky the asymmetries are hardly transient phenomena. Among new molecules detected in extragalactic systems we note NHl, at 1,~ ce, in IC 342 and NGC 253 (AA 74, L7), and CH, at 3264 MHz, in the Large Magellanic Cloud, NGC 4945 and NGC 5128 (MN 190, 17P). Most of the search for molecules in extragalactic systems appears otherwise to have been for CO (AA 78, L1; 82, 381; ApJ 240, 60; 240,455) and H20 (Nature 278,34; AA 91, 259). For further investigations in the radio region the reader lS referred to the Report of Commission 40. D. Measurements in the X-ray reglon Among the many pUblications on extragalactic X-ray sources we mention here the Proceedings from the AAS High Energy Astrophysics Division meeting on "X-ray astronomy with the Einstein satellite" and a review "The Einstein Observatory: New Perspectives in Astronomy" (Science 209, 865). X-ray observations are also referred to in several of the 'following sections of our report; they are frequently concerned with active galaxies. X-ray emission from elliptical galaxies has been observed; ~~is may be considered as evidence for the accumulation of extensive gaseous envelopes (HN 192, 135). Normal galaxies may in fact contribute substantially to the diffuse background (Nature 281, 127). For further investigations in the X-ray region the reader lS also referred to the Reports of Commissions 44 and 48. E. Deep galaxy samples and the luminosity function A number of complete samples of galaxies to faint limiting magnitudes have been presented: Fields near the South Galactic Pole have been studied to B ~ 22 mag

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(MN 186,69; 193, 1; Aph Space Sci 72, 315); more than 28 000 galaxies were counted in the field of 15 square degrees. In two high-latitude fields, each of 1080 arcmin 2 , counts to below B = 24 mag have been carried out; about 20 000 galaxies were identified (ApJ Suppl 43,305; Phys Scr. 21,652). Electronograms taken with the 6-m telescope have permitted counts to 25th apparent magnitude (Pis~ma AZh 6,3). In a high-latitude field (b=-65°) observed with the prime focus camera of the AngloAustralian Telescope on IIIa-J plates a limiting magnitude of about 25 was reache~2 (ApJ 233, Ll09). To J o = 24 mag the integrated galaxy surface density was n800deg. Tyson reports on a new technique for detecting and classifying images on astronomical plates (AJ 86, 476). Among the results derived are counts to J = 24 mag (IIIa-J plates) at the North Galactic Pole, giving 17 100 galaxies per deg 2 to this limit (ApJ 230, L153), and permitting a comparison with evolutionary models. The conclusions drawn in most of the papers from the counts of the very fai~t galaxies are that no or only a very moderate amount of galaxy llL':linosity evolution lS seen. The population becomes bluer with increasing faintness. The luminosity function of nearby galaxies (within 10 Mpc) has been investigated by K.-H. Schmidt (AN 302,61). A large population of faint elliptical systems may exist and form an important constituent of the universe. The luminosity function of field galaxies follows the Schechter function well (AJ 84,951); it does not differ significantly from the cluster galaxy luminosity function. The luminosity function of radio galaxies has been studied (ApJ 229,25). No difference in it was found for z < 0.1 and z > 0.1; this is consistent with neither luminosity nor density evolution in the recent past. The slope of the luminosity function of galaxies in Zwicky~s catalogue has been scrutinized (Acta Astr 29,293). It was found to be unstable in the brighter part, to be approximately 0.6 in the intermediate magnitude interval and to be greater than 0.6 in the faintest interval studied (14.7 - m - 15.7). F. Dwarf galaxies The dwarf galaxies in the Local System as well as at greater distances have attracted much interest. The Draco dwarf galaxy has been carefully investigated by Stetson (AJ 84, 1149; 1167; 85, 387), who concluded (AJ 85, 398) that the galaxy may be considered as having one metallicity and an age younger than that of globular clusters. Zinn (AJ 85, 1468) confirmed his previous conclusions that Draco shows a significant dispersion in metallicity. The case for an abundance spread appears good and is upheld by Kinman et al.(AJ 85,414; Phys. Proc. Red Giants,p.71). The structure of the Sculptor dwarf galaxy has been examined by star counts (AJ 85,1587); a tidal radius of 75~is indicated. A tidal analysis of the 600 variable stars in the system has also been carried out (AJ 84,601). Here, a tidal radius of 47~6 is derived. A number of the variables are extra-tidal. Conclusions of their distribution are drawn. The Fornax dwarf galaxy has a wide giant branch (ApJ 232,84); the dispersion suggests the existence of a range of abundances among its stars. Also its globular clusters show a spread in metallicity with a least 3 clusters having lower metallicity than the field stars (AJ 86,357) and the most metal poor having lower metallicity than M15 (ApJ 247,849). The luminous stars in the two irregular dwarf galaxies "IGC 6822 and I: 1613 have been studied (ApJ 238, 65) as 1{ell as the history of their star formation

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(ApJ 241,125). Evidence for sporadic bursts of enhanced star formation is found. Kinman reports that 3 very compact HII regions have been found in NGC 6822 (PASP 91,749). The HI content of IC 1613 may be found in (AA Suppl 41.189).

A preliminary luminosity function for the recently found dwarf irregular galaxy in Sculptor (SDIG) has been presented (ESO Prepr. No. 155). It appears similar to those of IC 1613 and NGC 6822. In several of the dwarf spheroidal galaxies carbon stars have been identifie~ They were suggested to exist in the Fornax system in (PASP 91,761); later on a number were found there and in the Sculptor system (Messenger 19,7; ApJ 240,804). They have also been found in the Draco dwarf galaxy (Steward Obs. Prepr. 341). In the recently detected Carina dwarf galaxies 2 carbon stars have been found (MN 196,IP), but Cannon reports that now 8 are known; they appear similar to those in Fornax (talk at RAS, England, in March 1981). Of great interest is the detection of Wolf-Rayet stars In the dwarf galaxy Tololo 3 (AA 101,L5). The new Local Group dwarf galaxy LGS 3, probably a satellite to M 33, was observed in HI (ApJ 232,L11). CCD camera observations led to a value of MV =-7.1 mag for LGS 3, provided it has an old population, only. If it is at the distance of M33, its MV= -9.7, and it must contain a young population. An investigation of the stellar content of dwarf spheroidal galaxies, based on the construction of models for extremely metal-poor horizontal branch stars, is found in (ApJ 241,111). Further theoretical studies of dwarf galaxies are presented in (ApJ 242, 517); here a stochastic self- propagating star formation model is applied. Thuan reports on extensive studies of dwarf galaxies: 115 blue compact dwarf galaxies (BCDG) have been observed in HI. These data are combined with all available optical data for statistical studies (ApJ 247,823). In addition excellent spectra of 50 BCDG have been obtained as well as IUE observations of 7 BCDG. All UV spectra show strong NV, CIV anq NIV stellar absorption features with P Cyg profiles on the latter lines in some cases, indicative of stellar winds in these galaxies. Thuan is also continuing his HI study of the remaining Nilson (UGCG) low-surface brightness (LSB) dwarf galaxies, and he has begun a HI survey of all 1163 magellanic-type galaxies in the UGCG. These galaxies are intermediate in star-formation activity between the LSB galaxies and the BCDG. X-ray Einstein IPC observations have been obtained for two BCDG objects. X-ray emission is expected due to the large number of supernova remnants in these galaxies. ~inman reports that spectroscopic observations have been obtained of 10 emission-line dwarf galaxies (ApJ 243,127) and the abundances of He and 0 determined. The underlying continua in these galaxies come predominantly from mixtures of O-type stars and moderately hot giants and supergiants. The ratio of HI mass to total C!ass is found to increase monotonicallY with decreasing total mass.

A morphological study of 15 blue dwarf galaxies showed 3, possibly 5, to be dwarf ellipticals. The others had bright knots and other morphological perculiarities as dominating features (AA Suppl 37, 541).

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2. STRUCTURE AND EVOLUTION OF GALAXIES (P.C. van der Kruit) 1. Introduction

In the period covered by this report two major meetings were devoted to the subject of the structure and evolution of galaxies: "Photometry, Kinematics and Dynamics of Galaxies" (Austin, Texas) in 1979 and the NATO Advanced Study Institute on "The Structure and Evolution of Normal Galaxies" (Cambridge, ~!lgland) ire 1980. The review papers in the published proceedings of these meecings ::crovi::e a goo:: summary of the recent progress in the field. Other reviews of interest a::cpearei in IAU Symposia 84 and 94. Nuclei and active galaxies are not included in the report. II. Masses and mass-to-light ratios Mass determinations of spiral galaxies using the rotation curves In tie disks have been reported by Bosma (Ph.D. Thesis, Univ. of Groningen) and he also compiled rotation curves obtained using the HI-line at 21 cm. Generally flat rotation curves out to distances beyond the Holmberg radius are found. A similar result has been reported by Rubin and co-workers (ApJ 238, 471) from optical spectra who discuss also the comparison of the curves among Sc's as a function of luminosity and size. Much work has been devoted to the measurement of velocity dispersion in elliptical galaxies (AJ 85, 801; AA 91, 122; AJ 246, 666) with the general result that the luminosity L scales as L ~ 0 4 , with 0 the central velocity dispersion. The resulting integrated mass-to-light ratio is usually in the range 10-20 in reasonable agreement with results from double galaxies (Astroph. 15, 25; ApJ 232, 20; MN 195, 1037) where the last reference (White) reanalyses the Turner data and brings it into better agreement with other studies. Terlevitz et al. (MN 196, 381) have shown that there is good agreement in the velocity dispersion obtained by various groups of observers, but that it correlates with line strength (metallicity) in the sence that at a fixed absolute magnitude low dispersions occur in galaxies with low line strengths. The axis ratio may also playa role. The bulges of spiral galaxies too appear to follow a L 00 0 4 correlation but with a lower proportionality constant (ApJ 234, 68). Mass-to-light ratios have been reviewed by Faber and Gallagher (Ann. Rev. 17, 135). Bosma and van der Kruit (AA 79, 281) show that M/L increases dramatically with radius in spiral galaxies and van der Kruit (AA 99, 298) found from the thickness of the HI-layer in NGC 891 that this dark matter must be distributed outside the disk. Tinsley (MN 194, 63) finds that the integrated M/L of spirals is larger in blue galaxies, while Krumm and Salpeter (ApJ 84, 1138) show that it appears to be independent of type. Searches for extensive halos around spirals in the optical and infrared (AJ 85, 131; AJ 86, 178; ApJ 244, 476) remain unsuccessful. Using X-ray observations Fabricant et al. (ApJ 241, 552) estimate the mass of M87 to be 4 x 1013 Me • With present uncertainties of the dynamics of elliptical galaxies (see below) there is as yet no convincing evidence of radial increases of M/L in elliptical galaxies. This also accounts for the lack of agreement on whether the observations demand that there is a large condensed central mass in M87 (see also below). III. Structure Burstein (ApJ 234, 435/829) has studied So-galaxies and performed bulge-disk separations. He suggests that these system have a third component ("thick disks") that spiral galaxies lack. Boroson (ApJSuppl 46, 177) studies bulges and disks ln a large sample of spiral galaxies., Van der Kruit and Searle (AA 95, 105) study

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edge-on systems and propose a model for the three-dimensional distribution of light in spiral disks. This may also be the distribution of mass in these disks (AA 99, 298). The deformed outer spheroids in spiral galaxies may be similar to "thick disks" in So-galaxies. The bulge of NGC 891 becomes bluer with increasing radius (AA 95, 116) presumably as a result of decreasing metal abundance. Wirth (AJ 86, 981) finds the same result for late type spirals, but finds no such trend among ellipticals. In M87 both the smooth light and that of the globular clusters becomes bluer with distance from the centre (Strom et al. ApJ 245, 416), but at each radius the clusters are bluer (presumably more metal poor). This is also true in three other Virgo ellipticals (ApJ 245, 19), while the density of clusters falls off less steeply than that of the light. It remains unclear whether non-giant ellipticals have in general abundance gradients. Schweizer terminations of Cappacioli (ApJ propose it as a

(ApJ 233, 23; AJ 86, 662) has studied the effect of seeing on decore radii and finds the effects to be sincere. De Vaucouleurs and Suppl 40, 699) published photometry of the elliptical NGC 3379 and standard for surface photometry.

Talbot, Jensen and co-workers have performed a detailed study in various colours of the spiral M83 (ApJ 229, 91; 243, 716). Their work shows how the star formation has proceeded in the disk and how it relates to the spiral structure. No compelling evidence for the presence of density waves in M83 has emerged. Radio continuum studies of spirals and the conclusions concerning the orlgln of cosmic rays are reviewed in IAU Symp. 94. Papers have been published on the presence of thermal radio emission (AA 94, 29) and on the magnetic field in M31 (Nature 283, 272). Hummel reported on a major radio continuum survey of galaxies (AA Suppl 41, 151; AA 89, L1; 93, 93). HI-distributions in spiral disks have been published for many systems (e.g. Bosma thesis), notably in detail for M33 and IC343 by Newton (MN 190, 689; 191, 169; 615) and for M31 by Urwin (MN 190, 55; 192, 243). Sancisi et al. (AA 78, 217) studied the barred spiral NGC 5383. The thickness of the HI-layer of NGC 891 has been measured by Sancisi and Allen (AA 74, 73) and has been discussed also by van der Kruit (AA 99, 298). HI-maps of the So-galaxy NGC 1023 are published by Allsop (/'!N 187, 537) and of the elliptical galaxy NGC 4278 by Raimond et al.(ApJ 246,708). IV. Dynamics and Evolution Much effort has been devoted to the dynamics of elliptical galaxies, as also evident from the proceedings of the two conferences in Austin and Cambridge. Some references to various aspects are: numerical models (ApJ 232, 236; 235, 793; 243, 111; 121); rotation U.rn 190,421); anisotropic velocity dispersions (ApJ 227,56; :·::l 189, 791; ApJ Suppl 41, 209; ApJ 244, 458) and reviews in Austin and Cambridge. E~liptical galaxies may be supported by anisotropic velocity distributions. This makes it difficult to rule out MIL gradients, because usually plausible anisotropics can be invoked to explain the observations. The observations of a possible dark, centrally condensed, massive object near the centre of M87 can be explained as well by invoking anisotropy in the velocity distribution (ApJ 237, L27). Bulges of spiral galaxies are rotationally supported (Illingworth in Austin and Cambridge and see also ApJ 235, 30). Although still defended by van den Bergh (AJ Can. 73, 198), many authors now contend that sweeping cannot be the major cause for the occurrence of So-galaxies: Burstein (ApJ 234, 435) and Boroson (ApJ Suppl 46, 177) on the basis of disk-tobulge ratios; Dressler (ApJ 236, 351) on the basis of occurrence of types as a function of environment, Larson et al. (ApJ 237, 692) on considerations of gas

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consumption by star formation in spiral galaxies. Density waves as the cause of spiral structure is supported by the existence of streaming motions in M81 (AA 58, 149; 159), but other interpretations are not ruled out. ~o streaming is found in M33 (MN 190, 689) and IC342 (MN 191, 615). Kormendy and Norman (ApJ 233, 539) find that there is observational evidence that spiral structure and density waves occur only in galaxies with oval distortions, bars or nearby companions. Stochastic star formation as the cause of spiral structure (or its ab3en~e in dwarfs) has been explored by Seiden, Gerola and co-workers (ApJ 232, 702; 233, 56; 242, 517). Streaming motions in barred spirals have been studiei by Sancisi et al. (AA 78, 217) and Rubin (ApJ 238, 80B). Gas dynamical models have been publi.shec. Roberts et al. (ApJ 233,67) and Sa'1ders and Tubbs (ApJ 235, B03). ':'~!e exit and persistence of gaseous warps in the outer parts of spiral disks has bee" 1'1vestigated by Tubbs and Sanders (ApJ 230, 736), Petrou (HN 191, 767) aeli 3ertin and l':ark (AA BB, 2B9). Baldwin et al. (MN 193, 313) studiec. the lobs idee. structure of gas disks. The chemical evoLltion in galaxies has been reviewed by Pagel (Stars al'ri Star Systems, p.17) and Tinsley (Fun. Cosmo Phys. 5, 2B7). Searle (Liege Conf.1978, p 437) discussed abundances in globular cluster systems. Work on galaxies in the Local Group and d1mrf galaxies has been published by Lequeux and cO-Horkers (AA 71 1; BO, 155).

v.

Interacting and merging galaxies

Many investigators have emphasized the importance of merging betHeen galaxies in clusters, for the cluster evolution. Model calculations (AA 76, 75) ShOH that merging is most frequent in the early collapse phase of the evolution of the cluster; due to the increased velocity dispersion in the later stage the merging proceeds slower. The proportion of merged galaxies seems to be fairly insensitive to variations in the expansion rate of the universe (AA 95, 349). The merging between gas-free axi-symmetrical systems should produce remnants with luminosity profiles similar to those of ellipticals and they should rotate slowly (ApJ 236, 43; MN 189,27;B31).However, compared with observations of normal ellipticals the model galaxies appear to rotate too fast. The population mixing due to the merging appears to be weak; it may be masked by other effects such as induced star formation (ApJ 239, L9). It may thus be difficult to distinguish between normal ellipticals and mergers. Some statistical properties of ellipticals seem to invalidate the assertion that the bulk of these galaxies were formed by recent mergers (Comm. Astroph. 8. 177). However, if the merging occurred during the collapse phase these arguments may be weakened. The importance of subclustering has been emphasized (ApJ 236, 43; MN 191 1p); the more compact a group the more frequent the merging. Observations appear to have confirmed this (ApJ 248, 439). Of the isolated compact groups of interacting galaxies observed today, about 5-15 percent may have originated from tight groups (AZh 56, 936). A correlation appears to exist between the dynamical timescale of a cluster and its Bautz-Morgan type, which could be understood as an effect of merging. A number of individual galaxies have been suggested to be the result of a merging or to be in interaction with nearby objects. A detailed morphology of NGC 1316 (Fornax A) shows irregularities that indicate that dynamical equilibrium is not yet achieved (ApJ 237, 303; 246, 722). It has a strongly inclined, rapidly rotating nuclear disk, which may have formed about

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10 9 years ago when a few gas-rich galaxies fell in. A similar case of a merging between a gas-rich and a gas-poor galaxy is IC 1182 (ApJ 247, 42). Possible cases of merging between two gas-rich galaxies have been reported: NGC 3310 could be a merging between a ~piral and an irregular galaxy (AA 96,271); NGC 6240 appears to be the result of the encounter between two galaxies of similar mass (MN 189, 79); and NGC 520, previously assumed to be a single exploding galaxy, consists most likely of two galaxies in close tidal interaction (AA 74, 110; ApJ 235, 37). Similar cases are discussed in (AA 97, 302; AA Suppl 35, 55). NGC 6052 (AA 78, L5) may be the result of the collision between two late spirals with a high rate of star formation induced in the central regions and the formation of supergiant HII regions in the outer parts. A quadruple system of galaxies, ESO 255IG07, is reported by Bergvall et al. to be in the stage of merging (AA 95, 266). the cal 71, 84,

A number of systems in different 21-cm line and analyzed in detail, data: NGC 672/IC 1727 (AA 84, 85); 131); NGC 4214(4190 (MN 188, 765); 1830); and Arp 205 (MN 187, 509).

stages of interaction have been observed in in some cases in the ·combination with optiNGC 1512/10 (AA 76, 230); NGC 4038/39 (AA NGC 4490/85 (AA 82, 207); NGC 4725/47 (AJ

A catalogue of interacting and merging galaxies south of declo -37~ 5, b < - 30 0 , has been prepared by Bergvall (preprint). It contains 371 systems of interacting galaxies and 47 distorted single systems. 3. GROUPS AND CLUSTERS OF GALAXIES (P. W. Hodge) More than 250 significant papers on groups and clusters of galaxies can be found in the literature published since 1 January 1979. It is obviously not possible to report on every paper, and so the following cites only a few representative references to work in each of the categories. Several good reviews of the subject were written, e.g., by Bahcall (Highlights of Astr., 5, 699), Giacconi (X-ray and Gamma-ray Astr. in 80's, 33), Quintana (1st Latin-Am Reg. Astr. Mtg., 75); Huchtmeier and Materne (The Messenger, No.25, 8), and Rood (Repts. on Progr. in Phys., in press). I. Morphology and Populations Hickson (ApJ, in press) and Baier and Tiersch (Astrofiz. 15, 33) published new catalogues of compact groups, and Wakamatsu and Malkan (PAS Japan, 33, 57) reported the optical discovery of a cluster behind the Galactic center. Rudnicki et al. (in press) reported that Zwicky's ED-type clusters are probably mostly misidentified single low-surface brightness objects. Cluster types were the subject of certain revisions by Struble and Rood (AJ, in press), while Rood (ApJ 233, 21) studied the shapes of galaxy groups, finding that the average ellipticity is ~0.25. ~Iany studies of the Hubble types, brightnesses, and colors of galaxies in clusters were reported, including a massive survey by Dressler (ApJ Suppl 42, 565), giving data on 6000 galaxies in 55 rich clusters. Butcher et al.("Objs. of High Redshift", p. 49) examined colors of galaxies in several very remote clusters, concluding that they contain some galaxies with active star-formation and Gisler (AJ 85, 623) concluded that new statistics of morphological types in clusters argue that stripping of spirals does not explain SO galaxies in clusters. Hoessel et al. (ApJ 241,486; 493) carried out surface photometry of brightest cluster galaxies in 116 Abell clusters, finding a correlation between absolute magnitudes and the structure of the galaxies with the properties of the host clusters. Paturel (AA 71, 106) analyzed the population of the Virgo cluster with a

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new taxonomic approach and Borngen (AN 301,305) searched the Virgo cluster for faint blue members. Richter (AN 302, 31) carried out a search of clusters for red compact members. Thuan et al. (ApJ 248, 439) examined giant E's in poor clusters and Bahcall (ApJ 238, L117) classified types for galaxies in 23 poor clusters, finding a continuum of populations, smoothly blending into rich cluster morphologies. Worth and Gallagher (ApJ 242, 469), Carter (MN 190, 307), and Weekes (AJ 86, 1415) photometrically studied the galaxy content in a few individual clusters. Luminosity functions, studied for a wide range of types of clusters by Bahcall (ApJ 232,689), were derived for several additional rich clusters (e.g., by Bucknell et al. MN 188, 579 and Thompson and Gregory, ApJ 242, 1). Takase (PAS Japan, 32, 605) showed that, compared to the field, cluster popUlations are deficient in UV-bright galaxies. II. Structure and Dynamics \Yi th the increased availability of fast spectrographs, a great deal of ne'" material is available on velocities of members of clusters of galaxies. Analyses of the velocity dispersions and observed structure of clusters has provoked a number of increasingly realistic theoretical models of their dyna~ics. Comparisons of structure and velocity dispersions with models, including N-body si~ulations, were made by Gott et al. (ApJ 234, 13), Smith et al. (ApJ 234, L97), Dautcourt (AN 301, 155), Struble (AJ 84,27,40,50, Ap. Sp. Sci. 64, 301) and others. Rose (ApJ 231, 10) showed that compact groups are often transient phenomena. The Coma cluster was compared to models by Quintana (AJ 84, 15) and by Sarazin (ApJ 236, 15) both concluding that some mass segregation has probably occurred. A new statistical test of clustering (Bonometto and Lucchin, ApJ 228, L5) and a neli non-linear, thermodynamical approach (Saslaw_ ApJ 235, 299) to cluster dynamics were developed. Cannibalism by central massive galaxies was further investigated by McClynn and Ostriker (ApJ 241,915) and several astronomers pointed out the dynamical importance in many clusters of binary massive central objects (Ozernoy and Reinhardt, Ap. Sp. Sci. 60, 267; Valtonen and Byrd, ApJ 230, 655, Rood and Leir, ApJ 231, L3; Wesson, AA 90, 1; and Quintana and Lawrie (preprint). A discussion of the importance of primordial conditions and of galaxy formation was written by Fall (Phil. Trans. R. Soc. London, A 296, 339). Rudnicki et al. reported (Acta Cosmo Z. 9, 53) the detection of some sub-clustering tendencies in clusters. The missing mass continued to occupy the attention of several astronomers, with some of the papers mentioned above concluding that massive binary galaxies could alleviate the problem for some clusters; historical mass-loss (Ikeuchi, PAS Japan 31,169) masssegregation (Saito and Tosa, PAS Japan, 31,625), and modified gravitational theories were also investigated and were found to be able to eliminate or greatly reduce the mass discrepancy. Detailed structural studies of individual clusters were reported by MacGillivray and Dodd (0041-2946 cl, MN 186, 143); Baier (51 clusters, AN 300,85,133,243; 301, n, 165); Ziener (A1831, AN 300,203); Quintana and Bavlen (CA 0340-538, AA 19, 10); Chincarini et a1. (N5416 cluster, AJ 84, 1500); Reakes (MN 187, 525 and Bosma et al. (AA 89, 345; both on the NGC 2805 group); Capelato et al. (Coma, ApJ 241, 521); Kirshner and Malumuth (Sh. 1 group; ApJ 236, 366); Danese et 8.1. (43 clusters, AA 82, 322); Tully (N1023 group, ApJ 237,390); Jones and Jones (Fornax cluster, MN 191, 685), Thompson et al. (N5416 cluster, PASP 90, 644), and Dressler (A2829, ApJ 243, 26).

III. X-ray Clusters Since the discovery of X-ray emission from clusters of galaxies, a large amount of liork has gone into establishing the mechanism involved and the evolution of the characteristics of the X-ray-emitting gas. Only a brief summary follows, as this topic is also covered in the report of Commission 48. The radiation characteristics seem nOli to establish the mechanism as thermal bremstrahlung fro~ a hot intracluster medium (e.g., Strimpel and Binney, HN 188, 883; Bahcall, ApJ 232, L83, and many others), with only a few cases of cooling reported for the cores of r~ct

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clusters (e.g. Mushotzky et al. ApJ 244, L47). A wide variety in the structure of X-ray sources seems to be related to the present and past structure of the clusters and galaxy formation therein (Jones et al., ApJ 234, L21; Ulmer et al., ApJ 235, 351; Perrenod and Henry, ApJ 247, L1, Schmidt, AN 301,297; and many others). Many cD-dominated clusters were found to have their X-rays concentrated in the central galaxy, and sometimes its halo (Schwarz et al., ApJ, 231, L105, Kriss et al., ApJ 235, L61, Johnson et al., ApJ 236, 73e), a situation that was studied theoretically by Takahara and Takahara (Prog. Theor. Phys. 62, 1253). Tenuous, diffuse haloes were searched for but only found in the Perseus and Virgo clusters (Nielsen et al., MN 189, 183, and Ulmer et al., ApJ 236,58). A promising tool for investigating cosmologically important data, especially the velocity of clusters with respect to the cosmic background radiation, was proposed by Sunyaev and Zeldovich (MN 190, 413), and Melchiorri et al. (AA 74, L20), and investigated by White and Silk (ApJ 241, 864), Lake and Partridge (ApJ 237, 378) and Boynton et al. (preprint). IV. HI and Gas-Stripping The old idea of tidal and/or collisional stripping of gas from cluster galaxies by close encounters was examined by comparison of 21-cm with optical and infrared data for cluster members. Livio et al. (ApJ 240, L83) examined the process of stripping of gas from galaxies by passing through a hot intracluster gas and several papers reported evidence that at least some cluster galaxies are anomalously gas-poor (Sullivan et al. AJ 86, 919, Schommer et al, AJ 86, 943, Giovanelli et al.ApJ 247, 383), although many clusters (particularly those less dense than Coma) show no good evidence for this process (Bothun, Ph.D. thesis, U. Washington). For several small groups, high-resolution HI studies demonstrated the probable influence of tidal interactions on the gas distribution in and around cluster members (Allsopp, MN 188,371; Davies et al., MN 191, 253; Hart et al., MN 191, 269). V. Radio Surveys With increased use of interferometric arrays, radio continuum surveys of clusters became possible with increased resolving power, allowing beautifully detailed maps to be made of interesting radio structures in clusters. For example, an extensive series of papers resulted from a Westerbork Survey of clusters of galaxies (e.g. Gavazzi and Perola, AA 84, 288, which is paper XII). Other radio surveys were published by Waldthause et al. (AA Suppl 36, 237), Gisler and Miley (AA 76, 109), Simon (MN 188, 637), Andernach et al. (AA Suppl 41,339; 43, 155), Harris et al. (AA 90, 283; AA Suppl 42, 319), Johnson (ApJ Suppl in press) and Hanisch (AJ 85, 1565). The subject of the presence of diffuse radio emission and radio haloes was investigated, but though many clusters were searched, the only nearby clusters with confirmed detections were the Coma and Virgo clusters; e.g., see Hanisch et al., (AJ 84,946), Jaffe and Rudnick (ApJ 233,453), Birkinshaw (MN 190, 793), and Hanisch and Erickson (AJ 85, 183). VI. Superclustering Although most workers in the field seem to accept the existence of superclustering, some papers were presented that claim to make their existence either incorrect or unnecessary (MacGillivray et al., Ap. Space Sci. 67,237; Fesenko, Astrof. 15, 599). The more common viewpoint pictures the arrangement of clusters either in somewhat hierarchical second-ordered clusterings or in a net-like framework, separated by immense voids. The local supercluster (de Vaucouleurs BAS India, 9, 1), that made up largely by Coma and A1367 (Williams and Kerr, AJ 86, 953; Chincarini and Rood, ApJ 230, 648), and the Hercules supercluster (Tarenghi et al., ApJ 234,793; 235, 724) were studied in considerable detail. More general

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surveys of nearby superclustering were made by Einasto et al. (MN 193, 353, and Nature, 283, 47) and by Rood (ApJ 233, 431), while dynamical models of superclustering were proposed by Gerbal and Salvador-Sole (AA 87, 165) and by Miller ( private communication).

4. COMPACT GALAXIES, QUASARS AND RELATED OBJECTS (B.E. Westerlund) Compact galaxies Compact galaxies have been identified on Tautenburg Schmidt telescope plates, photometry has been carried out and the material has been statistically analyzed (AN 300, 281; 301, 301; 302, 29). Identifications are also found in (Ast~ofis. 15, 393; Astrofis 16, 25). A summary has been presented by N. Richter {Vistas in astr. 23, 143). A spectroscopic survey of 145 blue compact Zwicky galaxies gave 39 emission-line galaxies, 6 Seyferts. The remaining objects were galaxies with no emisson or galactic stars (AA Suppl 36, 259). Kinman has obtained spectroscopic and photometric data for 23 faint compact uv-excess gaJaxy candidates. (PASP Aug 81).18 were found to be emission-line galaxies with redshifts between 1 670 and 39 450 km s-1. The chemical composition and evolution of irregular and blue compact galaxies has been examined (AA 80, 155). The two ty~es differ only in the present rate of star formation. The blue compact galaxy IZw 18 may be a galaxy in the process of formation by merging of primordial clouds (AA 91,269). The COSMOS measurements of UK Schmidt telescope plates for faint blue objects gave two distinct populations (ApJ 237, 371): diffuse images with a colour distribution consistent with high-redshift galaxies, and compact blue objects which appeared to be quasars. The N galaxy Markarian Mk 421 is a composite system with a mlnl- BL Lac object and a considerably fainter giant elliptical. Its variations on X-ray and optical wavelengths have been discussed (ApJ 241, 74). Many Markarian galaxies may fall into the category compact galaxies; a particular class may be the clumpy irregular galaxies. Heidmann reports on spectroscopic and/or 21 cm investigations of some objects of this type (AA 73,216; AA Suppl 37, 559; Nature 282, 272; MN, in press and ApJ, in press). The clumps are about 100 times more massive than the giant HII region 30 Dor in the Large Magellanic Cloud; each galaxy has about 5 to 10 bright clumps. It is likely that these galaxies are sites for star formation on an exceptional scale. (See also e.g. Publ. Astr. Soc. Japan, 31, 329; 31. 635). Active galactic nuclei Morphological and spectroscopic criteria place N galaxies, Seyfert galaxies, QSOs and BL Lac objects in this class. Much theoretical work as well as many spectrophotometric investigations deal with active nuclei more generally. A review of the theories of the nuclei of active galaxies has been presented (Proc. R. Soc. London, Ser. A 366, 449). Extreme nonthermal radiation from this kind of nuclei has been discussied (ApJ 238, L63). The possibility that some active nuclei contain two massive black holes in orbit about each other has been considered (Nature 287, 307). The importance of a magnetic field in the accretion disk for the nonthermal activities has been studied by Takahara (Prog. Theor. Phys. 62, 629), who also investigated the Comptonized spectrum (Prog. Theor. Phys. 63, 1551; 65, 883). Takahara et al. (ApJ, in press) show that Comptonization of soft photons in

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In a hot magnetized plasma can account for the observed features of X-ray emission of active galactic nuclei. Compton-heated winds from accretion disks in QSOs have been studied by Shields et al. (in prep.). Emission-line spectra of active galactic nuclei have been reviewed by Osterbrock (Ann N.Y.Acad. Sci. 336, 22). He has discussed the ionized gas and the dust in them (AJ 84, 901), and presents with Shuder results from a spectrophotometric investigation (ApJ, in press). Infrared spectra of the nuclei of 3 active galaxies are described (MN 196, 101P) and dust-emission mechanisms considered. Seyfert galaxies X-ray observations of Seyfert galaxies with the Einstein Observatory added 17 Seyfert 1 and 4 Seyfert 2 galaxies to the 30 and 5, respectively, previously known to emit X-rays (ApJ 242, 492). The Seyfert 2 galaxies appear to be lowluminosity exemples of the same processes as occur in Seyfert l~s. The X-ray Seyfert 1 galaxy NGC 6814 has been found to show X-ray variability on timescales of less than 3 hours; this is in sharp contrast to a sample of over 30 active galactic nuclei (NASA Tech. Mem 82143). X-ray observations are also described in (ApJ 235, 355; 235, 377; 237, 414; 239, L5; MN 189, 37P; 192, lP). A massive X-ray halo may exist around the Seyfert 1 galaxy Mk 541 (AA 72, L6). A variable iron emission feature has been found in the X-ray spe.ctrum of NGC 5548 (MN 193, 15P). IUE observations of Seyfert galaxies may be found in the proceedings of the symposia "The First Year of the IUE"; Second European IUE Conference". A.Elvius reports that in May 1981 more spectra of NGC 7469 were obtained with the IUE. The object was slightly fainter and the spectrum not as hard as in 1978. A study of the velocity field of this object has been presented (AA 89, Lll). CIV 1550 A line profiles have been measured for 4 Seyfert 1 galaxies (ApJ 247, 449). Possible line broadening mechanisms are considered. The CIV lines are at lower redshift than the Balmer lines. Osterbrock reports on the spectrum of the high-ionization Seyfert 1 galaxy III Zw77 (ApJ 246, 696; see also AA 76, 50), and on a new Seyfert 1 galaxy (PASP 92, 117). He has analyzed the spectra of 5 galaxies with line and continuum spectral properties intermediate between those of Seyfert 1 and 2: they are called Seyfert 1.8 and 1.9 galaxies (ApJ Oct 15, -81).M.P. Veron has shown that most of the narrow-emission line nuclei are either normal HII regions ionized by hot stars or Seyfert 2 galaxies (AA 100, 12); the separation can be done unambiguously on the basis of relative line intensities. In some cases the two types of emission nebulosities co-exist in the same nuclei (AA 97, 71). Several authors have analyzed emission-line profiles, studied broadening mechanisms and/or the structure of the emission-line regions in Seyfert galaxies by spectrophotometric means (See e.g. ApJ 230,360; 230, 681; 233, 809; 238, 45; 238, 502; 238, Ll; 241, 903; 247, 403; AA 81, 172; 87, 245; AJ 84, 302; Astrofiz 16, 39; MN 191, 665 ; 195, 787; Proc. Southw. Reg.Conf. 5, 87). Broad-band infrared observations have been presented for 16 Seyfert galaxies of which 7 are X-ray sources (ApJ 234, 471). The Seyfert 2~s are dominated by a stellar continuum, the Seyfert l~s - and all the X-ray objects except one - have power-law spectra. Spectrophotometry from 2.1 to 4.0 ~m of 3 Seyfert galaxies is described in (ApJ 245, 818). The 3.3 ~m emission feature has been detected in the nuclei of IC 4329A, an extreme Seyfert 1 galaxy, and NGC 5506, a narrow-line X-ray galaxy, possibly with a Seyfert 1 nucleus (AA 100, L6). Multiaperture photometry of NGC 1068 has demonstrated that significant 20 ~m emission originates at positions more than 3" from the nucleus (ApJ 241, L69). This supports arguments that most of the infrared flux is thermal emission from dust. The detection of millimeter-wave CO emission from two Seyfert galaxies has been reported (ApJ 247, 443). The width of the lines was smaller than those of the corresponding HI profiles. Radio maps of 10 Seyfert and Seyfert-like galaxies have been made with the VLA (ApJ 240, 429;

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247, 419). A high sensitivity survey with the Westerbork telescope at 1415 MHz has been presented (AA Suppl 45, 99); it contains 36 Seyferts and 10 possibly Seyfertrelated. Detection of H83a and H99a radio recombination lines in Mk 668 has been reported (ApJ 238, 818). The variability of Seyfert galaxies has been investigated (see e.g. PASP 90,661; 91, 624; AA Suppl 35, 387; MN 186, 297; Nature 284, 410). Morphological studies of Seyfert galaxies have been carried out (ApJ 237, 404). An extraordinary emission-line nebulosity has been found to be associated with Mk 335 (ApJ 247,32). An enormous HI envelope has been found around the Seyfert galaxy Mk 348 (ApJ 238, 17) • Among the most studied Seyfert galaxies is NGC 4151. Gamma-rays at energies above 100 MeV have been observed from it (Pis~ma AZh 5, 317) as well as a lowenergy gamma-ray spectrum (Non-solar gamma-rays, p. 67; Nature 282,484) and models have been proposed (AA 87, 192; 89, 370; ApJ 240, 636). X-ray spectral data have been obtained (ApJ 241,113; 247, 458), and frequent flaring of its X-ray source, on a time scale of days, has been observed (MN 192, 83). During the first 4 years of the IUE near 200 spectra have been taken of NGC 4151. Results from the first year are in press (MN 196), describing the continuum, 15 identified absorption features and many emission lines. A second paper, describing the variations of the continuum has been submitted to MN. Comparisons with Xray and optical observations are presented. The large international group collaborating in this project reports that several papers will follow, possibly including an atlas of representative IUE spectra of NGC 4151. The emission feature at 3.3 wm has also been detected in NGC 4151 (ApJ 241, 1141), and infrared variability has been confirmed (ApJ 245, 818). Optical polarization studies of the emission lines and the continuum of NGC 4151 have been undertaken (ApJ 229, 909; 240, 759). The nuclear continuum of NGC 4151 has been investigated (Publ Astr Soc Japan 32, 185). It was found to have an essentially flat spectrum. Quasars 111 QSOs were examined with the Einstein Observatory (Nature 288, 323) and 35 of them were detected as X-ray sources. More recently observations of 107 QSOs with the Einstein Observatory have been reported (ApJ 245, 357) with the detection of 79. In both cases a correlation between the 0.5-4.5 keV properties and the optical and radio continuum properties was found. Optical spectra of 6 X-ray selected QSOs have been described (ApJ 239,143), they are radio quiet, have relatively faint B mag (~ 18)and low redshifts. The IUE satellite has been used for stUdying selected QSOs (see e.g. ApJ 239, 483; 245, 386; Nature 277, 457). The ratios 1a/Ha and La/HB have been discussed for a number of objects (ApJ 227,Ll; 228,8; MN 187,871), the intrinsic values are most likely appreciably larger than the observed ones. Corrections for reddening are necessary (ApJ 230,348). In the spectrum of 3c48 (ApJ 230,340) the forbidden lines are blue-shifted relative to the permitted lines; the Balmer lines can be decomposed into a narrow and a broad component. The MgII 2798 emission in QSOs and related objects is frequently composed of broad and narrow components (ApJ 232, 659). Gaskell (ApJ, submitted) has found that the high-ionization (emission) broad lines are blueshifted with respect to the low-ionization broad lines in almost all quasars. The emission line profiles of CIV 1550 show similarities between species of differing ionization potentials; the lines may be formed in a number of clouds of different velocities (ApJ 240,1). The CIV line has been suggested to be useful as a standard

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cosmic candle (Nature 273, 431; MN 193, 537; BAAS 12, 537). The idea about (radiatively) accelerated emission-line clouds in QSOs has been analyzed (ApJ 233, 479; 241, L157) as well as the effects of dust within the broad-line emission regions (ApJ 235, L125). Absorption of X-rays within the broad-line emitting clouds has been investigated (ApJ 245, 406). From a large sample of QSOs it has been found that the spectra are well approximated by power laws with spectral indices ranging from +0.3 to -2.5 (ApJ 235, 361). A broad wave is seen in residuals; it appears as a deficiency near 2 000 ; and 4 000 ; and an excess near 3 000 A. It can be explained completely by Balmer line and continuum emission together with a large amount of Fell emission (Gaskell, thesis, Univ. of Calif). The same conclusions have been drawn by Shields and Oke (in prep.) who propose that the Balmer continuum can be produced in gas heated at large optical depths by gamma rays of energy ~ 1 MeV. The importance of the blended Fell resonance lines has also been pointed out in (ApJ 237, 119; 242,

L1).

High-resolution spectroscopic observations of quasars have led to the detection of multiple absorption-line systems in many objects (see e.g. ApJ 228,1;230, 49; 230,330; 234, 33; MN 188, 711; 189, 611). As a rule most lines longward of the La emission line have been successfully identified but only few lines shortward of it (ApJ 229, 891; MN 196, 715). The metal-line systems may arise in galactic halos whereas the La clouds must be an intergalactic population (ApJ Suppl 42, 41; see also ApJ 241, 889). An intrinsic model for the formation of narrow absorption-line systems in gas from the QSO has been presented (MN 191, 785; 195, 397). They may also form in thin shells of negligible densities (MN 186,1). The absorbing clouds may be only a few parsecs from the QSO (ApJ 227, L113) when they are optically thick; or the minimum distance may be as large as 750 kpc (ApJ 230, 330), and they are not ejected by the QSO. Call absorption lines have been detected in some objects and located to intervening galaxies (ApJ 242, L145; Anglo-Austr. Obs.Prepr. 128); this supports the idea that the narrow-lines heavy-element absorption systems in QSO spectra arise In extended galactic halos (see also ApJ 244, 768). 21-cm absorption lines have been detected in QSOs at redshifts corresponding to those of optical absorption (ApJ 230, L1; 232,49; AJ 84,699).Molecular hydrogen lines have been observed in the ~pectrum of OQ 172 (Ap Lett 20, 67) and in PHL 957 (Pis'ma AZh 5, 371), in the latter also absorption of CO is reported. Infrared observations have been used in combination with other data to determine bolometric luminosities for some QSOs (MN 192, 37P). Observations at 2.2 Wm at the positions of flat-spectrum radio sources led to the detection of a group of QSOs with much steeper infrared-to-optical spectra (a ~ -3) than previously known (ApJ 232, L151). Their energy distributions are consistent with a BL Lac nature (ApJ247,780). Radio structures of more than 150 QSOs have been examined with the NRAO interferometer (ApJ Suppl. 39, 291; AJ 84,707). The radio spectral properties of 74 QSOs have been studied (AA 73, 40). A sensitive search for radio recombination lines towards 24 galaxies and QSOs has been reported (AA 77, 316). A sample of 96 QSOs and other blue objects, chosen on the basis of optical variability, have been observed with the VLA (ApJ 242,486). Only 3 were detected; they are among the most variable in the sample. Other radio studies of optically selected QSOs indicate a detection rate of 35 to 50 percent at 5 GHz for the most luminous ones (MN 191, 871; Nature 283, 357), for the fainter ones it is about 10 percent. The radioto-optical luminosity ratios may be correlated with optical properties and/or distance (AA 88, L12; ApJ 238, 445; 242, 486; 246, 624). An exceedingly large amplitude radio outburst was recorded for the QSO 1921-29 (Nature 283,747) making

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it the strongest QSO in the sky at 31 GHz. Evidence has been presented for a radio outburst occurring 2.2 yr after a preceding optical outburst in the QSO 0420-01 (ApJ 227, L9). Numerous VLBI observations of QSOs have been carried out. Exemples are the maps of the quasars 3C 119; 286; 345; 454.3 and CTA 102 with a resolution of 0';005 at 1.67 GHz (ApJ 236, 714); of 3C 147 and 3C 380 (ApJ 235, 11); and of the nucleus of 3C 390.3 (ApJ 240, L7). Optical spectroscopy of a large number of radio sources has been carried out to confirm their QSO nature and/or to determine redshifts (see e.g. ApJ 229, 73; 232,400; 236, 419; MN 189, 667; 192,545; AN 300,37; 117; 287). QSOs detected in the Tololo surveys have been studied in detail (cf. ApJ 227, 18; 233, 757; _2.pJ Suppl 42, 333; 523; MN 189, 363; ApJ 238,488) and ~ie material has also been analyzed statistically (ApJ Suppl 42, 333; ApJ 239, 463; 247, 762). The optical search for faint radio-quiet QSOs has continued (see e.g.AA 78, 125; AA Suppl 39, 129; AN 301, 51; 301, 30); ApJ 231, 653). ~he nUlliber-magn~tude relation for optically selected QSOs has been discussed (AA 85, 80), a strong cosmological evolution is indicated (see also MN 195, 497; ApJ 245, 375; 246,365). The Hubble diagram and the luminosity function for radio-quiet QSOs are commented upon (AN 300, 197). Data on the X-ray emission from QSOs and on the X-ray background provide strong limitations on the number counts of QSOs (AA76, L1). Some evidence for a real association between QSOs and galaxies has been presented (Nature 282, 451), in particular with clusters of galaxies (ApJ 236, L45; ApJ 240, 25; Nature 290, 480), and possibly also with superclusters (AA 95, 7). No definite evidence for associations are found in some cases (AA 96, 393; ApJ 21+6,L1) and statistical analyses appear to indicate random distribution effects (ApJ 237, 326; AA 76, 254; 81, 316; see also ApJ 244, L53). Peculiar configurations of quasars may indicate physical associations (Nature 282, 271). Their alignment with galaxies may contribute to a definite solution to this problem (ApJ 229, 496; 229, 489; 233, L97; 236, 63; 240, 415). The possible effects of gravitational focussing should, however, not be overlooked (see below). The double quasar 0957+561A,B was presented at the IAU General Assembly in Montreal as a possible effect of a gravitational lens (see also Nature 279, 37 l,; 279, 381). Radio studies (Nature 280, 461) have revealed at least four components of which two coincide with the optical QSOs. The possibility of a gravitational lens is further discussed on the basis of spectroscopic observations with the multi-mirror telescope (ApJ 233, L43). Direct imaging led to the possible detection of an object between the two QSOs (Nature 282, 183). VLBI observations at 1666 MHz showed two apparently unresolved (~ 20 marcs) sources with the same separation as the optical objects. Intervening neutral hydrogen was looked for in the direction of the objects (Nature 283, 175) and limits derived. 1.2 - 2.2 ~m observations of the system supported the conclusion that the twin quasars are images of a single object (Nature 285,91). The intervening galaxy is shown to be highly luminous. Further infrared observations conflrmed that the lens galaxy is a giant elliptical (Nature 285, 385). VLA observations at 6 cm confirmed the major features previously reported (Science 208, 495). The existence of radio jets associated with both QSOs was demonstrated. Further VLA observations confirm earlier maps and show additional features (Nature 286, 865). UV observations of the obj~cts have been obtained (Nature 285,461). New spectrophotometric data (ApJ 238, 1) showed that the absorption line regions in each light path is very similar in redshift, in coloumn density of Fe+ and in

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velocity dispersion. A 408 MHz map provided spectral information on all components of the radio source (Nature 288, 69) and showed a weak component coinciding with the lens galaxy. Dyer and Roeder have shown that when a spherical galaxy acts as a lens there must always be an odd number of images of the source (ApJ 238, L67). Further VLBI observations have revealed radio fine structure in the two image components A and B (Nature 289, 758). Extremely deep CCD pictures of the region of the twin quasar show that they are behind a rich cluster of galaxies (ApJ 241, 507). The southern quasar image is seen through the brightest cluster galaxy. The cluster and the brightest cluster galaxy, together, act as a gravitational lens on the light from the more distant QSO. More direct imaging observations have led to the galaxy being located 1" north and 0~'19 east of the southern QSO image (ApJ 242, 1141). An expected 3rd QSO image may be nearly coincident with the galaxy. It has been proposed that flux variations may be expected due to intervention by the stars in the outer parts of the gravitator (Nature 282, 561; ApJ 244, 756). The time delay between the two images A and B should fall in the range 0.031.7 yr (ApJ 241, 1133). Recently, time delays of up to 5 yr have been proposed (ApJ 244, 736). A phenomenon similar to 0957+561A, B has been found in the triple QSO PG1115+08 (Nature 285, 641; 287, 416). It may be a quintuple gravitational lens image (ApJ"244, 723), one of the three components has also been resolved into two components by speckle interferometry (ApJ 248, L1). Brightness amplifications by undetected gravitational lenses could be responsible in part for the apparent evolution of quasars (ApJ 242, L135), particularly for those which appear to be of high luminosity. Even if lens events "are rare, a large fraction of them will appear more luminous than the most luminous unlensed quasars. The effects of gravitational lensing on the relation between QSO and galaxy magnitude- number counts have been treated by Tyson (ApJ 248,L89). Canizares (Nature, in press) has shown that the enhanced surface density of quasars brighter than a given threshold near a gal'axy may be due to gravitational focussing of light; there is no need to abandon the cosmological interpretation of the redshift in the cases where associations between QSOs and galaxies with discrepant redshifts appear. The BL 1ac objects More than 60 objects are now known to belong to this class. About 40 have been studied at 6 and 2 cm (MN 190,269). They have as a rule flatter spectral indices in this range than a general sample of radio sources. The peculiar outburst of BL Lac itself in 1975 has been described as an occultation phenomenon (AZh 57, 433) or as due to the structure of the emitting region (ApJ 227, 1117). The presence of periodic components in its light variation has been discussed (Pisma AZh 5, 403). Outbursts have been observed in a number of objects in optical and/or infrared wavelengths. In some cases correlations with radio outbursts are indicated. Typical objects are OJ 287 (AJ 84, 1253; Aph Space Sci 73, 263); B2 1308+326 (ApJ 227, L11; 235, 717); AO 0235+164 (ApJ 234,466; 236. 84; 240, L3); and 0846+51WI (ApJ 230,68). AO 0235+164 has recently been resolved into a very bright core and a jet-like component extending 5~14x10-3; 98 per cent of the total flux is contained within a diameter 36"x10- 3 (AA 96, 316). Similar VLBI observations of BL Lac showed a complex structure of several components. In the middle of 1980 15 BL Lac objects were known to be soft X-ray sources

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(ApJ 243,42). High energy X-ray observations of several BL Lac objects gave, with the exception for Mk 421, only upper limits in the energy ranges 25-60 and 60-130 keV (Ap Lett 20,63). Mk 421 belongs to the soft X-ray sources (ApJ 227,L63). The X-ray spectrum of PKS 0548-322 has been described (ApJ 233, L47). This object consists of an elliptical galaxy and a point source (ApJ 233,504). It has a ,variable X-ray spectrum (ApJ 243,53). Far UV observations have been obtained of a number of BL Lac objects: exemples are Mk 501 (MN 189,873); PKS 2155-304 (Nature 285,555); and 9716+71 (AA 100,1). The very weak emission lines seen in the spectra of several BL Lac objec-::.s show that, in general, these objects have rather low redshifts. nOHever, sO:Je 3L Lac objects have higher redshifts; MgII 2795, 2802 absorption lines are redshifted into the visual spectrum (see Ap.Lett. 20, 119). A few BL Lac objects have multiple absorption-line systems: 1309-216 shows strong CIV absorption at z 1.361, 1.489 and 1.491 (MN 191,61) and 0215+015 has 4 absorption syster.-J, Z 1.254; 1.345; 1.549 and 1.649 (Blades et al., MN in press; Gaskell, ApJ, in press). 5. REDSHIFTS (V.C. Rubin) The acquisition of galaxy and QSO redshifts continues at an accelerated pace as new detectors, larger telescopes, and novel observing techniques are employed. A comparison with the status only three years ago is interesting. Many more allsky, large scale surveys are underway presently, in order to answer questions about the motion of the Galaxy, the dynamics of clusters and superclusters, and the three dimensional distribution of galaxies. Because it is not possible to mention most of the thousands of pUblications since 1978 which report rew redshifts, the emphasis here will be on review which include extensive bibliographies, and some unpublished works. GALAXIES: Redshifts for all 1246 galaxies in the Revised Shapley-Ames Catalog (Sandage and Tammann, Carnegie Inst. of Wash.) are available. NGC 3285, the only galaxy lacking a velocity in the catalogue, has now been observed. Over 500 references to individual observations are included. A Catalogue of Galaxy Redshifts (CGR) (paper copy from Rood, lAS, Princeton, N.J. ;tape copy from J.M. Mead, NASA Goddard, Greenbelt, Md.) contains about 4000 redshifts for 'galaxies with V < 15,000 km/s, generally 0 > -2 0 30', blue magnitude brighter than 13, as well as hundreds of references. The CGR is based initially on Index of Galaxy Spectra (Gisler and Friel, Pachart Publ., Tucson, Az.), which lists redshifts published through Aug. 1978 and on the Ruchra (unpublished) Bright Galaxy Redshift Catalog. A valuable analysis of the errors in the CGR (Rood, ApJ Suppl, 1982) shows optical velocities to have typical rms uncertainties of 100 km/s, but with accuracy for individual studies ranging from 8 km/s to 800 km/s. With care, optical velocities can be as accurate as 21-cm velocities. A comparison of very high signal to noise single dish profiles for 26 Sc and Sb spirals with high resolution long slit Ha velocities referred to the nightsky OR bands yields ~(Vopt - V21 )= 0.23±7.5(10) km/s (Thonnard et al., 1982). Even as comprehensive catalogues are prepared, additional studies are completed. The following pUblications are tabulated to indicate the range of velocity programs: ApJ 229,73. 32 Southern Radio Sources Wright et al. ApJ Suppl 44, 137. 301 Galaxy Pairs Karachentsev PASP 92, 553. 22 Revised 3C Galaxies Smith and Spinrad ApJ Suppl 46,75. 172 S. Galaxies, companions Arp AA Suppl 43, 121. 25 Galaxies with Supernovae Balkowski et al. AA Suppl 44, 217. 457 HI galaxies Bottinelli et al. MNRAS 196, 417. 70 s. Compact Galaxies Fairall

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72 18 37 275

Gordon, Gottesman Kinman and Hintzen Wilkinson et al. West et al.

Blue Compact Galaxies Faint Haro Galaxies 4c Galaxies Uppsala Galaxies

323

AJ86,161. PASP 93, 405. MNRAS 196, 669. AA, in press.

A few of the major studies currently underway include the following: Bottinelli et al. C~incarin~, Haynes Glovanelll Green and Schmidt Osterbrock Spinrad Thuan Tifft West

J[

150 324 150 100 50 3C

Galaxies with outer rings Isolated Galaxies edge-on Sc Palomar Bright QSO Survey Suspected Seyferts Radio Galaxies

418 Dwarf Galaxies 370 Karachentsev doubles 500 Peculiar S. Galaxies

HI observations, 10% new HI,observations compL 75 new 14.5 35 M ), binaries or not, which have lost mass. They can be "runaway stars" in the s~cond WR phase. Several interesting stars have been discussed by Moffat and Seggewiss (1978, AA 70, 69; 1979, AA 77, 128; 1980, AA 86, 87), and Seggewiss and Moffat (1979, 343

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AA 72, 332). HD 197406 (WN7) is a single-line binary with a small mass function and a·'location 1000 pc from the galactic plane. The companion (z 4 M ) is probably the compact remnant of a supernova explosion which accelerated t~e system to its present location--a clear example of a runaway star. HD 197406 is apparently in the last phase of the evolutionary scheme for extreme Of binaries proposed by van den Neuvel: OB(1)+OB(2) - WR(1)+OB(2) - supernova - compact star +OB(2) compact star +WR(2). Two stars previously considered to be binaries have been found to be single stars: HD 151932, a member of Sco OBI with Mv=-6.S; and HR 93131. HD 92740 is a single-line binary which may be as massive as its companion, in contrast to several other WR+OR systems with mass ratios WR/OB in the range 0.2 to 0.4. Massey and Conti (1980, Ap J 242, 638) have found that HD 177230, considered a standard WN8 star, has a spectrum not resembling WN8, including the presence of hydrogen in the envelope. Further, it is apparently not a binary star. Among the early WN stars, HD S0896(WNS) and HD 192163(1'16) are of interest in that they are surrounded by ring nebulae (S 308 and NGC 6888 resp.). Van den Heuvel considers these stars to be in the second WR phase, which requires that they have compact companions. No evidence for binarity has yet been presented. Photometric, spectroscopic, and polarimetric variations of HD 50896 been discussed by various authors (Ebbets 1979, PASP 91, 804; Moffat and Seggewiss 1979, AA 77, 128; Firmani et al. 1980, IAU Symp 83, 421; McLean 1980, Ap J 236, L149; Cherepashchuk 1981, MNRAS 194, 755). A period of 3.763 d implies a close binary system with a companion of small mass (1.2 M ), which is probably a neutron star accreting material from the wind of the WNS ~tar. The radial velocity of HD 192163 is in accord with that expected for a runaway 0 star, and the variations of its line profiles and wavelengths suggest that the star is binary (Koenigsberger et al. 1980, Rev Mexicana Astron Astrof 5, 45). Several investigations have dealt with the properties of WC stars. HD 152270 (WC6-7+05), a member of the cluster NGC 6231, undergoes peculiar variations in the profile of the C III line, which Neutsch et al. (1979, Veroff Astron Inst Bonn, No. 92) have explained in terms of pertubations of the C III envelope by the hot star. The double-lined system HD 97152 (WC7+0B) has been discussed by Davis et al. (1981, Ap J 244, 528), who find the companion to have type 07V and obtain a mass ratio WC7/07 = 0.59 + 0.02; in good accord with similar systems in the galaxy. Sahade and van der Hucht (1980, Ap Space Sci 69, 369) have found flux variations in the region 2770-2870 A in y2 Vel (WC8+09I). Moffat and Seggewiss (1980, IAU Symp 88, 181) have given a list of WR binaries with established orbits, consisting of 12 double-line systems and 9 single-line systems. Apparently a maximum of 25% are WR+O binaries. Among the double-line system, the mass ratio is sensibly constant for WN and WC stars of different subclasses. This result imposes constraints on the hypothesis of the evolution of WN to WC stars with additional mass loss. The mass ratio is also independent of the orbital period. Among the single-line systems, primarily of class WN7, the mass ratio M(WR)/M(2) is larger than in the double-line systems. Williams et al. (1980, MNRAS 192, 25) find that the infrared (H-K) color indices of WR stars are strongly perturbed by emission lines, such that the observed differences between WC and WN stars in this index are due entirely to that effect. IR photometry demonstrates the presence of dust envelopes for late WC stars, but Williams and Allen (1980, Observatory 100, 220) find no evidence for dust around HR 115473 (WC5). However, an excess in H-K was observed by Allen and Puster in 1972, and a UV deficiency was noted by van der Hucht et al. (1979, AA Suppl 38, 279). Williams and Allen suggest that the star may have lost a thin dust envelope, as did HD 193793 (WC7).

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HD 50896 (WN5) and HD 191765 (WN6) have UV deficiencies and IR excesses beyond the predictions of the empirical model adopted for these stars. Van der Hucht et al. (1979, AA Suppl 38, 279) suggest that these stars have very extended envelopes and/or that they are enveloped in dust. The latter hypothesis is quite plausible, since these stars are in the centers of ring nebulae. The infrared spectra (8-13 ~m) of late WR stars have been studied by Aitken et al. (1980, MNRAS 192, 679), who found peculiarities in the spectra of WCIO stars. Two unidentified lines, not present in WC8-9, appeared, and, in general, the spectra resembled that of a planetary nebula. For WC8-9, the spectra could be interpreted as that of a blackbody at 900 K with absorption at 10 ~m due to grains of SiC. Such a temperature is too low for the WCIO stars. Underhill (1979), Ap J 234, 137; 1980, Ap J 239, 220; 1981, Ap J 244, 963) has discussed the relationship between 0 and WR stars. WN7-8 stars are situated on the HR diagram near the BOla stars, but beyond BO.5III. The temperatures of these stars are near 26000 K, in good accord with E Ori, BOla. She suggests that the WR state is a short phase in the evolution of a massive star. Many WR stars have been found in the Magellanic Clouds, and recently Conti and Massey (1981, Ap J, in press) have found 14 WR stars in M33, among which 6, enclosed in small H II regions, resemble galactic WR stars. The remaining, located in giant H II regions, resemble the superluminous WR stars found in 30 Dor, the LMC, and NGC 3063. Kunth and Sargent (1981, AA 101, L5) have found strong and broad emission lines in the spectrum of the dwarf galaxy Tololo 3, which they attribute to WR stars. 2.

Normal Stars of Types B-F -- J. Jugaku

2.1 B-type stars. Ultraviolet observations of early-type stars have yielded information on mass loss and on the adequacy of model atmospheres. Spectral atlases in the UV have been published by Meade and Code (Ap J Suppl 42, 283) for 132 stars, and for 1 Her (B3V) by Upson and Rogerson (Ap J Suppl 42, 175). Ultraviolet spectra have been compared satisfactorily with theoretical models except for early main-sequence stars and supergiants by Llorente de Andres et al (AA 100, 138). Dufton and McKeith (AA 81, 8) have observed He I lines for 29 stars 08-B7 and have compared with LTE and NLTE calculations. ~Iass loss characteristics displayed in UV spectra are discussed by Gathier et al. CAp J 247, 173), Hutchings and von Rudloff CAp J 238, 909), and Underhill (Ap J 235, L149). Studies of equivalent widths and line profiles in ground-based data have yielded information on abundances and non-LTE effects in B-star atmospheres. Heasley and Wolff CAp J 245, 977) have studied the 4922 A line of He I and found that the core and red wing agree with model predictions, but that the forbidden component in the blue wing is deeper and broader than predicted. Leparskas and ~Iarlborough (PASP 91, 101) have studied He II A4686 and C II A5696. Ebbets and Wolff CAp J 243, 204) have found the behavior of C III AA9701-9718 inconsistent with model calculations in 28 0 and B stars; the multiplet is in emission in stars earlier than 08. Dufton et al. (MNRAS 194,85) observed N II lines in 29 B stars, and, using NLTE calculations of line strengths, derived a N/H ratio agreement with the solar value. Thomas et al. CMNRAS 188, 19) have verified that the strength of the 0 I A7773 triplet may be used as a luminosity indicator in stars later than Bl. Evidence of autoionization and dielectric recombination in Si II in B stars has been presented by Underhill (AA 97, L9). Rotational effects in ultraviolet spectra have been discussed by Llorente de Andres and Duran (AA 72, 318), Hutchings et al. (PASP 91, 313), and by Kodaira and Hoekstra (AA 78, 292). It appears to be possible to recognize rapidly rotating pole-on B stars; ~ Cas and 1 Her may be examples.

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Bates et al. (MNRAS 190, 611; 195, 9p) have studied the supergiant S Ori (B8Ia) using IUE and balloon-borne observations. They have found evidence for an expanding shell photoionized by stellar radiation. The Bl supergiant Sl Sco has a UV spectrum dominated by blue-shifted resonance absorptions; there is weak evidence for a wind velocity up to 400 km/s (Appenzeller and 1I'01f AA Suppl 38, 51; AA 78, 15; and Hutchings Ap J 233, 913). Underhill (Ap J 239, 414) has determined effective temperatures, radii, and luminosities for several B supergiants, and has found that the rate of mass loss is not solely a function of luminosity. Dufton (AA 73, 203) has made an abundance analysis of the supergiants HD 96159 and HD 96261 and found a normal composition except for an 0.8-dex deficiency of nitrogen. Kane et al. (~lNRAS 194,537), on the other hand, found the B"l0.5Ia star lID 163181 to have a nitrogen excess by a factor 2 to 4, and to be underabundant in C and 0 by a factor of 5. They have interpreted the result as compatible with a star stripped to its convective core. Ambartsumian et al. (Ap J 227, 519) have observed P Cygni with a Copernicus satellite and found evidence for a wind with low terminal velocity and low ionization, unlike other B supergiants. The line profiles have been analyzed by ~ugis et al. (TAU Symp 83, 39), who have concluded that deceleration of the envelope may be present. Wolf et al. (AA 99, 351) have suggested that R81 (HDE 269128) in the LMC may be a close counterpart of P Cygni. Smith and Karp (Ap J 230, 156) have analyzed weak ultraviolet lines in T Sco and found a flow of material present in the deep photosphere, which may heat the chromosphere and corona. A study of UV resonance lines in T Sco by Hamann (~A 100, 169) has confirmed an outward decrease of ionization and yielded a mass loss rate of 10- 8 . 9 M /yr. Fraquelli (PASP 91, 501) has found rapid velocity and HS VIR variations iR HR 9070, and Wolstencroft et al. (MNRAS 195, 39p) have found evidence for a magnetic field in a Leo (B7V) from circular polarization measurements across the HS profile. Observations of B stars associated with X-ray sources include HDE 226868, which is suggested by several models to have a luminous companion. Shafter et al. (Ap J 240, 612) were unable to find evidence for such.a companion. HD 102567 (BIV), proposed counterpart of 4U 1145-61, has been observed with the IUE by Bianchi and Bernacca (AA 89, 214), who find evidence for an expanding envelope with a terminal velocity of 1800 km/s. 2.2 A-type stars. Line-profile changes in the spectrum of the supergiant a Cyg (A2Ia) have been studied by Inoue (PAS Japan 31, 11) and interpreted as due to temporary ejection of matter. A magnetic field has been detected in v Cep (A2Ia) by Scholz and Gerth (MNRAS 195, 853; Astr Nach 301, 211). Praderie et al (AA 86, 271) have derived mass loss rates from UV resonance lines in five supergiants and obtained rates less than that of a Cyg. The standard AOV star a Lyr continues to be the subject of investigations. Applications of new model atmospheres to UV and visible data have been carried out by Praderie et al. (AA 98,92); Hubeny (AA 98, 96); Castelli and Faraggiana (AA 79, 174); Sadakane and Nishimura (PAS Japan 31, 481; 33, 189); and Dreiling and Bell (Ap J 241, 736). Gray (PASP 92, 154) has analyzed the profile of five lines to obtain a projected rotation velocity of 23.4 km/s. The near-infrared absolute energy distribution has been obtained by Arkharov et al. (Astr Tsirk, No. 1046), and the visible energy distribution has been discussed by Kharitonov et al. (Astr Zh 57, 287). Abundances of B and Be in y Gem (AOV) were investigated by Boesgaard and Praderie (Ap J 245, 219), who found both elements substantially depleted (factor 4-10) relative to a Lyr. Dravins (AA 96, 64) found no evidence for chromospheric emission in the Ca II Hand K lines in 8 AV stars in the young cluster C0838-528

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and in the Hyades. Bohm-Vitense (Ap J 244, 938) found no differences in the energy distributions in the UV of slowly-rotating normal A stars and Am stars. 2.3 F-type stars. Boyarchuk et al. (22nd Liege Syrup, p. 361) have determined abundances in three F-type supergiants and found them solar except for Na. Luck (Ap J 232, 797) determined abundances in nine supergiants of types F-K. Atmospheric effects, including non-LTE and mass loss effects, in F supergiants have been studied by Sonnenborn et al. (Ap J 232, 807), and by Hopkinson and Humrich (MNRAS 195, 661). Gehren (AA 75, 73) has obtained [M/H] = -.51 to +.14 in seven near main-sequence field stars of types F6-GO. Bohm-Vitense and Dettmann (Ap J 236, 550) have used UV spectra of A-, F-, and G-type stars to discuss the boundary line in the HR diagram for stellar chromospheres. Other studies of chromospheric models and relevant~data for F stars include those of Brown and Jordan (MNRAS 196, 757), and Garcla-Alegre et al. (AA 96, 197). The latter paper demonstrates a Wilson-Bappu-type relationship for the Mg II emission line widths. 3.

Non-Variable Stars of Types M, C, S -- R. Viotti and M. F. McCarthy

The importance of UV observations in providing diagnostics of the outer atmospheres of cool stars has been demonstrated by several papers. Surveys of Mg II emission were published by Weiler and Oegerle (1979), Ap J Suppl 39, 537) and Basri and Linsky (1979, Ap J 234, 1023) who found that the ratio of Mg II surface emission to total flux is independent of luminosity. The UV spectra indicate the presence of a solar-type transition region in cool giants and supergiants earlier than type Kl, and of chromospheres only in cool stars (Linsky and Haisch 1979, Ap J 229, L27). Reimers (1980, ESA SP-157, 33rd) and van der Hucht et al. (1980, AA 82, 14) showed that absolute mass loss rates may be established from UV observations of cool giants with hot companions. A useful collection of papers may be found in the transactions of the conference, "The Universe at Ultraviolet Wavelengths" (1980, NASA: Greenbelt). The HEAO-2 survey of X-ray emission (Vianna et al. 1981, Ap J 245, 163) indicates that all dM stars show X-ray emission between 10 26 and 10 29 erg/s, which is probably correlated with multiplicity and emission-line behavior. Only upper limits are given for M giants and supergiants, confirming a decrease of the incidence of hot coronae in luminous stars of late type. Pallavinci et al (1981, Ap J 248, 279) show that the X-ray luminosity of G to M stars depends strongly on rotation rate, but not upon the bolometric luminosity. The circumstellar envelopes of M giants were studied by Boesgaard and Hagen (1979, Ap J 231, 128), wno found mass loss rates of 10- 9 to 10- 8 M /yr. Fe II shell emission in a Ori was studied by Boesgaard (1979, Ap J 232, ~85), and Linsky et al. (1979, Ap J Suppl 41, 47) reported a survey of Ca II chromo spheric profiles. Giampapa et al. (1981, Ap J 246, 502) derived chromospheric radiation loss rates from Ha and Na line profiles in M dwarfs; these imply a high degree of nonradiative heating of the upper atmospheres. Studies of line identifications and abundances in cool stars include a high resolution study of the violet spectrum of the cool carbon star 19 Psc by Peery (1979, PAS Japan 31, 461), and a study of the H2 bands in UU Aur and S Cep by Goorvitch et al. (1980, Ap J 240, 588). Titanium isotopic abundance ratios for cool stars are reported by Clegg et al. (1979, Ap J 235, 188); Dickens et al. (1979, Ap J 232, 428) determined C and N abundances in red giants in 47 Tuc; and the TiO strength in metal-rich globular clusters are studied by Mould et al. (1979, Ap J 228, 423). Molecular band identifications in S stars were carried out by Murty (1980, Ap J 240, 363 and 585), and by Lindgren and Olofsson (1980, AA 84, 300). TiH was identified in M stars by Yerle (1979, AA 73, 346). New molecular

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bands in S stars were also identified by Lambert and Clegg (1980, MNRAS 191, 367). Gahm et al. (1981, AA 98, 341) found low lithium abundances in ten luminous cool stars in reflection nebulae and young star clusters. Ake and Greenstein (1980, Ap J 240, 859) studied four low-metal abundance sdM stars with weak molecular bands and strong Ca I 4227 A and found that they are subluminous for their colors. Humphreys (1978, Ap J Supp1 38, 309; 1979, 39, 389; 1979, Ap J 231, 384) studied the spectra of the brightest M supergiants in the Milky Way and in the Magellanic Clouds. The maximum visual luminosity is near Mv=-8 in the DIC and the Galaxy, but no stars later than MIl were found in the SMC. The lower metallicity of the SMC may produce a shift to earlier spectral types through lower atmospheric opacity. Richer (1981, Ap J 243, 744) studied spectroscopically and photometrically a complete sample of 71 carbon stars in the LMC and derived a surface density 10 to 50 times higher than in our Galaxy. SMC carbon stars may be a few tenths of a magnitude brighter than those in the LMC. An SC star was identified in the LMC by Richer and Frogel (1980 Ap J 242, L9). Mould and Aaronson (1980, Ap J 240, 464) found carbon stars and 1>1 giants with luminosities appropriate to the upper asymptotic giant branch in red globular clusters in the LMC and SMC. A similar result was derived by Frogel et al. (1980, Ap J 239, 495). These results, which are contrary to theoretical expectations, have been discussed by Iben (1981, Ap J 246, 278). After the pioneering work of Demers and Kunkel (1979, PASP 91, 761), carbon stars and late giants have been detected in the Fornax, Sculptor, Draco, and Carina dwarf galaxies; many of these stars have bluer colors, as do those in the SMC, compared to galactic stars (Aaronson and Mould 1980, Ap J 240, 804; Westerlund 1979, ESO Messenger 19, 7; Frogel et al. 1981, Ap J, in press; Aaronson 1981, BAAS 13, 506; Cannon et al. 1980, MNRAS 196, lp). A catalog of Sand SC stars on the revised MK system was prepared by Keenan and Boeshaar (1980, Ap J Suppl 43, 374) giving estimates of ZrO, TiO, and YO band strengths, and Na and Li lines. 4.

Interacting Binary Systems -- K. O. Wright

4.1 The ~ Aurigae stars. The VV Cephei eclipse of 1976-1978 has been analyzed by ~1011enhoff and Schaifers (1980, AA 94, 333), Kawabata et al. (1981, PAS Japan 33, 177), Saito et al. (1980 PAS Japan 32, 163), and Saijo (1981, PAS Japan 33, in press). They find that the emission lines at Ha and HS can best be explained by a flattened rotating envelope (300-400 R ) surrounding the early-type secondary star; the radius of the M-type primary starOis 1700-1900 R. Mideclipse occurred at JD 2 443 360 confirming the 7430-day period. lUg spectra of VV Cep have been obtained by Faraggiana (1980, IAU Symp 88, 549) and Hagen et al. (1980, Ap J 238, 203); the Mg II lines have different shapes but show chromospheric emission and indicate an expanding atmosphere for the M-type star. Stencel et al. (1979, Ap J 233, 621 analyzed IUE spectra of 32 Cygni. All UV resonance and strong lines show P Cygni profiles and multiple absorptions with velocities up to 400 km/s, twice as large as observed for the K line. The B6 star probably lies within the atmosphere of the K5 supergiant and, as a result, moving shocks may be set up in the atmosphere. The mass loss rate is 4 x 10- 7 M_/yr. 32 Cyg was studied extensively at the 1981 eclipse by Stencel et al. (privace communication) with the IUE, and preliminary analysis shows that the temperature increase with height in the upper chromosphere, observed at optical wavelengths, continues in the ultraviolet.

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4.2 Interacting binaries: Algols and longer periods. IAU Symposium 88 provides an excellent survey of close binary research in 1979. Algol has been studied by Soderhjelm (1980, AA 89, 100), who concluded that the secondary component fills its Roche lobe, that period changes show that mass and angular momentum are lost, and that the 32-yr period may be a magnetic cycle. Rucinski (1979, Act Astr 29, 339) studied the rotation of the primary star using the N II 1075.5 A line and concluded that rotation and orbital motions are synchronous. White et al. (1980, Ap J 239, L69) observed Algol with Einstein; there was no xray eclipse, indicating that emission probably comes from an active corona surrounding the K star.

S Lyrae continues to be studied extensively. Sahade (1980, Sp Sci Rev 26, 349) provided a general review of the system; it is rapidly evolving and the B8 star now fills its Roche lobe. Plavec (1980, IAU Symp 88, 251) contends that the W ser stars RX Cas, SX Cas, V367 Cyg, W Cru, S Lyr, a~g W Ser_~re related, as shown by IUE observations, with mass transfer from 10 to 10 M /yr; color temperatures in the UV are higher than in the optical region, and~strong emission of N V, C IV, Si IV, Fe III, Al III are present; these phenomena are the result of accretion onto nondegenerate stars. Kondo et al. (1979, Ap J 233, 906, 1980, IAU Symp 88, 237) found that IUE spectra of U Cep showed broad lines of Si II-IV, Al II-III, etc., associated with the B star, which, from their variable absorptions, suggest hot spots and gas streaming. The secondary spectrum of U Cep was studied by Parthasarathy et al. (1979, MNRAS 186, 391), who found that the s-process elements had normal abundances, and that the data indicate an active chromosphere as a result of tidal effects. 4.3 Contact binaries: W UMa Stars. Carroll et al. (1980, Ap J 235, L77) identified VW Cep with a faint X-ray source that shows some variation of flux with phase. Dupree (1981, Cent Ap Prepr 1433) discusses chromospheres and coronas in 44 Boo, VW Cep, and s CrA; UV spectra show lines of C II, Si IV, C IV, and N V. In the X-ray region there is a relation between luminosity and period, but the Xrays are not always in phase with the optical variation. Mochnacki (1981, Ap J 245, 650) studied 37 W UMa systems, and concluded that the A-type stars are more evolved with lower angular momentum and density than W UMa, possibly as the result of stellar winds and magnetic braking. 4.4 RS CVn stars. The unresolved problems of these systems, which show surface activity and photometric pecularities, were discussed by Hall at the 1979 General Assembly (1980, Highlights Astr 5, 841), including the relative importance of rotation and duplicity, and the significance of spots in producing the photometric moving wave. Walter et al. (1980, Smithsonian Spec Rep 389, 35) discussed HEAO-l X-ray observations and concluded that there are two types of coronae in these systems; the most extreme activity found in short-period systems may be the result of rapid rotation and magnetic flux in the convective zone. The discovery of radio flares in HR 1099 resulted in an international campaign of UV, optical, and radio observations for HR 1099 and UX Ari (Weiler et al. 1978, Ap J 225, 919); variable Ha emission was observed by Bopp (1979, IBVS 1669) and by Nations and Ramsey (1980, A J 85, 1086); Ca II Hand K and hydrogen line variations were studied by Oswalt (1979, PASP 91, 222). Simon and Linsky (1979, Ap J 24, 759) analyzed emission line profiles in HR 1099 and UX Ari and found that the fluxes could be reproduced with a chromosphere of low surface pressure. Swank and White (1980, Smithsonian Spec Rep 389, 47) found that X-ray observations could be fit with a two-component model: a high temperature, large-volume component which is not eclipsed, and a lower-temperature component that might be associated with a star spot.

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4.5 X-Ray binaries. Crampton (1980, IAU Symp 88, 313) has summarized the data on these systems, especially from the optical viewpoint. Cyg X-I, Cir X-I, and GX 339-4 are the most probable candidates for black holes. HZ Her = Her X-I has been studied in the UV by Kippenhahn et al. (1980, IAU Symp 88, 349), by Joss et al. (1980, Ap J 235, 592), and by Gursky et al. (1980, Ap J 237, 163). Strong emission lines of N V and C IV vary with phase, the ratio N VIC IV being 2 at phase 0.5 and 1 near eclipse; they probably arise from both the heated photosphere and the accretion disk. De Loore et al. (1979, ~~ 78, 287) organized a coordinated X-ray and groundbased campaign for X Per in 1977; there was a less marked Balmer excess than in 1971-1972, weaker emission than in 1970, and a double-peaked Ha emission; Mufson et al. (1980, BAAS 12, 500) found a rapid variation in Ha. Bernacca and Bianchi (1981, AA 94, 345) found a good fit for the 1000-1900 A continuum for Te = 30000K; Si IV and C IV resonance lines indicate the presence of a variable envelope. 4.6 AM Her stars. AM Her systems are close binary stars with a mass-losing nondegenerate star and a magnetized accreting degenerate dwarf. The AM Her system has been reviewed by Chiapetti et al. (1980, Sp Sci Rev 27, 3) with its 3.1-h period observed from X-ray to infrared frequencies and in linear and circular polarization; the results of such simultaneous observations were given by Szkody et al. (1980, Ap J 241, 1070). ruE observations by Raymond et al. (1979, Ap J 230, L95) showed strong emissions from 0 I to N V; similar data were presented by Tanzi et al. (1980, AA 83, 270). A thorough study of AM Her was made by Crosa et al. (1981, Ap J 247, 984), who derived a model involving accretion on both magnetic poles of the white dwarf: the X-ray and optical radiation come from different poles which are of different strengths. 4.7 SS 433. Crampton et al. (1980, Ap J 235, L131) observed a 13-d binary period and deduced masses 20". Large-scale properties of the galactic halo will be discussed in Section 4D. A number of studies have been made in the region of the South Galactic Pole. Guseva (26.155.074) has studied stars of class B7-G4 and also dust, Yoss and Hartkoff (26.113.015) have investigated the K-giant population, Blaauw (22.113.026) has discussed the faint F stars, Pesch and Sanouleak (22.155.030) have compiled a catalog of probable dwarf stars of type M3 and later, and Eggen and Bessell (22.126.029) have searched for white dwarfs. Elias (22.133.001) has discussed the properties of all the 2.2~ field stars seen near the North Galactic Pole, and shows that they can all be identified with stars of known spectral types. Clube (22.112.004) has reanalysed some absolute proper motions of faint M stars in the region of the North Galactic Pole, and obtained some support for a higher space density of M stars. Hill et al. (25.155.013) have studied A & F stars in the region of the North Galactic Pole and have redetermined the local mass density at 0.108MQpc- 3 • Interstellar reddening towards the South Galactic Pole has been discussed by Albrecht and Maitzen (28.131.081), while Markkanen (25.131.099) has used polarimetric observations of 70 stars near the North Galactic Pole to determine a lower limit of interstellar extinction in this area of Om03. King et al. (26.134.004) have found a very extensive nebulosity of low surface brightness in the region of the South Celestial Pole. They suggest it is predominantly reflection nebulosity, in a layer at 40-80 pc below the local galactic plane. REFERENCES Forte, J.e., and Orsatti, A.M.: 1981, Astron. J. 86, p.209. Kerr, F.J., Bowers, P.F., and Henderson, A.P.: 1981, Astron. Astrophys. Supp1. Ser. 44, p .63. Kilkenny, D.: 1981, Mon. Not. R. Astron. Soc. 194, p.927. Martinez, R.E., Muzzio, J.C., and ~Jaldhausen, S.: 1980, Astron. Astrophys. Suppl. Ser. 42, p.179. Vader, J.P., and de Jong, T.: 1981, Astron. Astrophys. 100, 124. Vega, E.I., Rabolli, M., Muzzio, J.C., and Feinstein, A.: 1980, Astron. J. 85, 1207. Hramdemark, S.: 1980, Astron. Astrophys. 86, 64. 4. OVERALL STRUCTURE OF THE GALAXY A. General Observational Surveys The triennium saw the completion of two surveys of the southern-sky HI emission. The surveys of Cleary et al. (25.155.015) covered a < -30", excluding the strip at ibl < 10" which was surveyed by Kerr et al. (1981, A & A Supp1.). Heiles and Cleary (26.131.106) published column densities of the southern HI. Synoptic views of the combined northern and southern data were published by Cleary et al. (25.155.015) for ibi > 10", and by Valdes (22.155.008) for ibi < 2". A photographic presentation of the Argentine data combined with the Hat Greek survey at ibi > 10" 'vas published by Colomb et a1. (27.155.008).

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

Franco and Poppel (21.131.116) observed the field 348° < ~ < 12°, 3° < b < 17° and interpreted the data in terms of Gould Belt kinematics.

Olano and Poppel (1981) likewise interpreted HI data of the region 320° < ~ < 341°,7° < b < 26°, in terms of the Gould Belt. Braunsforth and Rohlfs (21.002.038) observed the disk at Ibl < 1°5, 20° < ~ < 42°. Poppel et al. (27.002.059) published an atlas of low-latitude southern HI. Absorption by galactic HI was studied towards 819 sources by Crovisier et al. (21.002.039). Self-absorption characteristics of galactic HI were studied by Baker and Burton (25.155.002). Several surveys of low-latitude 12CO emiss;on were published. The material of Burton and Gordon (21.155.004) covers emission at b = 0°, 10° < ~ < 82°. The surveys of Solomon et al. (26.155.018) and Cohen et a1. (26.155.019, 28.131.202, 28.155.014) provide more extensive coverage, especially in b. The analyses of these surveys stress galactic morphology. Liszt and Burton (Ap.J. 236) discussed aspects of the interpretation of CO emission from the ensemble of molecular clouds. The isotope l3CO was studied by Solomon et al. (26.155.005), with an analysis which stressed morphology, and Liszt et al. (Ap.J. 249), with an analysis which stressed length scales. A large-scale OH sky survey at 1612 MHz was published by Bowers (21.131.024, 21.122.063). An extensive survey, on an irregular grid near the galactic plane, of all four 18-cm OH lines was published by Turner (25.002.035). Baud et al. (25.131.080) published a systematic search at 1612 MHz for OH maser sources between 10° < ~ < 150°, Ibl < 4°; the galactic distribution of OH/IR stars derived from this survey was discussed by Baud et al. (26.155.017). Observations of H2CO along the galactic equator at 8° < ~ < 60° were published by Few (25.155.018) and additionally discussed by Davies and Few (26.131.066). Downes et al. (27.141.133) surveyed 262 galactic sources in the HllQl line and in the H2CO absorption line at 4.8 GHz. Radio observations of the galactic plane CH distribution at 10° < ~ < 230° were reported by Johansson et al. (26.155.020). Genzel and Downes (25.131.024) interpreted H2CO data in a galactic context. Nonthermal emission observed at V < 10 MHz by satellite was reported by Novaco and Brown (21.156.009). Haynes et al. (22.002.031, 26.141.094) published a survey of the southern plane at 5 GHz. A survey of the plane at 4.875 GHz was made by Altenhoff et al. (25.141.002) from Effelsberg. A 2l-cID continuum survey of the regi.on 93° < ~ < 162°, Ihl < 11°, was carried out with the 100-m telescope by Kallas and Reich (28.156.006). A summary of the continuum surveys made with that telescope was given by Downes (26.156.008). A correlation between discrete sources and the structure of the galactic background radiation was discussed by Larionov and Sidorenkov (21.141.116). Brindle et al. (22.156.002) gave a three-dimensional model of the galactic continuum emissivity. Wielebinski (25.156.009) reviewed the nonthermal radiation in terms of SNR's and pulsars. Using the nonthermal radio spectrum, Webber et al. (27.156.001) reexamined the interstellar electron density. Several balloon surveys of IR radiation from the galactic disk were made during this triennium. Fazio (26.133.019) reviewed the results. Mahaira et al. (21.155.011) scanned the area 350° < ~ < 27°, Ibl < 10° at 2.4 ~m. The near-IR surface brightness of the southern plane was studied by Hayakawa et al. (25.155.027). Mahaira et al. (25.156.003) amd Okuda et al. (26.156.012)

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observed the diffuse far-infrared and derived a surface-brigtbness distribution of the plane at 340 0 < 9., < 22 0 • Owens et al. (26.156.003) surveyed much of the sky with a large beam at mm and sub-mm wavelengths. Drapatz et al. (28.156.014) reported balloon-borne observations at A > 50 ym of the inner Galaxy. Hoessel et al. (25.156.008) carried out a near-infrared survey of the plane using the 1.2 m Palomar Schwidt. The far-infrared emission from clouds was studied by Ryter (25.131.085). Drapatz (25.156.009) summarized properties of the Gisk consistuents in deriving the far-infrared diffuse emission as a function of longitude. Serra et al. (26.156.006) presented a longitude profile of the far-infrared diffuse emission. Viallefond et al. (27.156.002) scanned an area of the galactic disk from an airplane, and demonstrated a correlation between the far-infrared and the radio-continuum emission. Nishimura et a1. (28.156.005) mapped from 9., = 352 0 to 45 0 in the 100 - 300 ym band; they related their data to HIl and CO sources. The near-infrared surface brigthness of the galactic anticenter was observed \vith a rocket-borne telescope by Hayaka\Va et al. (22.156 .00y). Becker (22.155.012) reviewed the use of optical material as a tracer of galactic structure. Parker et al. (27.002.011) published an emission-line survey of the Milky \lay. The color distribution of the integrated spectrum of the Milky Hay was surveyed by Kostyakova (21.155.005). Hanner et aI. (21.155.022) used the Helios probe to measure the UBV brigthness along four strips through the Milky Way. Mattila and Scheffler (21.155.026) analysed fluctuations in the diffuse galactic light in a study of the statistical parameters of interstellar clouds. Lucke (21.131.119) correlated the distribution of reddening material with the Gould Belt. Lynga reviewed the relationship of dust to galactic structure, based principally on latitude variations of extinction. Several investigations dealt with uv-observations of tr.e diffuse galactic light. Morgan et al. (22.155.027) derived the alr.edo of interstellar dust from satellite data in the range 1550-2740 A. Henry et al. (21.157.007) scanned the far-uv and interpreted the data in terms of a hot, extragalactic plasma. UV scans in the vicinity of the 0 IV transition were interpreted by Jenkins (21.131.019) in terms of a hot galactic corona. The contribution to the interstellar uv-radiation from diffuse galactic light was studied by Gondhalekar et al. (27.157.003). A correlation of the uv radiation background "lith HI column density led Maucherat-Joubert et a1. (28.157.002) to conclude that a significant portion of the diffuse uv is of galactic origin. Paresce et al. (28.142.053) discussed possible systematic contamination of far-uv background data. Caplan and Grec (26.155.013) and Mattila (27.155.009) incorporated clumping of the interstellar dust into a model of the Milky Hay disk. Grey-scale maps of the diffuse galactic Ha emission constructed by Reynolds (27.155.002) showed filamentary structures extending ~ 1 kp from the galac tic plane. Zavarzi n (22.155.048) pubU shed isophote maps of the ~Iiny Hay constructed from photometry in the R system.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

B. Overall Structure The triennium saw efforts to refine the inner-galaxy rotation curve and to determine the rotation parameters of the outer galaxy. Grape (22.155.039) took into account asymmetries in the HI distribution in suggesting rotation and expansion velocity fields at R < 5 kpc. Sinha (22.155.019) reexamined the rotation curve for R < 10 kpc by including southern and northern HI data and data at b = 0°. ~he apparent north-south asymmetry of the rotation curve was discussed by Jaakkola et al. (22.155.035) in terms of a general expansion of spiral arms rather than of the galactic disk itself. Petrovskaya (26.155.065) derived from HI profiles rotation curves separately for the first and fourth quadrants, assuming pure rotation. Haud (25.155.031), on the other hand, favored a rotation curve corrected for a general expansion of the gaseous disk. Burton and Gordon (21.155.004) compared the rotation characteristics at R < Ro derived from CO observations with those derived from the more diffuse HI gas. The rotation parameters at R > Ro were the subject of several investigations. Using HI data, Knapp et al. (22.155.044) and Gunn et al. (26.155.011) found a linear curve near Ro and lower values of the constants Ro and 8 0 than usually adopted. Jackson et al. (26.11.008) and Moffat et al. (26.113.021) based their study of the outer-galactic structure on photometry and spectroscopy of 0 and B stars associated with HII nebulosities. Blitz (26.155.003) and Blitz et al. (28.155.027) used velocities from CO observations of Sharpless HII regions of known distances in order to determine the rotation curve to R ~ 17 kpc. Many studies during the triennium were directed toward the galactic distance scale and the fundamental kinematic constants. Reviews of some of the recent accumulated evidence on 8 0 were given by Knapp (26.155.028), who favored 0 0 = 220 km s-l, and by Einasto et al. (26.155.029). Loktin (26.155.067) derived a value Ro = 8.1 kpc from data on 235 0 and B stars. Surd in (28.011.018) introduced a method to determine Ro based on the dependence of the metallicity of globular clusters on R. Quiroga (28.155.041) based a determination of Ro on comparison of kinematic distances of HII regions ana photometric distances of their exciting stars. Celnik et al. (25.155.032) offered a determination of the thickness of the galactic disk based on HI observations. The displacement of major structures from the plane b = 0° was studied by Kolesnik and Vedenicheva (25.155.033) for the case of 0 and B stars, by Lockman (25.155.025) for the case of HII regions, and by Cohen et al. (28.155.014) for the case of CO clouds. The length scale of the exponential disk of the Galaxy was discussed by de Vaucouleurs (26.155.060, 26.155.027); the latter paper is a useful review of the morphology of our system. Edmunds (26.155.004) reviewed the abundance gradient problem. Evidence for a gradient of stellar metallicity in the galactic disk was given by Janes (21.155.053, 25.155.021), by Kraft et al. (26.155.050), and by Marsakov and Suchkov (27.155.006). Panagia and Tosi (27.155.005) based discussion of the chemical gradient on analysis of the H-R diagrams of open clusters. Chiosi and

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Matteucci (27.155.027) and Dluzhnevskaya et al. (27.155.026) discussed this problem also. Butler et al. (26.122.025) dealt with the metal abundances of RR Lyrae stars in different parts of the Galaxy. Penzias (22.131.086) reviewed the relative abundances of the common elements and concluded that the distribution are rather uniform. Churchwell et al. (22.132.036), on the other hand, presented evidence for a gradient of HII region electron temperatures and helium abundance. Evidence for abundance gradients based on spectrophotometry of HII region emission lines was given by Peimbert et al. (21.132.013). Smith et al. (21.131.172) discussed star formation rates in the galactic disk. Mallik (21.131.252) discussed nitrogen enrichment across the Galaxy in the context of planetary nebulae observations. Perspective on Milky Way studies can be gained by comparisons of our system with other systems. Humphreys (26.155.022) compared the distribution of young stars, clusters, and associations in the Milky Way with the distribution in ~33; Talbot (27.155.001) compared various aspects of M83 with our Galaxy. de Vaucou1eurs and Pence (22.155.031) compared photometric parameters of our Galaxy with those of other galaxies. Comparative studies of the distribution in the Galaxy of interstellar gas and different tracers of star formation were given by Guibert et a1. (21.155.051), by Quiroga (21.131.136), and by Voroshi10v and Ka1andadze (28.155.028). Galactic structures as revealed by optical methods was discussed by Kostyakova (21.155.006); by Guibert et al. (21.155.051), who compared the disk thickness of young populations; by Spaenhauer and Fenkart (25.155.003), who derived the space density of late-type giants; by Lynga (27.155.024) for stars in clusters and associations; by Pav10vskaya and Suchkov (27.155.039) for cepheids; and by Lynds (28.155.001) for 0 stars. Attempts to derive the galactic distribution of HI were described by Petrovskaya (22.155.059), Berman and Mishurov (27.155.042), Sawa (21.155.021), and Petrovskaya and Korzin (28.155.032). Kerr's (26.155.021) review of this problem incorporated the new southern HI data. Analyses of recent CO surveys by Scoville et a1. (26.155.033), Cohen et a1. (28.155.014), and Liszt and Burton (Ap.J. 236) offered different interpretations of the galactic distribution of molecular clouds. Galactic morphology as presented by OH/IR sources was reviewed by Habing (21.155.018). Puget et a1. (26.155.024) and Serra et a1. (27.156.003) derived the IR emission of the Galaxy as a function of ga1actocentric distance. Weaver (26.155.034) and Ariskin (26.155.059) described the role played by supernova remnants as common features of the disk. The morphology of the North Polar Spur was studied by Hei1es et a1. (28.155.045) as an example of a giant HI shell. The structural aspects of the Galaxy within several kpc of the Sun were studied using both radio and optical tracers. The Perseus arm feature received attention in papers by Sparke and Dodd (21.155.001) on photographic photometry, by Gosachinskij and Rakhimov (21.155.008) on the A2l-cm line, by Birkinshaw (21.132.002) on 5 GHz maps of HII regions, by Grayzeck (25.155.017) on Cepheids, and by Yuan and Dickman (26.155.025) on the,CO distribution.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

C. The Inner Core of the Galaxy Observations made during the triennium over a wide wavelength spectrum advanced our knowledge of the kinematics and distribution of material in the nucleus of our Galaxy. Several papers serve as reviews of subject. Comparisons between the properties of our galac~ic nuleus and nuclei of other normal galaxies were made by Weedman (26.155.046), by Ekers (28.155.023), and by Liszt (28.155.024). A discussion of the properties within 300 pc of the galactic center was given by Audouze et a1. (26.155.064); Geba11e (25.155.039) reviewed the properties of the central parsec. Oort (21.155.024) reviewed the evidence for eruptive phenomena near the galactic center. Bania (26.155.038, 28.155.042) studied the latitude and longitude variation of the 3-kpc arm as outlined by CO emission and concluded it is not a symmetric ring structure. Lockman (28.131.139) traced H166a recombination line emission throughout the arm and determined that it is not a site of active star formation. The neutral gas within several ki10parsecs of the galactic center is tilted in a systematic manner with respect to the galactic equator. This conclusion gained support from the work of Cohen (26.155.036), Cohen and Davies (25.155.008), Sinha (26.155.007, 26.155.037), Burton and Liszt (22.155.029, 26.155.036, 28.155.048), and Liszt and Burton (22.155.041, 26.131.079, 27.155.012). The distribution of OH sources in the core of the Galaxy was discussed by Baud (21.133.028), and Baud et a1. (25.131.010,26.155.017). Information on the kinematics of gas in the central parsec was given by the IR spectroscopy of Dain et a1. (21.132.017), Lacy et al. (25.155.001, 28.155.021), Willner (21.156.002), Lacy (28.155.025), and Watson et a1. (28.156.008). The most probable mass distribution derived from IR line emission includes a central point mass of several x 10 6Mo • Hollman (26.156.011) reviewed the information given by infrared spectroscopy about the structure and energetics of the galactic center. Discussions on the possible existence of a massive black halo at the galactic center were given by Ozernoy (21.155.048, 26.155.044), and Paczynski and Trimble (26.155.045). The radio continuum structure of the compact sources in the central region was mapped by Downes et a1. (25.141.001). Information on the sub-pacsec scale revealed by spectroscopy at the infrared wavelengths was supplemented by information on the scale of a few hundred parsecs revealed by mm-wavelength observations of various molecules. Davies and Cohen (21.155.047) and Gusten and Downes (28.155.049) gave brief reviews of the motions of the molecular gas in the galactic center. Hhiteoak and Gardner (26.156.001) reported on an H2CO survey of the inner 4 degrees, which showed the extended cloud complexes also seen in HI and CO surveys. Bieging et al. (28.131.111) mapped the 4.8 GHz H2CO absorption in the region of the Sgr molecular complex; Gusten and Downes (27.131.183) interpreted these data in the context of expanding features. Fukui et a1. (28.131.133) observed the 3.4 mm line of HCO+ toward the Sgr complex. Fukui (28.131.203, 28.155.026) suggested a model involving a fan-shaped gas jet from the nucleus to account for these observations.

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Several extensive surveys of emission from hydrogen recombination lines contributed to understanding of the nuclear kinematics and temperatures. Mezger and Pauls (26.155.039) reviewed the thermal component of the cm-wavelength continuum emission in the context of star formation in the core. Pedlar et al. (21.156.001) observed low-frequency recombination lines in the direction of the center. Pauls and Mezger (27.156.007) mapped the recombination line radiation from the arc-like galactic center source and found that emission near -40 km s-l dominates. Hart and Pedlar (28.156.010) tnvestigated the thermal structure of the nuclear gas using recombination lines and concluded that evolved HII regions contribute to a nuclear haze of ionized gas. Rodriguez and Chaisson (22.156.001) interpreted reconbination line observations from Sgr A in terms of a core-halo model. Bally et al. (25.155.029) and Neugebauer et al. (21.156.005) discuss the arrangement of the nuclear clouds in terms of near-IR observations of the hydrogen ba and By lines. There was extensive observational activity in the infrared continuum during the triennium. Rieke et a1. (21.156.008) discussed ground based and airborne observations between 10 and 56 ~m. \,illner et al. (25.156.007) derived the 4 to 8 ~m spectrum of the center. Gatley et al. (21.132.014) discussed far-infrared observations within 1° of the center; their results are consistent with HII regions ionized by early-type stars. Andriesse and de Vries (22.155.004) analyzed data on the far-IR emission from dust near the center. Horking in the near-IR, Hofmann et a1. (22.156.013) mapped the central region using a balloon-borne detector. Hough et al. (22.156.011) discussed polarization observations in the near IR in terms of aligned grains. Kobayashi et al. (28.156.001) mapped the 2.2. ~m polarization of the central 7'. Oda et al. (25.155.016) mapped the 2.4 vm brightness distribution of the central region with a resolution of 0°6, and interpreted their data in terms of the dust distribution. The well-known 2.2 ~m map of the central 1° published by Becklin and Neugebauer (25.156.001) indicated the position of highest stellar density in the Galaxy. Bailey (27.155.003) derived a power-law variation of the central density. Liller and Alcaino (27.155.040) cataloged IR-bright stars in a region centered on the nucleus. UBV photometry of the nuclear bulge by Loibl et a1. (21.155.017) showed the variation of red giant density near the center. McCarthy et al. (28.156.015) observed 16-30 ~ID spectra of the Sgr A region and interpreted them in terms of the dust extinction and ionization structure of the gas. Harris et al. (28.156.007) showed by comparing CO profiles with 2.4 ~m features that the IR data could be interpreted in terms of inhomogeneities in the interstellar extinction. Becklin et al. (21.133.014) derived the 1-2 ~m extinction law from IR observations of compact sources. The nature of these sources was the subject of a paper of Becklin et al. (21.l33 .002) . Submillimeter observations at 540 (21.156.003) •

~m

were reported by Hildebrand et al.

D. The Outer Reaches of the Galaxy A review of the plausible properties of a halo component was given by Ostriker and Caldwell (26.155.048). Castellani (21.155.050) reviewed the chemical properties and age of the constituents of the halo. I!oltjer (22.155.021) reviewed evidence relating to the mass of the halo. Kraft et al.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

(26.155.050) reviewed methods by which metal-abundance gradients of halo stars can be obtained. Stecker (26.155.051) and Fichtel et al. (26.155.052) reviewed the y-ray evidence for a galactic halo; Ginzburg (26.155.053) reviewed the relevant cosmic ray data. The nuclear bulge component of the Galaxy was studied by Loibl (22.155.003) by means of photometry of late giants. ~)hitford (22.155.040) published scans of the integrated light from the bulge, and compared the situation in our Galaxy to that of external galaxies. Bregman (27.155.023) postulated a bulge wind to account for the deficiency of neutral gas in the disk at R < 4 kpc. Ostriker (21.155.057) also discussed several aspects of the interaction between halo and disk components. Hebster (22.156.014) analysed measurements of the galactic background radiation for information on the shape and size of the radio halo of the Galaxy. Saha et al. (22.155.002) gave a theoretical discussion of the plasma component of the halo. The signature of the radio halo at 38 and 404 MHz was studied by Milogradov-Turin and Ninkovic (27.156.010). Becker (27.155.053) studied the distribution of metal-poor stars in the halo. Bahcall and Soneira (27.155.044) investigated the possibility of detecting a halo component with the aid of star counts. Van den Bergh (25.154.009) showed how the apparent flattening of the galactic globular cluster system is affected by extinction. Harris and Canterna (25.154.027) investigated the gradient of heavy-element abundance in the halo. Mass exchange between the halo and the disk resulting from supernovae was studied by Chevalier and Oegerle (25.155.010). Sturrock and Stern (27.155.053) suggested that the halo might be heated from flares produced by distortions in the disk magnetic field. Nikhajlov and Syrovatksij (27.155.038) discussed the influence of the halo magnetic field on the arrival directions of high energy particles. Lipunov (26.156.020) identified the radio halo with a magnetosphere of the Galaxy. 5. KINENATICS A. Stars I. Galactic Rotation A colloquium on European satellite astronomy was held in 1978. "he improvement of stellar kinematics that could be expected from data obtained by an astrometric satellite was pointed out by Creze (25.155.048), Grosbol (25.155.047) and others. Lindblad (28.111.015, 28.155.016) discussed the information about galactic structure and dynamics that can be obtained from studies of local kinematics. Lin et al. (22.155.011) analyzed the observational determination of Oort constants and other Nilky vJay constants in the light of the density wave theory. Models of the solar vicinity are tested. From the accumulated current evidence Knapp (26.155.028) finds the circular velocity at the Sun = 220 km s-l and Ro = 8.5 kpc.

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Relative proper motions for 1300 low galactic latitude stars have been derived by Stone (26.111.002), who determined the solar apex and the mean secular parallax for these stars. Tsioumis and Fricke (25.151.069) investigated the velocity field of Gould Belt stars using data given by Lesh. Clube and Dawe (27.111.004) give a mathematical maximum likelihood model for determinations of stellar distances from proper motions and radial velocities. This technique is applied to RR Lyrae and Cepheid stars by Clube and Dawe (27.111.005). The galactic constants Ro, 9 0 , A and Bare derived. Stock (27.155.062) informs that the Merida program for radial velocity determinations from objective prism plates so far has produced data for 5870 stars. This material will permit statistical treatment concerning kinematical characteristics of the Galaxy. In order to improve the knowledge of the galactic rotation curve, Moffat et al. (26.113.021) observed OB stars in the netghborhood of H II regions obtaining UBV photometry, spectrograms for MK-classification and radial velocities. The aim is do derive distances for distant objects. Jackson et al. (26.111.008) used this material to construct a galactic rotation curve for R > Ro. Rubin (26.158.083) proposes, by analogy with other galaxies, that the rotation curve of the Galaxy is flat out to 60 kpc. Ardeberg and Mauri ce (1981) have studied radial velocHy data for young stars and tnterstellar gas from Ca II and H II lines along the border of the Carina arm. Pilowski (1981) has proposed a new basis for positional astronomy: an absolute stellar-geographical fundamental catalogue using geographical position determinations. II. Velocity Distribution Fujimoto (27.151.080) applied a theory of harmonic oscillation for a test star placed in a gravitational field of the Galaxy. He finds that the gravitational force due to CO clouds accelerate stars to a certain velocity dispersion. Nakamura (22.155.033) formulates a constraint on the velocity dispersion of the missing mass in the solar neighborhood. Chiu (28.111.019) has derived proper motions for stars from large telescope prime-focus plates. He developes a theory which leads to the suggestion that the Population I main sequence has a higher velocity dispersion than that of the solar neighborhood. The mean angular momentum of stars in the solar vicinity varies with age. Grosbol (26.155.031) has computed models for investigation of the variation assuming that this could be caused by a density wave potential. In an article by Larson (25.155.009) a discussion is given of the increase of velocity dispersion with age and an explanation is attempted. Menge de Freitas (28.111.005) computed velocity components for 726 nearby stars (data from Gliese's catalogue) along an axis parallel to the Cygnus arm and along another arm orthogonal to the first one. A discussion of averages and standard deviations is given. Peralta (25.155.006) studied the dispersion of velocity residuals for Population I stars and analyzed them as a function of galactic longitude and distance. Quiroga (27.155.010) compared results from stellar and interstellar medium studies and discussed the local galactic field of forces.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

Stone (21.112.006) studied kinematics for groups of 0 stars. He suggests that high velocity 0 stars are produced in massive close binary systems and presents a model for the evolution of such systems. A sample of high velocity OB stars were investigated by Carrasco et al. (28.155.044). The solar motion and mean peculiar velocities are found to be related to population groups. FOY (27.114.142) made a chemical analysis of 5 high velocity stars. Runaway stars have been studied by Isserstedt and Feitzinger (1981). They derived the distribution function for groups of runaway stars from the radial components of the peculiar velocities. Sion et al. (21.126.038) examined the kinematics of the variable and non-variable DA stars. Acker (28.135.017) derived relations between chemical, spatial and kinematic properties of planetary nebulae. Feast et al. (27.122.008) derived the velocity of the local standard of rest for Mira variables in a galactic centre window. The solar motion for 27 S stars has been derived from available radial velocities by Stephenson (22.112.001), who found no deviation in the result from the "basic" solar motion. Luyten (25.126.033) made an analysis for solar motion for faint white dwarfs. The galactic distribution of Cepheids is derived by Grayzeck (25.155.017) for a galactic longitude interval. Is is shown that H I and young stars share similar kinematics in this region of the Milky Way. A model for a "Centaurus Spur" feature is proposed. The velocity ellipsoid for RR Lyrae stars has been computed by Woolley (22.112.003) from radial velocities and from radial velocities combined with proper motions. Saio and Yoshii (26.155.016) derived kinematical quantities for 850 dwarf stars and RR Lyrae variables. A statistical study was performed. A metal indicator, transformed into ultraviolet excess, was defined and used in the statistics. Yoshii and Saio (26.155.008) used the same material for a discussion of the earliest history of the Galaxy. The kinematics and dynamics of the galactic globular cluster system was studied by Frenk and White (28.154.008). They compare models with observational data. Clube and Hatson (25.154.0)3) discuss the radial motion in the globular cluster system. In both cases conclusions about the galactic halo are drawn. REFERENCES Ardeberg, A., Maurice, E.: 1981, Astron. Astrophys. 98, 9. Isserstedt, J., Feitzinger, J.V.: 1981, Astron. Astrophys. 96, 181. Pilowski, K.: 1981, Veroff. Astr. Station Hannover 13. B. Interstellar Matter I. Large-Scale Motions From CO observations of molecular complexes related to H II regions Blitz (26.155.003) and Blitz et al. (28.155.027) determined the galactic rotation curve, the inner mass of the Galaxy and the velocity dispersions of the complexes. The observed north-south asymmetry of the rotation curve has been discussed by Jaakkola et al. (22.155.035), who present a model which tive an asymmetry in spatial distribution and in the kinemati.cs of neutral hydrogen.

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Gunn et al. (26.155.011) used published 21 cm H I observations for deriving the galactic rotation curve and values of Ro and 9 0 • The structure of Gould's Belt was investigated by Strauss et al. (25.131.020). They made a comparative study of optical and radioastronomical data. The possibility that Gould's Belt is either rotating or oscillating rigidly is discussed. Olano and Poeppel (1981) studied the kinematics of interstellar H I from an analysis of line profiles. The H I-shell of Gould's Belt was found to be strongly perturbed. From Ha scans maps of diffuse galactic Ha emission were constructed by Reynolds (27.155.002). The maps display the Ha intensity distribution for a series of radial velocity intervals between -76 and +8 km s-l. Contour diagrams derived from the Maryland-Green Bank galactic 2l-cm line survey are presented by Sato and Akabane (25.131.182). Radial velocities between -30 to +70 km s-l are covered. Chlewicki (28.155.040) presents the results of a study of the local arm structure from 2l-cm hydrogen line profiles. He uses the modelmaking method and finds a low value (1° - 5°) for the pitch angle of the local arm. Non-ci rcular motions in this arm are also discussed. Greisen and Lockman (25.155.025) studied the kinematics and distribution of cool H I clouds. The authors measured H I absorption profiles toward three galactic H II regions. Comparisons with synthetic spectra indicate that a nonlinear density wave model is to be preferred for this part of the Galaxy. The molecular clouds have been studied from various aspects. Bash (26.131.069) has presented a model for the orbits of such clouds in the Galaxy. The clouds are assumed to be launched from a spiral-shock wave and to orbit like particles with gravitational perturbations due to the density-wave potential. The model has been tested by comparing its results with observations. Liszt et al. (1981) point out that the presence of a residue of cold H I in galactic molecular clouds has several demonstrable effects on H I line profiles. These effects can influence the interpretation of the large-scale kinematics of the Galaxy from molecular observations. Fleck and Clark (1981) discuss a turbulent origin for the rotation of molecular clouds: the shearing action of different galactic rotation could maintain the turbulent flow. Liszt and Burton (26.131.079) give results in form of longitude-velocity diagrams from simulated "observations" of a three-dimensional distribution of model molecular clouds. The effects of kinematic perturbations associated with spiral structure are also discussed. A review of the observational evidence for high-velocity and high-temperature gas is given by t!cGray and Snow (26.l31.085). A description of the physical processes in the medium and a theoretical model are also given. Burton and Moore (25.155.012) give a discussion of a complex of forbidden veloctiy H I features in the anticenter region of the Galaxy. The location within the Galaxy of the cloud streams and their focus is demonstrated. Moore and Burton (26.155.055) have shown that the high-velocity H I clouds in the anticenter direction which is associated with a forbidden-velocity H I feature with negative value are correlated with a disturbance in the permitted-velocity gas. This disturbance is located within the Galaxy. Giovanelli (27.155.057) discusses the extended, continuous stream of neutral hydrogen flowing at high velocity in the galactic anticenter direction. Interpretations of the nature of the stream are presented.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

Knapp et al. (22.155.044) have searched for high-velocity 2l-cm emission from a possible extended galactic neutral hydrogen disk. The H I surface density is compared with corresponding data for other galaxies. A model is given; the agreement with observations is best for a value of the solar velocitye = 220 km s-l. Giovanelli (26.131.081) described his large scale, high sensitive survey in the 2l-cm line at NRAO. Hulsboch (26.131.080) gives a review of the observational properties of the high-velocity clouds. Talbot (27.155.001) used observed intensities of CO and H I emission from the Galaxy to compute surface densities of hydrogen. From the densities the rate of star formation per unit mass of gas is computed. This rate is proportional to Q - Qp ' A comparison with data obtained for M 83 is carried out. II. Central Region Lacy et al. (25.155.001) observed Ne II within the central parsec of the Galaxy. They found small sources of various velocities. From the cloud velocity distribution a value for the inner mass of the Galaxy is computed. Burton and Liszt (26.155.035, 28.155.048) present a model giving distribution and kinematics of H I gas within 1.5 kpc of the galactic center. Liszt and Burton (27.155.012) consider the gas distribution and kinematics within 2 kpc of the galactic nucleus and present a tilted-bar model (tilt 24°). Rohlfs and Schmidt-Y~ler (26.155.043) discuss the velocity field of the gas close to the galactic centre. Elliptical stream-lines have been proposed to explain the features along 340° < ~ < 22° which show expansion velocities. Another interpretation is given: the expansion field is considered as a description of a galactic wind. Bania (26.155.038, 28.155.042) has studied the latitude distribution of CO in the 3 kpc arm by surveying l2CO emission over a region in galactic longitude. The aim is to investigate whether the 3 kpc arm is a continuous ring, which has been doubted after earlier CO studies in the inner Galaxy. The l2CO emission survey shows that much of the dense molecular gas is found in large-scale features. These objects show large deviations from circular motions observed for molecular gas. A description of observations of molecular gas in absorption at large negative velocities is given by Linke at al. (1981). These millimeter-wave absorption features represent several molecules and can give evidence for a massive nuclear disk. Liszt.and Burton (26.131.079) have traced the kinematic patterns of molecular material in the inner Galaxy. A region around ~ = 0°, b = 0° is so far surveyed. REFERENCES Fleck, Linke, Liszt, Olano,

R.C. Jr., Clark, F.O.: 1981, Astrophys. J. 245, 898. R.A., Stark, A.A., Frerking, M.A.: 1981, Astrophys. J. 243, 147. H.S., Burton, W.B., Bania, T.M.: 1981, Astrophys. J. 246, 74. C.A., Poeppel, W.G.L.: 1981, Astron. Astrophys. 94, 151.

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6. DYNAMICS A. Stellar Orbits - Third Integral Although important studies have been carried out on stellar orbits in axisymmetric potentials, many papers consider now orbits in more complicated systems, e.g. in spiral or barred galaxies, or in systems with three degrees of freedom. Considerable attention has been given to resonant orbits or orbits near to resonances. I. Axisymmetric Galaxies and General Problems Kalnajs (26.151.082) gave a better epicyclic approximation for plane galactic orbits by perturbing the square of the radius instead of the radius itself. Agekyan and Saginashvilli (29.151.049) investigated the properties of nearly circular orbits in axisymmetric potentials. Baranov (26.151.062) studied periodic orbits in axisymmetric, nearly spherical systems. Allen and Moreno (21.151.098) computed orbits in a time-dependent axisymmetric galactic potential. Contopoulos (26.151.093) reviewed the integrable and stochastic behavior of stellar systems. Manabe (26.155.009) examined the applicability of approximate third integrals for stellar orbits in the Galaxy. Resonant systems, orbits at or near resonances have been studied by Andrle (26.151.032), Contopoulos and Zikides (28.042.033) and Contopoulos and Michaelidis (28.042.059). Michaelidis (28.151.056) discussed in detail the 2/3 resonance, Contopoulos (198la) the 4/1 resonance. Contopoulos (22.042.064) described a method for constructing integrable systems that have higher-order resonance. Other problems for systems with two degrees of freedom have been investigated by Magnenat (26.042.013) and Antonopoulos and Barbanis (26.151.028). Dynamical systems with three degrees of freedom have been studied by Contopoulos (25.042.l37), Contopoulos et al. (26.042.064), ~.artinet and Magnenat (29.151.039) and Martinet et al. (1981). Various algorithms for calculating orbits numerically have been compared by Papp et al. (22.151.056, 27.151.034) and by House et al. (22.042.086). II. Spiral Galaxies Orbits in spiral potentials in general: Frahm et al. (25.151.029) and Frahm and Thielheim (26.151.038) calculated individual stellar orbits in order to demonstrate the response to a spiral perturbation. Fuchs and Thielheim (26.151.037) and Frahm et al. (26.155.001) obtained periodic orbits in the epicyclic approximation and illustrated spiral density waves by the superposition of such orbits. Orbits at the inner Lindblad resonance have been calculated by Berry and de Smet (22.151.098, 22.151.099, 26.151.017). They find four subfamilies of stable, resonant orbits for an extensive inner Lindblad resonance region. Orbits at the corotation resonance: Colin (26.151.002) d~scussed the angular motion of trapped stars. Papayannopoulos (26.151.023, 26.151.060) studied numerically and theoretically the properties of orbits near corotation and their invariant curves. Palous (28.151.002) described non-linear effects near the particle resonance.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

III. Barred Galaxies Vandervoort (26.151.008) investigated isolating integrals of the motion for stellar orbits in a rotating galactic bar. He concludes that the orbits behave as if there is an additional isolating integral (besides the Jacobi integral) and that this behavior is represented well in terms of a constructed formal integral. Contopoulos and Papayannopoulos (28.151.083) studied orbits in weak and strong rotating bars, especially the main families of periodic orbits. Contopoulos (198lb) studied the effects of resonances near corotation in barred galaxies and concluded that most bars end at corotation. Schwarzschild (26.151.009), Heiligmann and Schwarzschild (26.151.055) and Goodman and Schwarzschild (1981) calculated numerically orbits in a non-rotating triaxial stellar system and found evidence for three effective integrals of motion. IV. Relaxation The diffusion of stellar orbits by a stochastic component of the galactic gravitational field has been studied by Fujimoto (27.151.080), Fuchs (1980) and Icke (1980). Large molecular clouds are probably most efficient in perturbing the regular orbits of stars. REFERENCES Contopoulos, G.: 1981a, Celestial Mech. 24, 355. Contopoulos, G.: 1981b, Astron. Astrophys. (in press) = ESO Preprint No. 159. Fuchs, B.: 1980, Dissertation Univ. Kiel. Goodman, J., Schwarzschild, M.: 1981, Astrophys. J. 245, 1087. Icke, V.: 1980, Bull. American Astron. Soc. 12, 818. Martinet, L., Magnenat, P., Verhulst, F.: 1981, Celestial Mech. (in press). B. Models of the Galaxy I. Initial Data for Galactic Mass Modelling Two observational trends affect galactic mass modelling: new data on the rotation curve and galactic constants. Recent determinations (26.155.003, 26.155.011, 26.113.021, 27.155.028, 28.155.027) have confirmed earlier conclusions (based mainly on the analogy with external galaxies) that the rotation curve of our Galaxy is essentially flat or even rising from R=12 to 16 kpc. These data suggest the presence of a massive corona. High infalling velocities of hydrogen clouds (Mirabel 198i) also suggest the presence of the massive corona. New data favour lower values of basic galactic constants, Ro=8.5 kpc and Vo=220 km s-l (26.155.011, 26.155.026, 26.155.067, 28.155.041). II. Mass Distribution Models Caldwell and Ostriker (1981) have published a detailed version of their mass distribution model. A detailed version of the Einasto model (26.155.041) is in preparation. A three-component model of the Galaxy consisting of a modified exponential disk, a spherical bulge and a massive corona has been suggeited by Rohlfs and Kreitschmann (19811. In this model Ra=8.5 kpc, Vo=225 km s- , Mbulge+disk=8.2xlO 0 Mo and Mcorona=5xlOllMo.

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De Vaucouleurs and Pence (22.155.031) presented a two-component model consisting of a spheroid with de Vaucouleurs density law and an exponential disk. This model attempts to represent photometric properties of the Galaxy. Another disk-spheroid model was constructed by Bahcall and Soneira (28.155.038) to calculate the expected distribution of faint stars in the galactic halo. The motion of globular clusters was used to estimate the mass of the Galaxy (21.155.013, 28.155.020). The result was 3-8xlO ll Mo . Gott and Thuan (21.158.236) and Einasto and Lynden-Bell (1981) calculated the orbit of K3l and Galaxy and deduced the total mass of these galaxies 4-8xl0 12 Mo • Detailed mass distribution models have been calculated for M3l (25.158.131, 25.151.007) and M8l (21.151.068, 27.158.315, 27.158.305, 28.151.007, 28.151.008) . III. Hydrodynamical Models Solving hydrodynamical equations of motion Bhattachryya and Basu (28.151.084) derived a flow model imitating closely the observed rotation velocity. Waxman (21.151.041) constructed a model which exhibits main features of dynamical interaction between the gaseous component of the galactic disk and the surrounding halo. Bregman (27.155.023) examined the interaction between the stellar bulge 'vind and di sk of gas. Stellar 'vinc ~JaS studied also by Bardeen and Berger (21.151.018). IV. Theoretical Models A closed system of six hydrodynamic equations was derived by Hunter (25.151.001) to study the dynamics of perturbed motion in thin disk galaxies. A set of closed moment equations was presented by Berman and Mark (25.151.084). Caimi and Dallaporta (22.151.080) presented a class of models consisting of two polytropic spheroids. Kutuzov and Osipkov (27.151.013) suggested a generalized model of the regular gravitational field of galaxies. Methods of mass modelling were studied by Agekyan and Saginashvili (21.151.009), Spaenhauer (21.151.021), Kutuzov and Sergeev (22.151.097), Peng et al. (22.151.086), Munier et al. (26.151.026), Schorr (26.151.029) and Xu (28.151.028). REFERENCES Caldwell, J.A.R., and Ostriker, J.P.: 1981 (in press). Einasto, J., and Lynden-Bell, D.: 1981, Mon. Not. R. astr. Soc. (in press). Mirabel, I.F.: 1981, Astron. Astrophys. (in press). C. Spiral Structure I. Reviews The spiral structure of galaxies is probably mainly due to density waves of some kind, primarily produced by gravitational forces. The stationarity of the lifetime, the maintenance and the origin of such density waves are under discussion. The density wave may be either supported by its own self-consistent field and caused by unstable global spiral modes or

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

instabilities, as considered in the conventional density-wave theory. Or the density wave may be mainly forced by other internal or external perturbations of the gravitational field, such as neighbouring galaxies, oval distortions or bars in the inner regions of galaxies, circulating density enhancements of various nature and origin. Reviews of the recent developments, theoretical problems and observational confrontations of gravitational theories of spiral structure have been given by Athanassou1a (26.151.090), Bertin (27.151.094), Contopou1os (22.151.043), Edmunds (27.151.005), Jones and Tremaine (25.151.014), Lin (22.151.070), Lin and Lau (26.151.061), Lin and Yuan (22.155.022), Mark (28.151.102), Schmidt-Kaler and Feitzinger (eds., 25.012.012), Toomre (1981) and Hie1en (25.151.076, 26.151.041). II. Spiral Modes, Origin and Maintenance of Spiral Structure The dispersion relation for density waves has been studied by Miller (22.151.050), Nishimoto (26.151.015) and Contopou1os (28.151.023). The response density and the behavior of the wave near the Lindblad resonances have been derived by Vandervoort (21.151.031), Contopou1os (25.151.003, 26.151.049) and Athanassou1a (26.151.050), near the corotation resonance by Mennessier and Martinet (25.151.102) and Morozov and Shukhman (27.151.056). Unstable spiral modes which can be responsible for the origin and maintenance of spiral density waves, have been investigated by Lau and Bertin (22.151.066), Pannatoni (1979), Panna toni and Lau (1979), Mark et a1. (26.151.044) and Lau and Haass (26.151.045). Astronomers in China have played an important role in the further development of the density-wave theory: Chin et a1. (27.151.087), Hu (26.151.091), Huang (25.151.098), Huang et a1. (26.151.039), Liu (26.151.064), Liu and Fang (25.151.012), Peng et a1. (26.151.021), Qin et a1. (26.151.065, 26.151.066), Song (27.151.040), Xu (26.151.020, 27.151.035, 27.151.036, 28.151.004, 28.151.071), Yue (26.151.019) and Yueh (15.151.088). Global spiral modes in stellar disks have been numerically investigated by Zang (26.151.070) for the case of a flat rotation curve and by Haass (28.151.062) for a disk with Kuzmin's density distribution. Aoki et a1. (26.151.103, 26.151.104) studied unstable global mo~es for gaseous disks with a density distribution according to Kuzmin-Toomre. lye et a1. (1981) investigated unstable global shearing modes for the same disk models. Various aspects of the structure, maintenance and excitation of density waves or other spiral perturbations have been investigated by Abramyan (25.151.026), Ambastha and Varma (21.151.095), Drury (28.151.054), Fridman (26.151.001), Fridman et a1. (29.151.003), Fujimoto and Tosa (28.151.076), Innanen and Papp (28.151.068, 28.151.117), Lapin and Raevskij (28.151.046), Morozov (25.151.078), Nishida et a1. (1981), Nuritdinov (25.151.027), Raevskij (27.151.083), Robe (25.151.070), \-laxman (27.151.011,27.151.012) and Woodward (28.151.017) • In recent years, much theoretical work has been devoted to studies of the driving of density waves by bars or oval distortions in galaxies: Athanassou1a (28.151.009), Berman et a1. (26.151.027), Korchagin and Sheve1ev (29.151.007), Lynden-Bell (25.151.030, 26.151.047, 29.151.071), Sorensen (29.151.124), Thie1heim (28.151.085, 28.151.118, 29.151.031) and Thie1heim and Wolff (28.151.039, 29.151.052). Most papers consider now also stellar disks and include the self-gravity of the driven spirals.

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Contopoulos (28.151.106) reviewed the stellar dynamics of barred galaxies and investigated problems of the extent (27.151.008) and self-consistency (1981) of bars. Toomre (1981) and Zang (28.151.061) investigated the origin of spiral structure by "swing amplification", i.e. the collective response of stellar orbits (including self-gravity) to tidal forces (e.g. caused by neighbouring galaxies). Goldreich and Tremaine (26.151.054) studied the excitation of density waves at the Lindblad and corotation resonances by an external potential. Mathematical tools for dealing with stellar dynamics of thin galactic disks, especially with respect to instabilities and waves in such systems, have been improved by Aoki and lye (22.151.044), Berman and Mark (25.151.084), Bertin and Mark (26.151.069), Hunter (25.151.001) and Ka1najs (26.151.082). Beside the density-wave theory and other gravitational explanations of spiral arms, there are various proposals for explaining the spiral structure of galaxies by other, non-gravitational mechanisms: Explosive origins of spiral arms have been studied by Havnes (22.151.052) and Schmidt-Kaler (26.151.043). Jaaniste (28.151.069) discussed an accretion theory of spiral structure by infa1ling gas. Piddington (22.151.081) advocates a hydromagnetic or magneto-tidel mechanism. Self-propagating stochastic star formation has been investigated by Gerola and Seiden (25.151.090), Seiden et a1. (26.151.012), Seiden and Gero1a (26.151.030), Comins (29.151.001) and Feitzinger et a1. (1981). III. Gas Flow and Shocks Roberts (28.151.111) reviewed the gas dynamics in ordinary and barred spirals. Levinson and Roberts (28.155.009, 29.151.058) developed a cloud/particle model for gas flow in galaxies and studied the spiral structure for a cloudy, supernovae-dominated interstellar medium. Reinhardt and Schmidt-Kaler (26.155.062) and Schmidt-Kaler and Wiegandt (28.131.084) investigated the implications of a very hot and complex interstellar medium for the propagation of density waves and shocks. Cowie (27.131.066, 1981) discussed the dynamics of agglomerating ensembles of clouds and the formation of molecular clouds by instabilities of spiral arms. Soukup and Yuan (27.155.017, 1981) studied the vertical extension of spiral shock fronts. Tubbs (28.151.026) determined the vertical gas structure of galactic shocks and discussed thermal phase effects and self-gravity of the gas. Nelson and Matsuda (27.151.021) investigated corrugation waves in the gas discs of spiral galaxies (including shocks) and the excitation of such gas oscillations in z by warps. Roberts (26.151.048) reviewed the gas response to bar-like distortions. Gaseous density waves and shocks in barred spirals have been studied by Roberts e1 al. (25.151.086, 26.151.031), Sanders and Tubbs (27.151.003) and van A1bada and Roberts (28.151.016). Huntley (25.151.087,27.158.322) investigated the self-gravitating gas flow in barred spiral galaxies. Schwarz (27.151.086, 1981) derived the gas response to a rotating stellar bar by following the orbits of particles which collide inelastically. Kato and lnagaki (22.151.018) examined the angular momentum transport and the change of gas distribution near corotation by a bar.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

IV. Observational Aspects Visser (28.151.007, 28.151.008) successfully explained the observed structure and kinematics of HI in M81 in terms of the density-wave theory including gas shocks. Kormendy and Norman (26.151.034) surveyed 54 galaxies with published rotation curves and concluded that global spiral patterns occur in differentially-rotating galaxies only in the presence of bars or companions. Feitzinger and Schmidt-Kaler (26.151.046, 28.151.005) calculated the energies and decay times of density waves for 25 galaxies of various types. Pence (1981) compared the observed velocity field in the barred spiral galaxy NGC 253 with the predictions for a linear density wave. The galactic distribution and kinematics of giant HII regions have been discussed by Lockmann (26.132.004), using linear density waves, and by Wie1en (26.151.041, 26.155.014), using non-linear gas motions including shocks. Other direct observational confrontations of the observed structure and kinematics of our Galaxy with the density-wave theory have been carried out by Suchkov (22.151.063), Pav10vskaya and Suchkov (22.155.057, 27.155.039), Mishurov et a1. (25.155.026), Grosbo1 (26.155.031), Joshi (27.155.033), Lindblad (28.155.016) and Terzides (1981). The drift and broadening of ageing spiral arms and their observational consequences for our Galaxy and other galaxies have been derived using density-wave-theory concepts, by Bash (26.131.069, 26.151.033), ~Jie1en (26.151.041), Fuchs (1980), Fuchs and Thie1heim (28.151.038), Yuan and Grosbo1 (29.151.021) and Bash and Visser (1981); see also Lynga (27.155.024). Feitzinger and Gisk (22.151.057) discussed the disruption of material arms by the tidal field of density waves. Innanen et a1. (22.155.032) studied the orbit of the sun in the presence of a density wave. Star formation in galaxies with regard to density-wave theory has been studied by Davies et a1. (21.151.096), Kaufman (26.151.013,26.155.006), Casse et a1. (26.155.012) and Talbot (27.155.001). REFERENCES Bash, F.N., Visser, H.C.D.: 1981, Astrophys. J. 247, 488. Contopoulos, G.: 1981, Astron. Astrophys. (in press) ESO Preprint No. 149. Cowie, L.L.: 1981, Astrophys. J. 245, 66. Feitzinger, J.V., G1assgo1d, A.E., Gero1a, H., Seiden, P.E.: 1981, Astron. Astrophys. 98, 371. Fuchs, B.: 1980, Dissertation Univ. Kie1. lye, M., Ueda, T., Noguchi, M., Aoki, S.: 1981, preprint. Nishida, M.T., Yoshizawa, M., \latanabe, Y., Inagaki, S., Kato, S.: 1981, Pub!. Astron. Soc. Japan 33 (in press). Pannatoni, R.F.: 1979, Ph.D. Thesis, Massachusetts Inst. of Technology. Pannatoni, R.F., Lau, Y.Y.: 1979, Proc. Nat1. Acad. Sci. USA, 76, 4. Pence, W.D.: 1981, Astrophys. J. 247, 473. Schwarz, M.P.: 1981, Astrophys. J. 247, 77. Soukup, J.E., Yuan, C.: 1981, Astrophys. J. 246, 376. Terzides, C.K.: 1981, Astron. Astrophys. 99, 144. Toomre, A.: 1981, in S.M. Fall and D. Lynden-Bell (eds.), Structure and Evolution of Normal Galaxies, Cambridge Univ. Press (i.n press).

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D. Stabi1i1ty and Evolution I. Spiral Nodes & Stability Aoki and lye (22.151.044) obtained a biorthonorma1 set of analytical solutions of the Poisson equation for disk galaxies. See also Hunter (27.151.078). Aoki et a1. (26.151.103, 28.151.104) studied unstable global modes for gaseous disks with Toomre's density distribution. lye et a!. (1981a) studied unstabel global shearing modes for the same disk models. lye et al. (28.151.295) and lye et al. (198lb) obtained Fourier spectra of observed spiral patterns of N5l and NGC4254. A fine explanation of the mechanism behind the growth patterns of the different modes is to be found in Toomre' s article describing work by him and Kalnajs. It is very interesting to see the bumps along the arms found in the modes of lye et al. explained as the places where a weak leading wave propagates back out to be turned around and made visible by the swing amplifier near corotation. Goldreich & Tremaine (26.151.054) have discussed the response of a gas disk to a rigidly rotating external potential and show the torques involved to be identical to the stellar case. Reflection and transmission coefficients for modes propagating in the region of the swing amplifier are calculated by Drury (28.151.054). Dispersion relations for open spiral waves are considered by Contopoulos (28.151.023) and Morozov (28.151.012). Berman & Mark find the Ostriker-Peebles criterion fails for galaxies with strong nuclear bulges (26.151.022) while Abramyan & Oganessian discuss the stability of a disk surrounded by a spheroidal system. Non-linear modes are considered by Polyachenko & Shukhman (26.151.073) and by Nuritdinov (27.151.073). Non-linear interactions between such spiral waves are discussed by Raevskij (27.151.083). Lebovitz has considered the slow evolution of gaseous bodies preserving circulations and Lynden-Bell & Katz have derived a new non-linear energy principle for the equilibrium and stability of all steady flows of barotropic fluid. II. Barred Galaxies The theory of barred galaxies has drawn much attention. Contopoulos (25.151.003, 25.151.097, 26.151.049, 27.151.008, 28.151.016) has continued his development of the theory of self-consistent bars and the periodic orbits in them. Lynden-Bell (25.151.030) suggested a mechanism for generating bars and has given a criterion for the mutual gravity of the populations of two elongated orbits to lead to their alignment. He also discussed the evolution of bars due to angular momentum loss. The latter has been studied in more detail in the computer simulation of Sellwood and James (25.151.035). Athanassoula (28.151.009) has constructed self-consistent models of the spiral structure driven by bars while Sellwood (28.151.037 and 28.151.040) has found bars grow naturally in computer models with "live" haloes. Nezhinskij (28.151.045) has suggested a binuclear origin of barred galaxies. Vandervoort (28.151.031) has constructed bars that are the stellar dynamical analogues of the uniformly rotating poly tropes with hard equations of state. Studies of gas flow in barred galaxies have been most encouraging: Berman, Pollard and Hockney (26.151.027), Roberts, Huntley and van Albada (26.151.031), Roberts (26.151.048), Saunders and ~ubbs (27.151.004), Huntley (28.151.114), and Sorenson (28.151.115). Many of these models show shock structures which appear to be related to the dust lanes and star formation regions seen in real galaxies. Some of the

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

calculations are still plagued by spurious problems such as grid-viscosity, so they cannot be carried on for long without most of the gas accumulating at the centre. Dissipative particle methods such as those developed by Schwarz (27.151.086) do not suffer this particular difficulty and can be carried on for many rotations, however, they need many particles to produce accurate short structures. Burton and Liszt (28.155.048) apply a bar-like model to observations of gas flow in the central regions of the Galaxy. Kormendy has reviewed the stellar structure of the components of barred galaxies. III. Warps of Galactic Disks The problem of explaining the persistence of these warps has again proved popular. Tubbs and Sanders (25.151.074) have avoided the wrapping up problem of having a spherical halo which provides most of the gravity. Petrou (27.151.072) suggests a rapid change in the flattening of the halo as another way to reduce differential precession. A re~urn to models based around simple precession is advocated by Pipunov (25.151.083). Bertin and Mark (28.151.013) consider that tidal interactions excite self-sustaining warps. There remains the heterodyne excitation mechanism of Binney and the possibility that galaxies might not be perfectly aligned with the axis of their haloes. If galaxies have masses of 1012Mo then tides are larger and the tidal stretch of the halo may have a significant gravitational effect on a smaller disk. REFERENCES lye, H., Ueda, T., Noguchi, M. and Aoki, S.: 1981a, pre print • lye, M., Okamura, S., Hamabe, M., Watanabe, M.: 1981b, preprint. Kormendy, J.: 1981, The Structure and Evolution of Normal Galaxies, pp. 85-110, Eds. S.M. Fall and D. Lynden-Bell (Cambridge University Press). Lebovitz, N.R.: 1981, Proc. R. Soc. Lond. A 375,249. Lynden-Bell, D. and Katz, J.: 1981, Proc. R. Soc. Lond. A 378, 179. Toomre, A.: 1981, The Structure and Evolution of Normal Galaxies, pp. 111-136, Eds. S.M. Fall and D. Lynden-Bell (Cambridge University Press). E. Computer Simulations Computer simulations are now widely used for studies of the dynamics and evolutions of galaxies and their groupings. Clustering of gqlaxies in an expanding universe has been studied extensively by N-body simulations (25.151.055, 26.160.042, 25.151.056, 27.151.032, 27.151.006, Miller 1981). All these simulations have been successful in reproducing the observed clustering properties of galaxies and they support the gravitational instability picture in which galaxies form first and the cluster follows via mutual gravitational interactions. Doroshkevich et al. (28.162.001) also demonstrated the formation of a large-scale structure of the universe by Vlasov simulations. Galaxies are exposed to mutual interactions and environmental influences, and it is especially true in a dense cluster of galaxies. These effects on the dynamics and evolution of the galaxies can be seen in Miller and Smith (27.151.001), White (26.151.081, 27.151.022), Farouki and Shapiro (28.151.080, 1981), Efstathiou and Jones (25.151.004). The collapse and accompanying rapid relaxation of stellar systems were investigated by N-body simulations, which would be realized at the galaxy formation (25.151.065, 25.151.013, Miller and Smith, 1981a, b).

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Bar-like structure is very common to rotating stellar systems. Formation and dynamical characteristics of bars were studied by Combes and Sanders (1981) and Miller and Smith (25.151.041). Stability of rotating disks against bar formation was examined by Berman and Mark (26.151.022) and Sellwood (28.151.037). N-body simulations was applied also to spiral structure by Sellwood and James (25.151.035). Niller and Smith (27.151.002) found that the rotation does not make the (axisymmetric) elliptical galaxy so flat as expected conventionally. Alternative to the N-body simulation, the V1asov simulation were applied to flat stellar systems by Fujiwara (1981), Watanabe (1981) and Nishida et a1. (1981) and it was found that a large-scale prominent bar such as noticed in the N-body simulation does not appear in the V1asov simulations. Various responses of gas to gravitational forcing like bar and other density-wave potentials were studied by several authors: Berman, Pollard and Hockney (26.151.027); Huntley (27.158.322); Roberts, Huntley and van A1bada (26.151.031); Sanders and Tubbs (27.151.003); Tubbs (28.151.026); Soukup and Yuan 1981; Visser (28.151.008); Levinson and Roberts 1981. Tubbs (28.158.207), Icke (25.151.051), Sanders (1981), Nelson and Matsuda (27.151.021) have conducted hydrodynamic simulations in order to understand some gasdynamica1 phenomena often observed in the Galaxy and ga1axi.es. The stochastic star formation was introduced by Seiden and Gero1a (26.151.030) as a non-dynamical formation mechanism of a large-scale structure in galaxies and it was applied to the Large Mage11anic Cloud by Feitzinger et a1. (1981). Murai and Fujimoto (28.159.018) conducted a numerical simulation of the ~1age11anic Clouds and the Galaxy with a massive halo of 7 x 1013Mo. and they have been successful in reproducing the geometry and the high-negative velocity of the Mage11anic Stream. REFERENCES Combes, F., and Sanders, R.H.: 1981, Astron. Astrophys. ~, 164. Farouki, R., and Shapiro, S.L.: 1981, Astrophys. J. 243, 32. Feitzinger, J.V., G1assgo1d, A.E., Gero1a, H., and Seiden, P.E.: 1981, Astron. Astrophys. 98, 371. Fujiwara, T.: 1981, Pub1. Astron. Soc. Japan 33, in press. Levinson, F .H., and Roberts, W.W.: 1981, Astrophys. J. 245, 465. Miller, R.H., and Smith, B.F.: 1981a, Astrophys. J. 244, 33. Miller, R.H., and Smith, B.F.: 1981b, Astrophys. J. 244, 467. Miller, R.H.: 1981, preprint. Nishida, M.T., Yoshizawa, M., Watanabe, Y., Inagaki, S., and Kato, S.: 1981, Pub1. Astron. Soc. Japan 33, in press. Sanders, R.H.: 1981, Astrophys.- J. 244, 820. Soukup, J.E., and Yuan, C.: 1981, Astrophys. J. 256, 376. Hatanabe, Y., Inagaki, S., Nishida, M.T., Tanaka-;Y., and Kato, S.: 1981, Pub1. Astron. Soc. Japan ~, in press.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

F. Magnetic Fields, X-Ray and y-Ray Sources I. Magnetic Fields A review paper by Verschuur (26.156.021) summarizes observations of the galactic magnetic field. Parker (26.003.103) published a book on cosmical magnetic fields in which chapters 1, 2,17,18,19 and 22 concern the galactic magnetic field. lJasserman (22.151.012) formulated NED galaxy formation and derived the present intergalactic magnetic field of < 10-9C• Muradyan (22.156.018) considered the possibility that the galactic magnetic fields 10-6C are relics of dipole field of Ambartsumyan's protogalactic matter. Jaffe (28.160.063) and Roland (1981) examined dynamo effect in the turbulent wake behind the rich cluster of galaxies to amplify the seed field 10-9G to 10-6C• De Young (28.141.103) indicated that the energy of extragalactic radio sources can be supplied by MHD turbulence. Bicknell and Henriksen (28.158.200) analysed beam dynamics including magnetic field to explain the radio jets emerging from active galaxies. Sturrock and Stern (27.155.043) showed that the MHD instability in the differentially rotating disk releases the excess magnetic energy out of the disk to heat the galactic corona to 106K. The large-scale magnetic fields in galaxies are estimated to be plane-parallel to the symmetry plane from the observational data on optical polarization for the spirals NGG 3623 and NGG 4216 (21.158.239) and from stellar polarization data for our Galaxy (21.156.016). The bisymmetric open spiral configuration of magnetic fields is found in M3l, M5l, and M8l from rotation measures (RMs) of polarized radiation at wavelength 21 cm (22.158.044, 28.158.174, Sofue and Takano 1981) and possibly in our Galaxy from RMs of extragalactic radio sources (28.156.011) and RMs of pulsars (27.156.009). Sawa and Fujimoto (28.151.075) presented a mechanism by which the bisymmetric configuration is stationary in the disk without being twisted by differential rotation. In the bisymmetric magnetic field a conducting gas condenses in spiral to excite and sustain the density waves (28.151.076). A magneto-tidal model explains the broad optical arms and corresponding HI arms observed in M5l-type spirals (22.151.081). From the analysis on spiral arm spurs on B and I photographs, Elmegreen (28.158.230) concluded that spurs may be formed by large-scale wave processes. Heiles et al. (28.155.045) indicated that the north polar spur has a shell structure as the result of spherical shock; the outer is HI shell with B < 6 x 10-6G and the inner the radio continuum shell with B > 1.2 x 10-6G• Based on the theoretical analysis Lerche and Milne (27.131.026) interpreted the fluctuations in extinction of planetary nebulae as the result of turbulent interstellar medium. A correlation length and a fluctuating angle for the irregular magnetic fields were estimated by Nee (27.131.141) following Langevin's scheme. From the derived criteria for Parker instability a system of interstellar gas and magnetic field is unstable to permanent agitation if it is in horizontal equilibrium configuration (27.062.109) and also if in curved periodic configuration (22.062.019). Brindle et al. (22.156.002) showed that the distribution of synchrotron radio in the Galaxy is explained by the model in which radio disk grows thin towards the galactic center. Higdon (26.156.004) derived a range of cosmic-ray intensities and magnetic field strengths in the Galaxy from the comparison of synchrotron and y-ray emissivities. The diffusion coefficient of cosmic-rays in turbulent magnetic field is derived which confines cosmic-rays in the disk region R ~ 5 - 6 kpc (25.156.002) and which exhibits the compound diffusion (25.143.034).

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II. Cosmic Rays Large-scale characteristics of interstellar gas and magnetic fields have been discussed over many years from the cosmic ray data obtained in the solar system. New results about the Galaxy were provided steadily in these three years: the existence of a galactic halo and the lifetime of the cosmic-ray nucleons and electrons are examined critically, for example, in relation to their confinement in the Galaxy (28.143.029). Cosmic-ray nucleons. The substantial amount of Li, Be and B in the cosmic-ray nucleon and the recent discovery of the radio isotope lOBe enabled us to know the behavior of energetic particles in our Galaxy. The total amount of interstellar matter traversed by cosmic rays and their escape-time from the Galaxy have been evaluated as 5 gr cm- 2 and 2 x 10 7 years, respectively. If the average density of interstellar matter is 1.7 x 10- 24 gr cm- 2 (1 H atom cm- 3 ), however, these two values are inconsistent, from which a variety of models for the Galaxy were introduced. The energetic particles spend most of their lifetime for random walk in the halo and only its fraction for interaction with interstellar gas in the flat disk. Among a number of papers which were published in the period of 1979 to 1981 for the confinement problems of the cosmic-ray nucleon, Ginzburg et al. (27.143.010) examined extensively the diffusion cosmic nuclei in the disk and static halo whose vertical thickness is respectively 100 pc and a few kpc. A dynamical (convective) state of the halo was introduced initially by reasoning that the halo gas and magnetic field cannot be in a static state but it is driven outward through self-generated hydromagnetic waves. Jones (25.143.030) and Freedman et al. (27.143.009) solved analytically a one-dimensional (perpendicular to the galactic plane) diffusion-convection equation for cosmic-ray nuclei and showed that the observed mean path length (gr cm- 2 ) versus nuclear energy (GeV/Nuc) can be interpreted if the outward convection velocity is 8 km s-l. (Note that these two papers are not all that were published about the halo problem. See references therein). More details about other isotope measurements and the corresponding propagation problems can be seen in papers presented at the 16th International Cosmic Ray Conference, Kyoto Japan (1979). Cosmic-ray antiprotons were discovered in the energy range of 200 MeV to 10 GeV, with the same power-law spectrum as the cosmic-ray proton but with the antiproton/proton ratio of 2 ~ 5 x 10- 4 (26.143.062, Bogomolov et al. 1979, Buffington et al. 1981). The data indicate that the cosmic-ray antiprotons were created by collisions of high-energy cosmic rays with interstellar fas and cosmic-ray protons have passed through substantially more than 5 gr cm- of material during their lifetime. Stochastic and energy-dependent processes in interstellar space have been suggested which act on the secondar antiproton after their creation. The upper-limited ratio He/He < 2 x 10- has been set.

S

Electrons. Measurements of cosmic-ray electrons have been continued to extend their energy spectrum up to 1013 eV. It is in a single power-law in the energy range 1 GeV to 10 3 GeV, with a slight steepening toward higher energies (25.143.004), 27.143.072 and references therein). To reproduce this energy spectrum theoretically, they employed the diffusion model and the en,rgy-dependent homogeneous leaky-box model, and obtained 1.0 (+2.0, -0.5) x 10 years as a galactic electron residence time, consistent with that estimated from the lOBe data.

STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

The electron spectrum is expected to show nonstatic fluctuation at energies above 1 TeV cue to the influence from a few nearby sources S since the lifetime with respect to energy loss at this energy is about 3 x 10 years for a total energy density of 1 eV cm- 3 of the interstellar space (25.143.019, 27.143.072). III. DHfuse Gamma Radiation in the Galaxy GaJactic gal".ma ray astronomy is now in exploratory phase, alreacy shifted from discovery phase of the early 1970's. The gamma radiation data are due mostly to the observations by the SAS-2, COS-B and balloon instruments. ~he present status of this research field is seen in Proc. COSPAR Symposium "Non-Solar Gamma Rays" edUed by Cowsik and Hills (28.012 .047) and in her review article by Cesarsky (28.143.029), in which are summadzerl the latest data about the energy spectrum and the intensity distribution confined to the thin galactic plane (28.157.012, 28.157.013, 28.157.014, 26.157.003). Through constructing galactic models for the gamma radiation and non thermal radio emission, two emission processes have been widely accepted to operate: (1) collisions of cosmic nucleus with interstellar matter producing nO meson which decays to y photons and (2) bremsstrahlung from cosmic ray electrons accelerated by interstellar nucleus. ~he bright y distribution at 50 0 < ~ < 310 0 suggests the enhanced fluxes of cosmic rays in the inner part of the Galaxy. The extended latitude distribution shows the presence of a diffuse halo above the disk, consistent with that derived from the model analyses of cosmic-ray nucleons and electrons. These large-scale characteristic of the Galaxy are, however, still qualitative anc1 not firmly establi.shed, because the distrfrution of interstellar matter is not known in the inner Galaxy and we cannot separate the fluxes of cosmic-ray electrons and magnetic fields in the region beyond the solar system (25.157.008, 26.156.004, 27.142.501, 28.157.012, 28.157.016, 27.156.001). REFERENCES Bogomolov, E.A., Lubyanaya, N.D., Pomanov, V.A., Stepanov, S.V., Shulakova, H.S.: J979, Proc. 16th Int. Cosmic Ray Conference, Kyoto 1,330. Buffington, A., Schindler, S.M., Pennypacker, C.R.: 1981, Astrophys. J. 248, (in preparation). RoJand, J.: 1981, Astron. Astrophys. 93, 407. Sofue, Y., Takano, T.: 1981, Publ. Astron. Soc. Japan~, 47. 7. GALACTIC ENVIRONMENT Absorption line measurements in the ultraviolet and visible have demonstrated the existence of a hot halo of 10 6 K gas along a number of sight lines through the halo. The strongest concentrations are found along low latitude lines of sight and these lines to the Mage11anic Clouds and to the Mage11anic Stream, (see Songaila, 1981, and Songai1a, Cowie and York, 1981). Dynamical modelling of the Magel1anic Stream with many different assumptions has become quite an industry. The paper by Murai and Fujimoto (28.159.018) is a very thorough work tracing back the motions of both Mage11anic Clouds in a heavy halo potential that gives V = 250 km/sec out to 200 kpc. Rather similar assumptions are used by Lin and Lynden-Bell who predict a measurable proper motion for the LMC of 2 mi11i-arc-seconds per year due East if the Galaxy has a heavy halo, and 1.5 if it does not. They have thus changed to "trailing stream" the sense of motion across the sky, advocated by Fujimoto and by Fei.tzinger, Schmidt-Kaler and Isserstedt. However, Tanaka using a Galaxy of much lower mass, has reproduced the stream

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quite well with a leading bridge model of the stream. It looks as though this controversy will only be finally settled when the proper motion has been measured. In the leading bridge models, the net proper motion will be much smaller than those quoted above. Fine structure in the northern extension of the Magellanic Stream has been mapped by Evers, PhHi.p and "'urner (27.159.028) and by Mirabel, Cohen and Davies (25.159.003). The velocity structure is considered by Hayes (26.159.003). Mirabel gives evidence for an interaction between the stream ane the Galaxy. Among the dwarf spheroidal satellites of the Galaxy, Carina and Ursa Minor have receive~ much attention. rarina's racial velocity is exceptionally large -450 ± 50 km/sec for an object so far away, Cannon et al. (1981). Ursa Mjnor has an l1.R. diagram w;th a blue hodzonta' branch which indicates great age and metal oef; ciency (Cudworth, SchoTImler and Olszenski). Lynden-Bell has pointed out that both Ursa Minor and Draco are oriente~ \vi th thei r major axi s accura tel y along the extension of the Magellanic Stream around the sky. For Ursa Hinor this indicates that i. t :i s being torn up by the Galaxy's tide as advocated by Hodge and Rickie. Its orbit is along the path of the Magellani.c Clouds from which it may have been torn in the very remote past. Draco's orientation may likewise have been determined from the orbital plane of the Hagellanic debris which formed jt. REFERENCES Cannon, R.D., Niss, B. and Norgaard-Nielsen, R.U.: 1981, Hon. Not. R. astr. Soc. 196, 1p. Lin, D.N.~and Lynden-Bell, D.: 1981, Han. Not. R. astr. Soc., (in press). Lynden-Bell, D.: 1982, Observatory, (in press). Songaila, A.: 1981, Astrophys. J. 248, 945. Songaila, A., Cowie, L.L. and York-;--i5.G.: 1981, Astrophys. J. 248, 956. Tanaka, K.I.: 1981, Publ. Astron. Soc. Japan~, 247.

G.G. Kuzmin Presjdent of the Commission

34. INTERSTELLAR MATTER AND PLANETARY NEBULAE (MATIERE INTERSTELLAIRE ET NEBULEUSES PLANETAIRES) PRESIDENT: V. Radhakrishnan VICE-PRESIDENT: M. Peimbert ORGANIZING COMMITTEE: T. de Jong, B.D. Donn, G.B. Field, L.A. Higgs, E.B. Kostyakova, J. Lequeux, U. Mebold, M. Morimoto, Y. Terzian, B. Zuckerman. 1. Introduction (V. Radhakrishnan) The subject of interstellar matter continues to be one of the most active fields of present day astronomical research. The advent of new instruments operating in the different parts of the electromagnetic spectrum has resulted in a phenomenal increase both in the amount of observational material, and in the theoretical work attempting to interpret or model the observations. This has made it increasingly difficult to cite all of the published work in the field, and to have room to report even in brief on the conclusions of these studies. The following sections of the report cover the period 1979-81. In fitting them together within the space allotted for this Commission's report, duplication of references has been avoided as far as possible. For the same reason, the names of several journals have been shortened to their well recognised (but not IAU recommended) abbreviations: The Astrophysical Journal (Ap.J.), Astronomy and Astrophysics (A&A), Astronomical Journal (A.J.), Monthly Notices of the Royal Astronomical Society (MNRAS) , Publications of the Astronomical Society of the Pacific (PASP), Bulletin of the American Astronomical Society (Bull. AAS), and the new Journal of Astrophysics and Astronomy (JAA). We list below the more important books, conference proceedings, surveys, and review articles concerning this Commission and published since 1979. MONOGRAPHS AND OTHER BOOKS Adams, D.J.: 1981, "Cosmic X-ray Astronomy", Heyden & Son Inc., London. Appenzeller, 1., Lequeux, J., Silk, J.: 1980, "Star Formation", 10th Advanced Course, Swiss Society of Astronomy and Astrophysics, Saas-Fee, Geneva Observatory. Dyson, J.E., Williams, D.A.: 1980, "The Physics of the Interstellar Medium", Manchester University Press. Dolginov, A.Z., Gnedin, Yu. N., Silant'ev, N.A.: 1979, "Propagation and Polarization of Radiation through Cosmic Medium", Nauka, Moscow. (In Russian) Kaplan, S.A., Pikel'ner, S.B.: 1979, "Physics of the Interstellar Medium", ed. N.G. Bochkarev, Nauka, Moscow. (In Russian) Kislyakov, A.G. (ed.): 1979, "Spectral Investigations of Cosmical and Atmospheric Radiation", IPF, Gorkij. Martin, P.G.: 1978, "Cosmic Dust: its impact on astronomy", Clarendon Press, Oxford. Martinov, D. Ya. (ed.): 1981, "Stars and Stellar Systems", Nauka, Moscow. (In Russian) Spitzer, L. Jr.: 1978, "Physical Processes in the Interstellar Medium", WileyInterscience. van Woerden, H., Brouw, W.N., van de Hulst, H.C. (eds.): 1980, "Oort and the Universe", D. Reidel Publishing Co. van de Hulst, H.C.: 1980, "Multiple Light Scattering", (Vols. 1 & 2), Academic Press, Inc. 413

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SYMPOSIUM REPORTS, CONFERENCE PROCEEDINGS, ETC. Andrew, B.H. (ed.): 1980, "Interstellar Molecules" (IAU Symp. 87), D. Reidel Publishing Co. Bernacca, P.L., Ruffini, R. (eds.): 1980, "Astrophysics from Spacelab" (Astrophysics and Space Science Library, Vol. 81), D. Reidel Publishing Co. Chapman, R.D. (ed.): 1981, "The Universe at Ultraviolet Wavelengths" (The First Two years of IUE), NASA Conference Publication 2171 (NASA CP-2171). Chiosi, C., Stalio, R. (eds.): 1981, "Effects of Mass-loss on Stellar Evolution" (IAU Colloq. 59, September 1980), Trieste Astronomical Observatory. "Elements et leurs isotopes dans I' univers, Les": 1979, Liege JUCIle Colloque International d'Astrophysique, Universite de Liege, Institut d'Astrophysique. Halliday, I., McIntosh, B.A. (eds.): 1980, "Solid Particles in the Solar System" (IAU Symp. 90), D. Reidel Publishing Co. Iben, 1. Jr., Renzini, A. (eds.): 1981, "Physical Processes in Red Giants" (Astrophysics and Space Science Library, Vol. 88), D. Reidel Publishing Co. "Protostars and Planets": IAU Colloq. 52 (Tucson, Arizona), The Moon and the Planets, 1979, 19, 107-315 and 1979, 20, 3-101, D. Reidel Publishing Co. Roger, D.S., Dewdney, P.E. (eds.): 1981,----"Regions of Recent Star Formation" (Penticton Workshop, June 1981), D. Reidel Publishing Co. Schuerman, D.W. (ed.): 1980, "Light Scattering by Irregularly Shaped Particles", Plenum Press. Setti, G., Fazio, G.G. (eds.): 1978, "Infrared Astronomy" (NATO Advanced Study Institute, July 1977), D. Reidel Publishing Co. Shaver, P.A. (ed.): 1980, "Radio Recombination Lines" (Astrophysics and Space Science Library, Vol. 80), D. Reidel Publishing Co. Solomon, P.M., Edmunds, M.G. (eds.): 1980, "Giant Molecular Clouds in the Galaxy" (Third Gregynog Astrophysics Workshop), Pergamon Press. "Spectres des Molecules Simples au Laboratoire et en Astrophysique, Les": 1980, Liege XXl e Colloque International d'Astrophysique, Universite de Liege. "Thermodynamics and Kinetics of Dust Formation in the Space Medium": 1979, Astrophysics and Space Science, Vol. ~, D. Reidel Publishing Co. Willis, A.J. (ed.): 1979, "The First Year of IDE", NASA ESA SRC, University College London. Wynn-Williams, C.G., Cruikshank, D.P. (eds.): 1981, "Infrared Astronomy" (IAU Symp. 96), D. Reidel Publishing Co. CATALOGUES, SURVEYS, ETC. Alloin, D., Collin-Souffrin, S., Joly, M.: 1979, "A Line-Intensity data compilation for a Sample of H I I Regions", A&A Suppl., ]2, 361. Avedisova, V.S.: 1981, "Catalogue of Star Formation Regions, Part I", Sci. Inf. of Astron. Council of Acad. Sci. USSR. Dixon, R., Sonneborn, G.: 1980, "A Master List of Nonstellar Optical Astronomical Objects", Ohio State University Press. Parker, R.A.R., Gull, T.R., Kirshner, R.P.: 1979, "An Emission-line Survey of the Milky Way", NASA Special Publication 434. Rossano, G., Craine, E.: 1980, "Near Infrared Photographic Sky Survey: a field index", Pachart Publishers. REVIEW ARTICLES Beckman, J.E., Moorwood, A.F.M.: 1979, "Infrared Astronomy", Rep. Prog. Phys., ~, 87. Cesarsky, C.J.: 1980, "Cosmic-Ray Confinement in the Galaxy", Annu. Rev. Astron. Astrophys., 18, 289. Felli, M.: 1979-;-"Properties of H II Regions" in Westerlund, B.E.(ed.), "Stars and Star Systems", D. Reidel Publishing Co., p. 195. Goudis, C.: 1979, "A Classification of the Available Astrophysical Data of Particular H II Regions", Astrophys. Space Sci., g, 417.

INTERSTELLAR MATTER AND PLANETARY NEBULAE

415

Habing, H.J., Israel, F.P.: 1979, "Compact H II Regions and OB Star Formation", Annu. Rev. Astron. Astrophys., ll, 345. McCray, R., Snow, T.P. Jr.: 1979, "The Violent Interstellar Medium",Annu. Rev. Astron. Astrophys., 17, 213. McKee, C.F.,"Hollenbach-:-D.J.: 1980, "Interstellar Shock Waves", Annu. Rev. Astron. Astrophys., 18, 219. Osterbrock, D.E-:-: 1980, "Physical Characteristics of Ionized Gaseous Nebulae", IAU ColI. 54, 99. Savage, B.D., Mathis, J.S.: 1979, "Observed Properties of Interstellar Dust". Annu. Rev. Astron. Astrophys., 17, 73. Seaton, M.J.: 1980, "Spectra of Ga~ous Nebulae", Quart. J. Roy. Astron. Soc., 21, 229. Terzian, Y.: 1980, "Planetary Nebulae", Quart. J. Roy. Astron. Soc., 21, 82. Verschuur, G.L.: 1979, "Observations of the Galactic Magnetic Field",Fundam. Cosmic Phys., 5, 113. Walsh, J .R.; 1980-;- "A Classification of the Available Astrophysical Data of Particular H II Regions - IX NGC 2264", Astrophys. Space Sci., ~, 227. Wannier, P.G.: 1980, "Nuclear Abundances and the Evolution of the Interstellar Medium", Annu. Rev. Astron. Astrophys., 18, 399. Whittet, D.C.B.: 1981, "The Composition of Interstellar Grains", Quart. J. Roy. Astron. Soc., 22, 3. Zuckerman, B.: 1980, "Envelopes Around Late-type Giant Stars", Annu. Rev. Astron. Astrophys., ~, 263. 2. Physical State and Dynamical Processes (J. Lequeux) This review covers the literature from January 1979 to mid-1981, but does not pretend to be complete. Emphasis has been put on theoretical work, but some observational work is also cited. Overlaps with other sections are unavoidable. Amongst topics not, or very incompletely, covered here, I list atomic and molecular processes, interstellar chemistry, dust formation and destruction, acceleration of cosmic rays and their interaction with interstellar matter, and topics related to galactic structure. The past three years of research have been dominated by the ever growing evidence that the interstellar medium (ISM) is in a state of buoyancy; in most situations only non-stationary models have a chance to give a possible representation of this medium. Emphasis has been put on the hydrodynamics of the various components and on their mutual interactions, in particular the role of shock waves due to supernovae, stellar winds and H II regions. Global models of the evolution of the ISM including mass exchange between the various components are starting to emerge. Models for the evolution of molecular clouds leading to star formation have been considerably refined and now include 3D hydrodynamical calculations. The reader should also look at the list of general references and review papers, some of which cover the present topics. A. DIFFUSE CLOUDS (DCs) General statistical studies have been published based either on 21-cm data (Crovisier, 1981, A&A, 94, 162; Dickey et al. 1979, Ap.J., 228, 465; Dickey et al. 1981, A&A, 101, 332) or~n optical data (Knude, 1981, A&A, 9~380). It appears that, although generally of smooth structure (Dickey, 1979-;--Ap.J., 233, 558), DCs contain denser regions with smaller velocity dispersions revealed by-IDolecular-line studies (Dickey et al. 1981, A&A, 98, 271 ; Kazes and Crovisier, A&A, 101, 401). The hotter gas (the old "intercloudmedium") appears to be pervasive but it is still not completely clear whether it only makes cloud envelopes or small clouds as predicted by the 3-component model of the ISM (Knude, 1979, A&A, 1l, 198; Heiles,

416

COMMISSION 34

1980, Ap.J., 235, 833). There is increasing evidence for the presence of shocks inside DCs (Jenkins and Shaya, 1979, Ap.J., 231, 55) and the depletion in heavy elements is smaller or absent if strong motions are present (e.g. York and Kinahan, 1979, Ap.J., 228, 127; Chaffee and Dunham, 1979, Ap.J., 233, 568; Shull, 1980, Ap.J., 238, 560), presumably due to grain sputtering (Trivedi and Larimer, 1981, Ap.J., 248, 563). There have been relatively few studies of the physical conditions in DCs (Pottasch et al. 1979, A&A, 74, L15; Roberge et al. 1981, Ap.J., 243, 817; Shchekinov, 1979, Astron. Zh., 56, 809; Arshutkin and Kolesnik, 1980, Astrofiz., 16, 737; Arshutkin, 1980, Astrometr. Astrofiz., 41, 29). The fractionation of deuterium has been studied by Bruston et al. (198~ Ap.J., 243, 161). DC stability has been discussed by Hartquist et al. (1979, A&A, 75, 137)~lannery and Press (1979, Ap.J., 231, 688) and McMillan et al. (1980, Ap.J., 240, 488); the latter predict large internal fluctuations of temperature and pressure. Rosner and Hartquist (1979, Ap.J. Lett., 231, L83) show that rotating magnetized DCs can develop hot "coronae ll •

B. HOT INTERSTELLAR MEDIUM The structure and origin of this component are still far from clear. A wide range of temperatures corresponding to various stages of ionization of 0, C and Si is present. Soft X-ray observations are sensitive to bremsstrahlung and line emission from widely distributed gas with T > 10 6K (Inoue et al. 1979, Ap.J.Lett., 227, L85; Fried et al. 1981, Ap.J., 242, 987; Schnopper et al. 1981, Ap.J., in press). For calculations of this emissio;-;ee Shull (1981, Ap.J.Suppl., ~,27); this gas is usually believed to come from more or less merged supernova remnants and stellar winds (e.g. Chevalier and Oegerle, 1979, Ap.J., 227, 398; Higdon and Lingenfelter, 1980, Ap.J., 239, 867) and to occupy most ~the IS volume (Dwek and Scalo, 1979, Ap.J. Lett., 233, L81). It is not clear whether the 0 VI absorption lines originate in this medium or mainly in cloud interfaces (Cowie et al., 1979, Ap.J., 232, 467). N V is less ubiquitous than 0 VI; when it is detected, the N VIO VI ratio suggests T ~ 2-3 10 5K (Smith and Hartquist, 1980, MNRAS, 192, 73P; Morton and Bhavsar, 1979, Ap.J., 228, 147), but do N V and 0 VI coexist? Extreme UV observations, however, seem to point to the actual existence of temperatures in this range, maybe in cloud interfaces (Stern and Bowyer, 1979, Ap.J., 230, 755). The C IV and Si IV lines appear to originate mainly in H II regions surrounding the observed hot stars (Smith et al. 1980, MNRAS, 191, 339; Black et al. 1980, Ap.J., 239, 502; Cowie et al. 1981, Ap.J., 248, 528) although some probably come from either a "semitorrid gas" (Bruhweiler7t al. 1979, Ap.J. Lett., 229, L39; 1980, Ap.J., 237, 19) or expanding shells (Cowie et al. op. cit.). This point has an obvious bearing on the still uncertain nature of the hot halo seen in these lines around our Galaxy (Savage and de Boer, 1979, Ap.J. Lett., 230, L77; Hartquist and Tallant, 1981, MNRAS, 196, 527) and perhaps around the Magellanic Clouds (de Boer and Savage, 1980, Ap.J~238, 86; Savage and de Boer, 1981, Ap.J., 243, 460; see, however, Prevot et al. 1980, A&A, 90, L13). Instabilities in the ho~SM have been suggested to be responsible for interstellar scintillation (Hall, 1980, MNRAS, 190, 353; 1981, MNRAS, 195, 685; see also Chashej and Shishov, 1980, Pis'ma Astron. Zh.,6, 574 and Pynzar-and Shishov, 1980, Astron. Zh., 57, 1187). Ionization conditions under X-ray heating have been studied by Bochkarev (1980, Pis'ma Astron. Zh., i, 289) and Beigman et al. (1981, preprint). C. MOLECULAR CLOUDS (MCs) Observations of MCs and their chemistry are reviewed elsewhere. I only want to point out that it is very difficult to obtain from comparisons of molecular line observations with models entirely convincing pictures of the physical conditions and dynamics of these clouds (see e.g. Stenholm, 1980, A&A, 92, 142 and references therein). However, some MCs at least appear definitely clumpy (e.g. Bastien et al. 1981, A&A, 98, L4). Statistics on MCs have been discussed e.g. by Stark (1979, Ph.D. Thesis,:Princeton) and Rowan-Robinson (1979, Ap.J., 234, Ill). Radiation transfer and heating of dust in MCs have been discussed by Rowan-Robinson (1980, Ap.J. Suppl. 44, 403), Brand (1979, A&A, 21, 47), Rouan (1979, A&A, ~, 102

INTERSTELLAR MATTER AND PLANETARY NEBULAE

417

and 1980, A&A, 87,169), Natta et al. (1981, A&A, 99, 289), Flannery et al. (1980, Ap.J., 236, 598>: Keene et al. (1980, Ap.J.Lett., 240, L43), Keene (1981, Ap.J., 245, 115). The gas temperature is never smaller than ~ 5K (Zuckerman and Kuiper, 1980, Ap.J., 235, 840; Evans et al. 1980, Ap.J., 239, 839) and it appears that even in hot regions gas can be heated by molecule collisions with dust grains (Phillips et al. 1981, Ap.J., 245, 512). The 21-cm line has been seen in self-absorption in MCs by many authors;~he interpretation of these observations is not easy (Levinson and Brown, 1980, Ap.J., 242, 416). It is not clear whether the corresponding H I only forms envelopes or is more distributed (see e.g. Bowers et al. 1980, Ap.J., 241, 183; Sherwood and Wilson, 1981, A&A, 101, 72). Ionization and its consequences have been studied by Wootten et al (1979, Ap.J., 234, 876), Elmegreen (1981, Ap.J., 232, 729), Guelin et al. (1981, A&A, in press); the ionization fraction is 10-7 to 10-8 . Vrba et al. (1981, Ap.J., 243, 489) and Goldreich and Kylafis (1981, Ap.J. Lett., 243, L75) deal with the magnetic field. Thermal-chemical models are built by Vial a et al (1979, A&A, 73, 174) and steady-state global models by de Jong et al. (1980, A&A, 91, 68). Fleck (1980, Ap.J., 242, 1019; 1981, Ap.J.Lett., 246, L151) has studied MCs stabilized by turbulence, while Norman and Silk (1980, Ap.J., 238, 158) propose a self-consistent model where MCs are stabilized by winds from T Tauri stars continuously formed inside. D. THE ROLE OF SHOCK AND IONIZATION FRONTS An enormous body of relevant observations has been recently accumulated; there is now ample evidence that the ISM is full of loops, shells, super-shells and patches, and high velocity gas associated with such phenomena. The following papers deal with the physics of these shocks and the corresponding radiation: Raymond (1979, Ap.J.Suppl., 39, 1), Hollenbach and McKee (1979, Ap.J., 41, 555), Canto and Dyson (1979, A&A, 76-;-318), Shull and McKee (1979, Ap.J., 227, 131), Draine (1980, Ap.J., 241, 1021) ,-Cowie et al. (1981, Ap.J., 247, 908), Zentsova and Urpin (1980, Astrofi~ 16, 553). Several papers deal with the effects of stellar winds and supernovae inside MCs, with emphasis on their possible detection: Shull (1980, Ap.J., 237, 769 and 238, 860), Wheeler et al. (1980, Ap.J., 237, 781), Wright (1980, Ap.J. Lett., 242, L2~ Draine (1981, Ap.J., 245, 880). Bubbles and superbubbles require an energy of the order of 1053 ergs or more if they expand in an averagedensity ISM (e.g. Heiles, 1979, Ap.J., 229, 533) requiring winds from hundreds of OB stars or many supernova explosions. If the medium is of very low density, one or a few events may suffice (Davelaar et al. 1980, A&A, 92, 231 and 97, 413; Higdon, 1981, Ap.J., 244, 88). These conditions can be met~n OB associations (Tomisaka et al. 1981, Astrophys. Space Sci., 78, 273; Bruhweiler et al. 1980, Ap.J.Lett., 238, L27). The energy problem for the-;upergiant holes seen in H I pictures of external galaxies is even worse; Tenorio-Tagle (1980, A&A, 88, 61; 1981, A&A, 94, 338) has suggested that they are due to collisions of high-velocity clouds with the gas disk (see also Holder, 1980, MNRAS, 191, 417). There is consensus that Herbig-Haro objects and bipolar nebulae are~rmed by stellar winds emitted by very young stars, possibly collimated (Canto, 1980, A&A, ~, 327; Hippelein and Munch, 1981, A&A, ~, 248; Schwartz and Dopita, 1980, Ap.J., 236, 543; Canto and Rodriguez, 1980, Ap.J., 239,982; Schwartz, 1981, Ap.J., 243,197; Canto et al., 1981, Ap.J., 244,102; Icke, 1981, Ap.J., 247, 152). The complex phenomena observed around IR~and KL in the Orion rIC and in W51, including the fast-moving H20 masers (Genzel et al. 1979, A&A, 78, 239; Downes et al. 1981, Ap.J., 244, 869; Genzel et al. 1981, Ap.J., 244, 884 and 247, 1039) are usually interpreted~ the effect of a stellar wind (Norman and Silk:-T979, Ap.J., 228, 197; Solomon et al. 1981, Ap.J. Lett., 245, LI9). Instabilities of ionization shock fronts have been shown to lead to the formation of elephant trunks, globules and may even trigger star formation (Giuliani, 1979, Ap.J., 233, 280 and 1980, Ap.J., 242, 219; Schneps et al. 1980, Ap.J., 240, 84; Brand, 1981, MNRAS, 197, 217; Welter and Schmid-Burgk, 1981, Ap.J., 245~27; Shchekinov, 1979, Astrofiz. 15, 347). The interaction between stellar winds and the ISM has been studied by Kahn-C1980, A&A, 83, 303) and Dopita (1981, Ap.J., 246, 65). Star formation following gas accretion by-; MC has been studied by Icke (1979, A&A, ~,352). The interaction of bubbles to form tunnels has been modelled by Jones et

418

COMMISSION 34

al. (1979, Ap.J., 232, 129) and the mechanical heating of the ISM by supernova remnants by Cox (1979, Ap.J., 234, 863 and 1981, Ap.J., 245, 534). E. EVOLUTION OF THE ISM We are still far from possessing a complete, self-consistent theory of the ISM. However, partial aspects have been studied in detail. The formation of H II regions on the side of MCs (the "champagne" or "blister" model) is described in a series of papers by Tenorio-Tagle and collaborators (see 1981, A&A, 99, 305 and references therein) and by Icke and collaborators (1979, Ap.J., 234,615; 1980, Ap.J., 236, 808; 1981, Ap.J.Suppl., 45, 585). The hydrodynamics~ cloud collisions which leads to partial coalescence and partial disruption has been studied by Smith (1980, Ap.J., 238, 842), Hausman (1981, Ap.J., 245, 72), Handbury et al. (1979, A&A, 77, 152) and Chieze and Lazareff (1980, A&A,-gy, 290); the latter have calculated~he equilibrium mass spectrum of the diffuse clouds (see also Kwan, 1979, Ap.J., 229, 567 and Cowie, 1980, Ap.J., 236, 868 and 1981, Ap.J., 245, 66). Whether the giant MCs are formed by coalescence (see e.g. Scoville and Hersh, 1979, Ap.J., 229, 578) is disputed. An alternative possibility is the collapse and fragmentation of large H I complexes formed in spiral arms (Blitz and Shu, 1980, Ap.J., 238, 148; Elmegreen, 1979, Ap.J., 231, 372; Polyachenko et al. 1980, Astron. Zh., iI, 497 and Morozov, 1981, Pis'ma Astron. Zh., 7, 9) possibly helped by the Parker instability (Elmegreen, 1981, preprints). Some-authors have proposed that turbulence possibly generated by galactic differential rotation determines the rotation and the fate of IS clouds (Larson, 1979, MNRAS,186, 479 and 1981, MNRAS, 194, 809; Fleck and Clark, 1981, Ap.J., 245,898). The damping of the motion of MCs in the Galaxy has been studied by Elmegreen (1981, Ap.J., 243, 512) and Surd in (1980, Astr. Circ. URSS No. 1113) and shown to be efficient. Disruption of MCs by HII regions has been studied in the framework of the blister model (see above, and Whitworth, 1979, MNRAS, 186, 59; Mazurek, 1980, A&A, 90, 65), and the propagation of star formation in a cloud complex has been discusse~by Bedijn and Tenorio-Tagle (1980, A&A, 88, 58). A dynamical model for formation of neutral clouds in the halo (the "galactic fountain") has been studied by Bregman (1980, Ap.J., 236, 577) and Cox (1981, Ap.J., 245, 534). Semi-empirical global models of massive cloud evolution and star formation in the Galaxy have been built by Bania and Lyon (1980, Ap.J., 239, 173), Bash et al. (1981, Ap.J., 245, 92), Levinson and Roberts (1981, Ap.J., 245~65) and Huntley and Gerola (1981, Ap.J. Lett., 248, L69). -3. Neutral Atomic Hydrogen (H I) (U. Mebold) Since photographic presentations of the H I distribution over nearly the entire sky have become available, the main emphasis now in 21-cm line research is on investigations of filamentary structures and their relations to radio- optical- or X-ray features like supernova remnants (SNR), H II regions, stellar associations etc. New 21-cm line surveys have led to complete sky coverage: Kerr et al. (1981, A&A Suppl., 44, 63) present a 21-cm line longitude-velocity map of the galactic equator for 231 0 ~ ~ ~ 350 0 and latitude-velocity maps for Ibl < 40 and 263 0 < ~ - uv sp. Gustatfason & Ardeberg (22.113.027)- comparison of theory to R~B st. HartwiCK & McClure (27.113.001)- rG st. CN-indices via COO photo Hesser (22.114.004)- CN var. in 80 st. br. than B= +16.2 Hesser & Bel I (27.114.201)- CN-abuna. var. frorr sp. of 7 upper MS st. Keith & tlutler (27.154.005)- memb. and rnetallicity of 3 RR Lyr st. Mall ia (22.154.021)- sp. of AGB st. Norris E. Cottrell (250154.012)- CN-str. of 2 AGB st. Norris & Freeman (250154.0211- CN distrib. froll' 142 rG st. sp._ Pilachowski et al. (27.154.001)- c.c. compo to old disk cl. NGC 2420 Smith, H.A. (25.154.0071- acund. grad. in cl. welcn & Cooe (27.154.018)- DAD energy distrib. C0050-268 (NGC 288) Alcaino & w. Liller (28.154.043)- CMD to MS :iamus' & ~nugarov (25.1:)4.030)- faint st. photo Welch & Code (27.154.01d)- DAO energy distrib. COIOO-711 (NGC 36L) welch & Code (270154.018)- DAD energy aistrib. C0310-554 (NGC 1261) Alcaino (26.154.008)- CMD welch & ~ode (27.154.018)- OAO energy distrib. C0325+794 (Pal 11 Cowley et al. (L1.114.010)- sp. of rG st. C0354-498 (AM 1) Madore & Arp (25.154.005)- discovery C0422-213 (Er I 11 west & Bartaya (26.154.009)- sp. and integr. UBV p.e. photo C0443+313 (Pa I 2) Cowley et al. (21.114.010)- sp. of rG st. Harris (27.154.002)- dist. and structural properties

STAR CLUSTERS AND ASSOCIATIONS

511

(NGC 1851) 30wers et al. (io.l,4.015)- 21-cm. ana 1612 MHz ODS. for gas content Jupree et al. (2:>.154.017)- uv sp. lAG Circ. 3209 and 3226 (21.154.032)- detection of neutral H Jernigan & Clark (2b.154.002)- location at X-ray source Snawl & R.E.Whlte (28.154.004)- eq. coora. of cl. center to ± 1" Smith, H.A. (27.154.065)- chem. abund. gradient Strauss (22.1'4.01ll- multi-color strip photo welch & Code (27.154.018)- OAO energy aistrib.

CO~12-400

(NGC 1904, M 79) Strauss (22.15".011)- multi-color strip photo Troiano et al. (21.1,4.004)- unsuccesful search for CO welcn & Cooe (27.154.018)- DAD energy aistrib.

CO~2Z-24:>

C0647-3!:19 (NGC 2298) van Aloada et al. (25.1,4.020)- ANS far-uv photo C0734+390 (NGC 2419) Canterna & Schommer (21.154.005)- chem. abund. Troiano et al. (21.154.004)- unsuccesful search for CO C0737-337 (AM 2) Madore & Arp (25.154.005)- discovery (;0911-646 (NGC 28(6) Harris (21.154.021)- p.e. UBV and DOD phct. Strauss (22.154.011)- multi-color strip photo C0921-770 (E 3) van den I:lergh et al. (28.154.002)- st.-poor cl. CI003+003 (Pal 3) Canterna & Schommer (21.154.005)- chem. abuno. Cowley et al. (21.114.010)- sp. of rG st. C1126+292 (Pal 4) Canterna & SChommer (21.154.005)- che~. abuna. Cowley et al. (21.114.010)- sp. of rG st. C1310+1b4 (N;C 5024, M 53) DiCkey & Melkan (27.154.016)- search for oH-em. Gopal-Krishna & Steppe (28.141.024)- radio continuum obs. at 2.7, 4.8, and 10.7 GHz Rood (R.) et al. (22.141.092)- 1400 MHz radio sources van Alcada et al. (25.154.020)- ANS far-lJv photo C1313+179 (NGC 5053) Canterna & Schommer (21.154.005)- chern. abund. Dickey & ~alkan (27.154.016)- search for oH-em.

512

COMMISSION 37

C132.-.\-472 (NGC 5139, fA) Cen) joehm-Vitense (2b.Ob4.050)- He-abund. influences on late-type sp. Cannon (27.154.004)- faint nebl. near ct. JaCosta (2'.154.014)- surface-br. profi Ie Mallia to Pagel (22.064.u30)- evidence for mass loss from rG st. Persson et al. (27.154.002)- IR obs. of 82 rG st., spread in C[ abs. ~odgers et al. (26.114.012)- rG st. [Fe/HJ and S values from intermed. Dand oos. ROdgers t; ,'lewell (2d.034.0011- SI:C Vidicon photo of MS st. welcn £. Code "7.154.018)- DAD energy distrlb. C1339+260 (NGC 5272, M 3) Bell & DicKens (28.154.042)- chern. abund. via sp. synthesis Bendinelli et al. (21.154.042)- p.e. scan of core Corney (27.154.070)- age and oist. Christensen (21.114.039)- abs. sp. energy distrib. Cohen (J.) (21.114.565)- detaileo abuna. anal. of 3 rG st. Cohen (J.) et al. (21.113.042)- lR pe phot.; rG st. mlbol) and TIe) Cohen (N.) E; MalKan 125.154.003)- H20 maser err. search Cud"orth (26.154.014)- p.m. and memb. probe for 266 st. Dickey t; MalKan (27.154.016)- search for OH-em. Gopal-Krishna £. Steppe (28.141.024)- radio continuum obs. at 2.7, 4.8, and 10.7 GHz Gunn ~ Griffin (25.154.032)- rv (+ 1 km/s) for I I I rG and AGB st. Kanagy to ~yatt (22.154.001)- dust patches Mould & J'IcElroy (21.154.010)- TiD band str. Pilachowskl 122.154.010)- CO in rG st. Pilachowski et al. (27.154.006)- CC of rG st. i(ood (K.) et al. (22.141.092)- 1400 MHz radio sources Schneps et al. (22.154.029)- CO search Seiradakis & D.Graham (27.141.537)- 21-cm search for periodicities Spasaova (21.154.041)- p.m. of br. rG st. Suntzeff (27.154.025)- Ca-abuna. correlated with [Fe/H] Troland et al. (21.154.004)- unsuccesful search for CO weiCh & Code (27.154.018)- DAD energy distrib. C1343-511 (NGC 52(6) Fourcaae, Laborde & Aria (27.115.003)- CMD C140:.\+287 (NGC 5466) Dickey & Malkan 127.154.016)- search for OH-em. C1500-32a (NGC 5(24) dowers et al. (26.1~4.015)- 21-cm. ana 1612 MHz obs. for gas content C1514-208 (NGC 5897) welch & COde 127.154.01b)- DAD energy distrib.

STAR CLUSTERS AND ASSOCIATIONS

513

(~GC ')'1,,4, 1': ,) Cuney 1.::7.154.070)- age ana aist. Christensen (21.114.039)- ats. sp. energy aistrib. Cudwortn (2b.1~4.024)- p.rr. ana memO. proo. for 317 st. Dickey ~ MalKan (l7.1~4.01o)- search for DH-err. Pike (21.154.01~)- DDD electronog. oos. Pi lacnOWsKi (2.::.154.010)- CL in rG st. f'llachowski et al. (27.154.006)- CC of rG st. Se.raaaKis & Ll.Graham (27.141.537)- Zl-cm search for periodicities welcn i. Code (27.b4.016)- DAD enerllY aistrib.

C~j.l6+u2c

C1524-')0, (NuC j927) Alcaino (25.1')4.(,34)- CMD aowers et al. (2b.154.01~)- 1tlZ MHz

&

C1608+1~O

Cowley C1b14-22d Schneps Strauss

gos content

& Harvel

C154Z-376 Welcn

for

(NGC 5940) (20.154.011)- UBVK pe seq.

C15j1-504 Martins

~trauss

obs.

(NGC 5966) (ZZ.154.011)- multi-color strip photo Code (Z7.154.016)- DAD energy aistrib.

(Pal 14) et al. (21.114.010)-

sp. of rG st.

(NGC 6093, M 80) et al. (22.1:;'4.029)- CO search (Z2.154.0111- multi-color strip photo

C 1620-264 (NGC 61Z1, M 4) Moulo et al. (25.154.010)- TiD band-str. of reddest st. Scnneps et al. (22.154.029)- CO search ~elcn & Cooe (27.154.018)- DAD ener~y distrib. C1624-259 Alcaino

(NGC 6144) (27.154.009)- CMD

(NG~ 6171, M 107) Mould to. McElroy (21.154.010)- TiO Oand str. Pilachowski (22.154.010)- CO in rc' st. Seiraoakis i;. O.Graham (27.141.537)- 21-cm search for periodicities Troland et al. (21.154.004)- unsuccestut search for CO

C162~-129

COMMISSION 37

514

(;1639+3b5

(,~GC

62CJj,

M 13)

aetl t; DicKens (28.154.042)- chern. aound. yia sp. synthesis Carney (27.154.070)- age and dist. Christensen 1210114.(39)- aos. SP. enngy distrio. ,-onen (J.) (21.114.:)b')- detailed abund. anal. of 3 rG st. Cohen ( J . ) et al. (21.113.042)- IR pe phot.; rG st. m(bol) and TIe) Cudwortn (26.154.010)- p.m. and memb. prob., non-Yerkes plates Cuawortn £. Monet (25.154.033)- p.m. ana ~emb. prot., Yerkes plates DiCkey & MdiKan (27.154.016)- search for CH-em. GeraschenKo £. Kaala (25.154.006)- st. aistrib. in central region Gr iff i n (2 J • 11 ... \.I 36) - a iff ere n t i a I cur v e -0 f - II row t h [m I H) for r G st., L973 Kanagy £. ~yatt (22.154.001)- dust patChes ~ould £. McElroy (21.154.010)- TiD band str. Peterson, R.(27.154.066)- rG st. Na-abund. var. Pilachows~i (22.154.010)- CO in rG st. Ptlacnoroski et al. (27.154.006)- CC of rG st. Schneps et al. U2.154.029)- CO search Seiraaakis £. D.Graham (27.141.537)- 2l-cm search for periodiCities Spasaova (21.154.040)- p.m. of br. rG st. 5untzeff (27.154.025)- Ca-abund. correlated ",ith [Fe/H) van Aloada et al. (25.154.020)- ANS far-uv photo Welch £. Cooe (27.1'4.vlB)- OAO energy aistrib. C1644-0Hl (NGC 6216, M 12) duonanno et al. (21.154.035)- apparent distrib. of st. Gratton t; Nesci (21.154.009)- rv (-44 km/s) of cl. from indiv. st. MironoY, Samus' £. Shugarov (25.154.025)- instr. CMD Seiradakis £. D.Graham (27.141.537)- 21-cm search for periodicities weiCh t; Code (27.154.018)- DAD energy distrib. (1650-220 (NGC 623') Li Iler, M'(Z7.l54.0711- CMU C1654-040 (,'.jGC 6254, M 10) Buonanno et al. (21.154.035)- apparent distrib. of st. Gratton (28.154.017)- anal. of low-disp. sp. of rG st. Gratton & Nesci (21.154.009)- rv (+67 km/s) of cl. from indiv. st. Mould & McElroy (21.154.010)- TiG bana str. PilachowSKi (22.154.010)- CO in rG st. Seiraoakis ~ D.Graham (27.141.537)- 21-cm search for periodicities Welch £. Code (27.154.018)- GAO energy distrib. (NGC 6256) Alcaino (22.154.003)- CMD

~1656-370

C1658-300 (NGC 6266) Alcaino 121.154.028)- CMD C1659-262 (NGC 6273, M 19) Strauss (22.154.011)- multi-color strip photo

STAR CLUSTERS AND ASSOCIATIONS

C1702-220 (N~C 6267) Seiraaakis t. J.Graham (27.141.537)C1711-29~

(~GC

Moula et al.

63(4) (2,.1~4.010)-

~l-cm

TiD bana-str.

515

searCh for periodicities of redaest st.

C1715+432 (NGC 6341, M 92) Bell et al. (22.113.028)- Carbon unaerabuna. in st. br. than M(V)= -0.7 Bowers et al. (26.1,4.01,)- 21-cm. ana 1612 MHz obs. for gas ccntent Carney (27.154.0701- age ana aist. Christensen (21.114.0391- abs. sp. energy distrib. Cohen (J.I (26.114.0071- LTE line-blanketeo model atmosph. atuna. anal. of 4 st. Cohen (J.I et al. (21.113.042)- IR pe phot.; rG st. m(boll and T(e) Cowley et al. (21.114.0101- sp. of rG st. Dickens t. Gustaffson (2,.154.0111- rG st. Carbon abuno. Dupree et al. (25.154.017)- uv sp. Gopal-Krishna E; Steppe (280141.024)- radio continuum obs. at 2.7, 4.8, ana 10.7 GHz Gratton to Nesci (21.1,4.009)- cl. rv estimated from 3 inoiv. st. Pi I achowski (220154.010)- CO in rG st. Kood (R.) et al. (22.141.092)- 1400 MHz radio sources Seiradakis & D.Graham (27.141.5371- 21-cm search for periodicities $pasova (21.154.041)- p.m. of br. rG st. Suntzeff (27.1~4.0251- Ca-abund. correlated with [Fe/H] Troland et al. (21.154.0041- unsuccesful search for CD van AIOada et al. (25.154.020)- ANS far-uv photo welch E; eoOe (27.154.018)- DAD energy distrib. C171b-J.84 (N;;C 6333, M 91 Seiradakis & O.Graham (27.141.537)- 21-cm search for periodicities Strauss (220154.0111- multi-color strip photo 1.17 Z 0-177 (NG C 6356) Conen (N.) & MalKan (25.154.0031- H20 maser em. search C1724-307 (Terzan 2) Grinolay (22.142.0261- possible X-ray source Grindlay et al. (2B.154.012)- image of an X-ray burst MalKan et al. (27.154.063)- IR photo C1730-333 (Liller 1, MXB1730-333) Apparao ~ Chitre (Zb.154.0141- IR bursts MalKan et al. (27.154.063)- IR photo Cl732-447 (NGC ojC)b) aowers et al. (26.154.0151- Zl-cm. ano 1612 MHz obs. for gas content Strauss (2~.154.0111- multi-color strip photo

516

COMMISSION 37

C1136-536 (NGC 6397) Alcaino to w.Liller (Z7.154.07Z)- O\l.l to MS Bt!11 et al. (ZZ.113.0Z8)- Carbon underabund. in st. br. than M(V)= -0.7 JaCost .. (Z5d54.0l't)- surface-br. profi Ie Dickens & Gustatfson (2,.154.011)- rG st. Carbon abund. ,'1sll ia (22.154.021)- sp. of AGB st. Moule et al. (25.154.010)- TiD bano-str. of reOdest st. van Albada et al. (Z5.154.0Z0)- ANS far-uv photo C1735-032 (NGC 640Z, M 14) 6o~ers et al. (20.154.01~)- 21-cm. ana It1Z Mhz obs. for gas content Mould et al. (Z!J.l54.010)- TiD band-str. of reddest st. Welch t. Coae (Z7.1,4.018)- DAD energy distrib. C1742+031 (NGC 6426) DiCKey to Malkan (Z7.154.016)- search for DH-em. (NGC 6440) Bowers et al. (Z6.154.015)- Z1-cm. and 161Z MHz obs. for gas content Gopal-Krishna & Steppe (Z8.141.0Z4)- radio continuum obs. at Z.7, 4.8, ana IC.7 GHz Martins et al. (27.154.064)- surface photo SeiradaKis ~ D.Graham (Z7.141.537)- Zl-cm search for periodicities Shawl & R.E.~hite (28.154.004)- eq. cooro. of cl. center to ~ 1" Troiano et al. (21.154.004)- unsuccesful search for CO wi Illams & N.Bahcal J (26.154.006)- br.-, density- , ana color-profiles

C~746-Z03

C1746-370 (NGC 6441) Bowers et al. (2b.154.015)- 21-cm. and 1612 Mhz obs. for gas content Jernigan & Clark (Z6.154.00Z)- location of X-ray source Martins & Harvel (Z6.154.011)- UBVR pe seq. Shawl & R.E.White (28.154.004)- eq. coorc. of cl. center to ~ 1" Strauss (Z2.154.011)- multi-color strip photo C1751-Z41 (uKS 1) Malkan et al. (27.154.003)- lR photo (NGC 6535) Li Iler, M.(Z8.154.0Z31- BV CMD

C1801-D03

C!801-300 (NGC 6528) van den Bergh & Younger (Z6.154.013)- CMD, E(8-V); r, z C1804-437 (NGC 6541) Alcaino (Z5.154.00Z)- CMD van AltJada et al. (Z5.154.0Z0)- ANS far-uv photo williams f. N.Bahcall (Z6.154.006)- br.-, density-, and color-profiles C1806-Z59 (NGC 6~53) do~ers et al. (26.154.015)- 1612 MHz obs. for gas content Cohen (N.) & Malkan (Z5.154.003)- HZO maser em. search

STAR CLUSTERS AND ASSOCIATIONS

517

C1820-303 (NGC 6b24) Canizares et al. (22.1J4.000)- ptg., pe, and sp. uupree et al. (25.1J4.017)- uv sp. Jerniiian & Clark 126.1J4.002)- location of X-ray source Liller (M.) £. Carney (22.142.020)- CND Martins ~ Harvel (26.154.011)- U8VK pe seq. Martins & Harvel (27.1J4.007)- surface photo Rooo (R.) et al. (22.141.092)- 1400 MHz radio sources Seiradakis £. O.Graham (27.141.537)- 21-cm search for periodicities Shawl t. R.E.White (28.154.004)- eq. coord. of cl. center to.±. 1" .:imith, H.A. (27.1J4.065)- chem. abund. gradient Troland et al. (21.154.004)- unsuccestul search for CO Cld21-249 (NGC 6626, M 28) 8adailey 1.5 Jy at 2.7 GHz, all of which have been o~serve~ with ~he Cam~ridge 5 km synthesis telescope; for 93 percent, identificatIons WIth optIcal obJects have been possible and for 64 percent redshifts are available. A sim~lar catalogue of bright sources has been compiled for the frequency of 5 GHz by Kuhr et al. (81 AA Sup 45, 367). This covers both hemispheres down to a limiting flux density of 1 Jy at 5 GHz and includes 518 sources for which radio spectra and optical information is given. The .. catalogue is itsel f a subsample of a more extensive list of about 1800 sources (Kuhr et al. 79 MPlfR preprint No 55) and includes the ~ata from the most recent, and last section of the MPIfR "strong source" survey (Kuhr et al., 81 A.J 86, 854). The 5 GHz surveys have been extended to fainter sources by single-dish surveys complete to between 10 and 20 mJy (Pauliny-Toth et al. 80 AA 85, 329; Ledden et al. 80 AJ 85, 780; Pauliny-Toth et al. 81 AA in press). These surveys show that "convergence" of the source counts occurs at 5 (;Hz below 100 mJy. Statistical P(D) analyses of background deflections observed with the NRAO 9lm telescope (Ledden et al. 80 AJ 85, 780) and with the Effelsberg 100m telescope (I-faslo\\'ski et a1. 81 M 95, 285; Wall et al. 81 I-WI preprint No.l03) show that this convergence continues to a level of 'V 1 mJy and that no "new" population of sources appears at these low flux densities. Direct counts to levels as weak as 4.5 m.Jy have been made using background sources detected in 89 fields observed with the Westerbork Synthesis Telescope (Willis and ~liley, 79 AA Sup 37,397 & 79 M 76,65). These are roughly consistent with the P(D) results. The source counts at centimetre wavelengths are now satistically reliablej a considerable amount of information on radio spectra, identifications and redshifts exists. Studies of evolutionary models have been made and are continuing, and there is promise of considerable progress in this area over the next few years (eg. Wall 81 IAlJ Symp 97). In particular, ongoing observations with the Very Large Array are expected to extend the flux density range covered down to levels of some tens of lJJy. I II. BAS IC

~1EASlJRE~1ENTS.

a) Flux densities and radio spectra.

(R. FANTI, Bologna)

Flux density measurements at various frequencies for several samples of radio sources over a large flux density interval have been reported. Radio sources from the 4C catalogue, in the declination range 20° to 40°, have been extensively measured at several frequencies (Veron and Veron 79 AA Sup 36, 331 at 318 MHz; Veron et al. 81 AA Sup 43, 195 at 2.7 and 5 GHz; Katgert-Merkelijn et al. 80 AA Sup 40, 91 at 5 GHz). Flux measurements at 5 GHz for strong 82 sources (l! 1 Jy) are given in Grueff and Vigotti (79 AA Sup 35, 371) and Katgert-Merkelijn et al. (80 op.cit), and, for Ooty sources, by Gopal-Krishna and Witzel (80 AA 89, 169). 358 radiosources from the ± 4° declination strip of the 2.7 GHz Parkes catalogue have been measured at 408 MHz with the Bologna Cross (Grueff et al. 80 AA Sup 41, 21). High frequency observations of low frequency (408 - 1400 MHz) flat spectrum sources from the CB survey have produced high frequency spectra for about 200 sources up to 8 Gllz (Machalski and Condon 79 A.J 84, 164). Witzel et al. (81 A.J 84, 942) gIve flux densities for 345 sources of the NRAO-MPI 6 cm survey. At very weak radio fluxes (> 10 mJy) J. Katgert (79 AA 73, 107) has presented two-frequency spectra, between 1 ~4 and 0.6 Gllz for a complete sample of about 80 sources.

RADIO ASTRONOMY

A useful compilation containing spectral information has been produced by Kuhr et al. (MPIfR preprint No.55). are adjusted to the flux scale of Baars et al. (77 AA 61, containing sources stronger than 1 Jy at 5.0 Gllz has been 81 AA Sup 45, 367).

533

for over 1500 sources All the flux densities 99). A subset of it, publ ished (Kiihr et al.

A particular emphasis has been recently given to simultaneous multifrequency flux measurements, obviously in connection with radio variability (see e.g. Owen et al. 80 AJ 85, 351; Jones et al. 81 ApJ 243, 97; Mingaliev et al. 79 Astrofiz 14, 91) • b) Radio variability.

(R. FANTI, Bologna)

i) Flux monitoring. Galactic sources: A survey of variable galactic sources in the galactic plane is being made by Gregory and Taylor (79 JRASC 73, 303; 81 Ap.J 248, 596). SS 433 has been monitored at several wavelengths. Variations of a factor 4 in about 10 days have been found by Heeschen and Hammond (79 A.p.Jt 235,LI29). Bonsignori-Facondi (81 preprint), based on regular monitoring at 408 M~!z over more than a year, shows that the flux changes periodically, with the fundamental period of the object. Extragalactic sources: Results from monitoring of samples of compact « 1") extra galactic radio sources have been reported at several frequencies (Landau et al. 80 AJ 85, 363 for 55 sources and Epstein et al. 80 AJ 85, 1427 for 33 sources at 90 GIIz; Webber et al. 80 AJ 85, 1434 and Wardle et al. 81 AJ 86, 848 at 18 cm; Fanti et al. 79 AA Sup 36, 359 and 81 M Sup 45, 61 at 408 MHz; Condon et al. 79 AJ 84, 1 at 318 MHz; McAdam 80 PASAust 4, 70 at 408 MHz; Erickson and Fisher 81 ApJ 242, 884 in the range 0.3-1.0 GHz; Spangler and Cotton 81 AJ 86, 730 in the range 0.3-15 Gllz). From the above studies it appears now that variabil ity is equally common at all wavel engths. In particular, defin ite evidence has been obtained on the reality of variability at long wavelengths (J, > 20 cm.), on which doubts were often previously raised, both because of the lack of independent and simul taneous ohservations and because of the interpretational problems which are raised. Reviel\'s on variability of extragalactic radio sources and related probl ems are found in Fanti and Salvati (80 Proc. 5th [urop. reg. meeting astr., Liege) and Kellermann and Pauliny-Toth (82 ARAA 19, 373). Searches for variability in central components of double radio galaxies and quasars have been made by Hine and Scheuer (80 ~fN 193, 285) and by Hers et al. (81 preprint). Radio variability is found frequently in the case of radio galaxies and less frequently in the case of quasars, where, however, it tends to be hidden by larger measurement errors. ii) Time scale of variability. At all wavelengths variability occurs on typical intervals of few months to few years. At very short wavelengths daily and hourly variations have been searched by Epstein et al. (80 AJ 85, 1427). Most sources did not exhibit significant variations, but OV-236 showed a flux change by a factor 2.7 in a three day interval. At decimeter and meter wavelengths (Fanti et al. 79 AA Sup 36, 359; Spangler and Cotton 81 AJ 86, 730; Wardle et al. 81 AJ 86, 848) the fastest variations seen are of the order of 1 - 2 months. Brightness temperatures, deduced from the "causal ity" argument for sources varying at dm wavelengths generally exceed I012K by several orders of magnitude.

534

COMMISSION 40

iii) Spectral behaviour of variations. Epstein et a1. (81 preprint) have examined the outburst amplitude versus frequency in the mm and cm range. They find a variety of situations, ranging from cases where amplitudes are almost independent to cases were they are strongly dependent on wavelength. Still unclear is the situation of variahility at dm and m wavelengths. These phenomena, although being broad-band, seem disconnected with the cm variability (see Cotton and Spangler 79 ApJL 228, L63; Fanti et al. 81 IAU Symp 97). iv) Correlations with optical and X ray variations. Correlations with optical variability (Pollock et al. 79 AJ 84, 1658; Pica et al. 80 AJ 85, 1442) generally are inconclusive. In the case of PKS 0420-01 (Dent et al. 79 ApJL 227, L9) and of NGC 1275 (Lyutyi 80 Sov Astr L 6, 122) delays of about 2 years have been suggested between radio and optical variations, leading to the conclusion that the two phenomena occur in separate regions. In the case of 0235+164 (Balonek and Dent 80 ApJL 240, L3) and of 1921-29 (Gilmore 80 Nature 287, 612) a coincidence was seen between a radio and an optical outburst. The simultaneity in this case indicates a common origin. A search for X ray emission from variable radio sources using HEAO-l data has been made by Marscher et al. (79 ApJ 233, 498). The X ray fluxes expected on the basis of the time scale of variability are several orders of magnitude greater than the observed fluxes or limits, implying that sizes are larger than those deduced from time scale of variability. v) Polarization. Studies of linear polarization related to variability are presented by Aller et al. (81 AJ 86, 325) for 14 sources. The most impressive results are those showing rotation of polarization angle for 0727-115 and BL Lac, over substantially more than 180°. See also Altschuler (80 AJ 85, 1559) and Ledden and Aller (79 ApJL 229, Ll) for similar results. The suggested explanation is a rotation in the radio emitting region. The importance of circular polarization measurements for compact radio sources has been emphasized by Weiler and de Pater (80 AA 91, 41). They present a complete sample of compact sources for which circular polarization measurements are available and show that about a quarter of them are detected. For one source, 0316+162 (CTA 21), the change in sign expected as the source changes from being optically thick to optically thin is clearly seen. c) Brightness distributions. i) Extended sources.

(A. BRIDLE, Queen's Univ, Kingston)

With the addition of the VLA and MTRLI to the complement of image-forming radio telescopes and the development of procedures for high-dynamic-range mapping with the Bonn 100 metre radio telescope, the literature of structure measurements has become very extensive. Only a few aspects are mentioned explicitly here. The four major parts of typical extended sources are (1) small-diameter "cores" in the optical objects, (2) "jets" linking these to (3) diffuse "lobes" which in lowluminosity sources are relaxed in structure and limb-darkened but in higher-luminosity sources may contain (4) compact "hotspots" and are limb-brightened. Jets form the topic of Section (ii) below. For recent reviews of extended source structures see Miley (80 ARAA 18, 165) and Fomalont (80 IAU Symp 94). Sources which are distorted from the basic linear shape (I structure) of

RADIO ASTRONOMY

535

extragalactic sources may have either "inversion" or "mirror" symmetries (S or C structures). Ekers (81 IAU Symp 97), Ekers et al. (81 AA 94,61) and Shaver et al. (81 IAU Symp 97) examine the incidence of these distortions in complete samples of radio galaxies. They conclude that (a) the amount of distortion increases with decreasing radio luminosity, (b) S symmetry is most likely to occur in isolated multiple-galaxy systems and (c) rich cluster environments convert all morphologies to C symmetry. Total and polarized intensity distribution over many of the brighter and larger sources have been determined at several frequencies with resolutions of a few arc seconds or tens of arc seconds (e.g., Burch 79 MN 186, 293, 79 MN 186, 519 &79 MN 187,187; De Young et al. 79 ApJ 228, 43; Fanti et al. 81 AA 94, 61; Gioia and Gregorini 79 AA Sup 36, 347; ~IDgbom 79 AA Sup 36, 173; Laing 81 MN 194, 301 &81 MN 195, 261; Strom and Willis 80 AA 85, 236; van Breugel 80 AA 81, 265, 80 AA 81, 275, 80 AA 88, 248 & 80 Ph.D Thesis Leiden Univ; van Breugel and Willis 81 AA 96, 332; Willis et al. 81 AA 95, 250; Wright 79 ApJ 228, 34). High frequency mapping with single dishes has provided similar data at arc-minute resolution for some sources of large angular size (e.g. Klein and Wielebinski 79 AA 72, 229; Strom et al. 80 AA 85, 36; Wall and Schilizzi 79 MN 189, 593). These studies provide maps of spectral index, of Faraday rotation and depolarization and hence of projected magnetic fields, over the nearer and larger sources. These in turn constrain models of the energy flow through, and evolution of, the major parts of the extended sources. The 3C list is still the most intensively studied. New maps of 3C sources at one or more frequencies (in addition to those referred to above) have been given by Andernach et al. 79 AA 74, 93; Birkinshaw et al. 81 MN 197, 253; Bridle and Fomalont 79 AJ 84, 1679; Bridle and Vallee 81 AJ 86, 1165; Bridle et al. 81 AJ 86, 1294 &81 ApJ 248, 499; Burns and Christiansen 80 Nature 287, 210; Dreher 81 AJ 86, 833; Downes 80 MN 190, 261; Fomalont et al. 79 AA 76, 106, 80 ApJ 237, 418 &80 AJ 85, 981; Haschick et al. 80 ApJ 239, 774; Jones et al. 81 ApJL 247, L57; Kotanyi 80 AA 83, 245; Kronberg et al. 80 AJ 85, 973; Laing 80 MN 193,427; Lonsdale and ~brison 80 Nature 288, 66; Owen et al. 80 ApJL 239, Lll; Perley and Johnston 79 AJ 84, 1247; Perley et al. 79 Nature 281, 437, 80 AJ 85, 499 & 80 ~J 85, 649; Reich et al. 80 AA 89, 204; Rudnick et al. 81 ApJ 246, 647; Spangler and COok 80 AJ 85, 659; Wilkinson 81 IAU Symp 97; Willis and Schilizzi 79 AA 71,253. The structure of the radio galaxy Cygnus A has been studied over an exceptionally wide range of frequencies, from 150 MHz (Winter et al. 80 MN 192, 931) to 22 GHz (Berlin et al. 80 Pis'maAJ 6, 470; Dreher 79 ApJ 230, 687 &80 AJ 86, 833) and 150 GHz (Kafatos et al 80 ApJ 235, 18). There is no evidence for spectral steepening of the lobes from 1 GHz to 150 GHz, but a bridge of emission between the lobes is much stronger at 150 MHz than at 2.7 GHz. Four large-diameter sources were mapped at 43 and/or 74 MHz by Perley and Erickson 79 AJ 41, 131. Further examples of "giant" radio galaxies 1 Mpc or more in extent have been documented CHine 79 MN 189, 527; Masson 79 MN 187, 253; Mayer 79 MN 186, 99; Ulrich et al. 80 Nature 288, 459). Possible far-outlying components of 3C sources are reported hy Reich et al. 80 ApJL 235, L61; Salter and Haslam 80 AA 81, 240; and Stute et al 80 AA Sup 42, 299. The distinction between "compact" and "extended" sources made commonly in the literature, and for convenience in this report, has been shown to be artificial by the detection of low-level extended emission associated with luminous compact sources (Kapahi 79 AA 74, Lll; Kus et al. 81 MN 194, 527; Moore et al. 81 ~~ 197, 325; Perley and .Johnston 79 AJ 84, 1247; Perley et al. 80 AJ 85, 649; Wardle et al. 81 AJ 86, 848; Wilkinson 81 IAU Symp 97). Mapping surveys of clusters of galaxies have been made by Andernach et al. 80 AA Sup 41, 339 & 81 AA Sup 43, ISS; Burns and Owen 79 AJ 84, 1478; Burns and Ulmer

536

COMMISSION 40

80 AJ 85, 773; Burns et al. 81 AJ 86, 1; Gavazzi 79 AA 72, 1; Gavazzi and Perola 80 AA 84, 228; Kotanyi 80 Sup 41, 421; Harris et al. 80 AA 90, 283, 80 AA Sup 39, 215 & 80 AA Sup 42, 319; Perola and Valentijn 79 AA 73, 54; Perola et al. 80 AA 84, 245; Schallwich and Wielebinski 79 AA 71, L15; Valentijn 80 AA 89, 234; and Waldthausen et al. 79 AA Sup 36, 237). Singal et a1. (80 MN 191, 581) report lunar occultation studies of clusters. Detailed maps of "tailed" (C-shaped) sources in cluster environments have been made by Bridle et al. 79 AA 80, 201; Bridle and Vallee 81 AJ 86, 1165; Burns 81 MN 195, 523; Burns and Owen 80 AJ 85, 204; Burns et al. 79 AJ 84, 1683; Downes 80 MN 190, 261; Fanti et al. 81 AA 94, 61; Harris et al. 80 AA 90, 283; ~lcHardy 79 ~IN 188, 495; Owen et al. 79 ApJL 229, L59; Robertson 80 Nature 286, 579 & 81 AA 93, 113; Simkin and Ekers 79 AA 84, 56; Simon 79 MN 188, 637; Valentijn 79 AA Sup 38, 319, 79 AA 78, 367 & 81 AA 102, 53; Vallee et al. 79 AA 77, 183 & 81 ApJ November 1; and van Breugel 80 AA 81, 275. The real ity of very extended cluster "haloes" has continued to be controversial. That in the Perseus cluster has been shown to be an artifact of earlier low-resolution data (Birkinshaw 80 MN 190, 793; Gisler and Miley 79 AA 76, 109) whereas some others have been confirmed (Ballarati et al. 81 AA 100, 323; Hanisch 80 AJ 85, 1565; Hanisch and Erickson 80 AJ 85, 183; Hanisch et al. 79 AJ 84, 946). Jaffe and Rudnick (79 ApJ 233, 453) searched for new haloes. Structures of complete samples of quasars have been examined by Fanti et al. 79 AA Sup 35, 169; Potash and Wardle 79 AJ 84, 707 and Wills 79 ApJ Sup 39, 291. The "double quasar" 0957+561 A, B has been studied intensively in search of constraints on gravitational-lens models (Greenfield et al. 80 Nature 286, 865 & 80 Science 208, 495; Noble and Walsh 80 Nature 288, 69; Pooley et al. 79 Nature 280,461; Roberts et al. 79 Science 205,894). Structural information for samples of sources studied by the method of lunar occultations has been reported by Subrahmanya and Gopal-Krishna 79 Mem AS India 1,2; Singal et al. 79 Mem AS India 1, 14; Venkatkrishna and Swarup 79 Mem AS India 1, 25 and Joshi and Singal 80 MemAS India 1, 49. Sources from these samples have been studied interferometrically by Menon 80 AJ 85, 1577. Structures of sources identified with bright galaxies have been determined by Beck et al. 79 AA 72, 25 & 80 Nature 283, 272; Condon 80 ApJ 242, 894; de Bruyn and Hummel 79 AA 73, 196; Feretti and Giovaninni 80 AA 92, 296; Gioia and Gregorini 80 AA Sup 41, 329; Grave et al. 81 AA 98, 260; Hummel 80 AA Sup 41, 151 &80 Ph.D Thesis, Groningen Univ; Klein and Emerson 81 AA 72, 229; Kotanyi 79 AA 74, 156 &81 Ph.D Thesis, Groningen Univ; Kronberg and Biermann 81 ApJ 243, 89; Pfleiderer et al. 80 AA Sup 40, 351; van Albada 80 AA Sup 39, 283; van der Hulst et al. 81 AJ 86, 1175; Viallefond et al. 80 AA 82, 207. Structures of sources in disturbed galaxies have been determined by Fosbury and Wall 79 MN 189, 79; Ghigo 80 AJ 85, 215 and Kronberg et al. 79 ApJL 230, L194 &81 ApJ 246, 751. Structures of sources in Seyfert galaxies have been measured by Meurs and Wilson 81 AA Sup 45, 99; Ulvestad et al. 81 ApJ 247, 419; Ward et al. 80 MN 193, 563; Willis 79 AA 73, 354; Wilson 81 2nd ESO/ESA Workshop & 81 IAU Symp 97; Wilson and Willis 80 ApJ 240, 429 and Wilson et al. 80 ApJL 237, L6l. Extended structures associated with BL Lac objects are reported by Danziger et al. 79 MN 188, 415 and Weiler and Johnston 79 MN 190, 269. Other structure studies not referenced above include those of B2 radio galaxies by Grueff et al. 81 AA Sup 44, 241, of S4 survey sources by Kapahi 81 AA Sup 43, 381, of 4C sources by Rudnick and Adams 79 AJ 84, 437, of 4C sources with steep spectra by Tielens et a1. 79 AA Sup 35, 153, and of strong sources at 5 GHz by Ulvestad et a1. 81 AJ 86, 1010.

RADIO ASTRONOMY

ii)

Radio jets.

537

(A. BRIDLE, Queen's Univ, Kingston)

About seventy extragalactic radio sources are now known to contain bright, well-collimated radio features extending from unresolved cores at the centres of their parent optical objects towards their more extended radio emission. Such features are usually called "jets" (although there is no direct evidence for flow of matter along them). They have been detected in sources spanning the full range of radio luminosity from weak nearby galaxies to powerful quasars. The jets are commonly presumed to be due to radiative losses in or around "energy pipelines" linking the cores of active galaxies and quasars to their extended emission, as envisioned in continuous-beam source models (Blandford and Rees 78 Phys. Scr. 17, 265). Recent observations of the structures of large-scale (arcsec to several arcmin) jets in extragalactic sources have been reported by Birkinshaw et al. (81 MN 197, 253), Bridle (81 IAU Symp 97), Bridle et al. (79 ApJL 228, L9; 80 ApJL 241, L145; 81 ApJL 248, 499), Browne and Orr (81 in Opt. Jets in Galaxies, ESO/ESA Workshop), Burch (79 MN 186, 293; 79 MN 187, 187), Burns (81 MN 195, 523), Burns and Christiansen (80 Nature 287, 208), Burns and Owen (80 AJ 85, 204), Davies et al. (80 Nature 288, 64), Ekers et al. (81 AA 101, 194), Fanti and Parma (81 ESO/ESA Workshop), Feige1son (81 IAU Symp 97), Fomalont (80 IAU Symp 94), Fomalont et al. (80 ApJ 237, 418), Hogbom (79 AA Sup 36, 173), Jones et al, (81 ApJL 247, L57), Laing (80 MN 193, 427), Masson (79 MN 187, 252), Neff (81 IAU Symp 97), Owen et al. (80 ApJL 239, LIl), Perley (81 ESO/ESA Workshop), Perley et ·al. (79 Nature 281, 437; 80 AJ 85, 499), Potash and Wardle (80 ApJ 239, 42), Rudnick and Burns (81 ApJL 246, L69), Saunders et al. (81 MN 197, 253), Schrei'er et al. (81 ApJ in press), Vallee et al. (81 ApJ Nov. 1), van Breugel (80 AA 81, 275; 80 Ph.D Thesis), van Breugel and Willis (81 AA 96, 332), and Willis et al. (81 AA 95, 250). Properties of the large-scale jets are reviewed by Miley (80 ARM 18, 165), Willis (81 ESO/ESA Workshop) and Bridle (81 IAU Symp 97). VLBI observations of asymmetric small-scale (sub-arcsec) jetlike structures near the radio cores of galaxies and quasars have been reported by Cohen and Readhead (79 ApJL 233, LlOl), Cohen et al. (81 ApJ 247, 774), Cotton et al. (81 ApJL 244, L57), Kellermann et al. (81 AA 97, Lll. Linfield (81 ApJ 244, 436), Pauliny-Toth et al. (81 AJ 86, 371), Pearson and Readhead (81 ApJ 248, 61), Pearson et al. (80 ApJ 236, 714), Preuss et al. (80 ApJL 240, LID), Readhead (80 IAU Symp 92), Readhead and Wilkinson (80 ApJ 235, 11), and Simon et al. (80 ApJ 236, 707). Large-scale jets occur in 70% to 80% of sources in complete samples of nearby radio galaxies from the B2 and 3CR radio surveys, but the detection rate in more powerful sources is lower (Ekers et al. 81; Fanti and Parma 81; Bridle 81). Jets may therefore make-up a smaller fraction of the total luminosity in the more powerful radio sources. Observations of the internal structures of well-resolved jets show that they expand laterally at variable rates (Bridle et al. 79, 80; Bridle 81; Fanti and Parma 81, Feigelson 81; Perley et al. 79; Willis et al. 81). This presumably means that they are subject to some form of lateral confinement. Observations of linear polarization in large-scale jets are reported by Birkinshaw et a1. 81, Bridle et al. 79, 81, Burns 81, Burns and Christiansen 80, Burns and Owen 80, Fanti and Parma 81, Fomalont et al. 80, Laing 80, Owen et al. 80, Perley et al. 79, 80, Potash and Wardle 80, Saunders et al. 81, Vallee et al. 81, van Breugel 80a, b, van Breugel and Willis 81 and Willis et al. 81. In weIIresolved jets, degrees of polarization from 30% to 40% are common at wavelengths shorter than 2lcm, and polarizations as high as 65% have been detected (Willis et al. 81). Such high polarizations imply well-ordered magnetic structures in the jets. This is confirmed by direct mapping of the projected magnetic field

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structures in well-resolved jets (Bridle 81, Burch 79b, Fanti and Parma 81, Fomalont et al. 80, Willis et al. 81). The projected fields are generally either perpendicular to, or parallel to, the axes of extension of the jets; perpendicular fields dominate in jets produced by low-luminosity cores, while parallel fields dominate in jets produced by high-luminosity cores (Bridle 81). Elongated structures resembling abbreviated jets have been reported in two Seyfert galaxies (Booler et al. 81 MN in press; Johnston et al. 81 ApJL in press; Wilson 81 IAU Symp 97). iii) Compact sourc es (VL BI) .

(K.I.

KELLERM~~N,

NRAO)

Recent improvements in image formation techniques using radio telescope arrays having baselines of thousands of kilometers now permit pictures of compact radio sources to be made with resolutions better than one mill iarcsecond. "Closure-phase" or "self-calibration" techniques are used to eliminate the phase distortion introduced by the fluctuations in atmospheric path length (Cotton 79 AJ 84, 1122; Readhead et al. 80 Nature 285, 137; Schwab 80 SPIE J 231, 18; Rogers 80 SPIE J 231, 10). Multiple telescope arrays have been used at wavelengths ranging from 7 mm (Genzel et al. 79 ApJL 231, L73) to 91 cm (Simon et al. 80 ApJ 236, 707) to map quasars, galactic nuclei, interstellar molecular masers, and compact galactic radio sources. F~tragalactic sources: The observations of quasars and galactic nuclei generally show a core-jet morphology (Readhead 80 IAU Symp No.93, P 28; Pearson et al. 80 ApJ 236, 714; Readhead and Wilkinson 80 ApJ 235, 11; Wilkinson et al. 79 ApJ 232, 365; Kellermann 80 Ann Acad Sci N.Y. 336, 1; Pauliny-Toth et al. 81 AJ 86, 371; Baath et al. 81 ApJL 243, L123 & 80 AA 86, 364; Matveyenko et al. 80 Piz Astr Zh 6, 77; Preuss et al. 79 AA 79, 268; Readhead et al. 79 ApJ 231, 299; Kellermann and Pauliny-Toth 81 Ann RAA 19, 373). In a few cases, however, sources with a sharp low frequency spectral cutoff show compact symmetric double structure which is remarkably similar to the extended double sources (Phillips and Mutel 81 ApJ 244, 19 & 79 ApJ 236, 89). Of particular interest are the observations of apparent superluminal velocities in several quasars and galactic nuclei (Marsher 80 PASP 92, 127; Cohen et al. 79 ApJ 231, 293).

~1any classical extended radio sources also contain central compact sources which show the same core-jet morphology as the strong compact sources. In general these central components are coincident with the identified galaxy or quasar along the line joining the more extended structure (Linfield 81 ApJ 244, 436; Kellermann et al. 81 AA 97, Ll; Gopal-Krishna et al. 80 Nature 288, 344; Cohen and Readhead 79 ApJL 233, LlOl; Kapahi and Schilizzi 79 AA Sup 38, 11; Schilizzi et al. 79 AA

77, 1).

The compact structure in the double quasar 0957+561 has been mapped with various VLBI systems (Haschick 81 ApJL 243, L57; Porcas et al. 81 Nature 289, 758 & 79 Nature 282, 385). Relative positions of close pairs are being measured to submilliarcsec accuracy (Shapiro et al. 79, AJ 84, 1459). Several so-call ed "normal-galax ies" are al so found to conta in compact nuc lei which have been observed with VLBI techniques (Jones et al. 81 ApJ 246, 28; Graham et al. 81 AA 97, 388; Shaffer and Marscher 79 ApJL 233, LlOS). Structure ~ 0.1 arcsec has been found by VLBI in the hotspots of several extended 3CR sources (Kapahi and Schilizzi 79 Nature 277, 610 & 79 AA Sup 38, 11). Galactic sources: Compact galactic radio sources have also been observed with VLBI techmques. VtBI observat ions of SS433 show the same double structure seen at optical wavelengths. Motions are seen on a time scale of only one day (Schilizzi et al. 79 AA 79, L26 & 81 Nature 290, 318; Walker et al. 81 ApJ 243, 589.

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539

Spectroscopic VLBI observations of OH and H20 maser sources show a wealth of complex structure which gives important new insight into the location of the source of maser excitation and the process of star formation and evolution (Lada et al. 81 ApJ 243, 769; Haschick et al. 81 ApJ 244, 76; Bowers et al. 80 ApJ 242, 1088; Elmegreen et a1. 80 ApJ 241, 1007; Fix et a1. 80 ApJL 241, L9s; Reid et a1. 80 ApJ 239, 89; Downes et al. 79 AA 79, 233; Genzel et al. 79 AA 78, 239; Reid and . Moran 81 Ann RAA 19, 231). d) Optical and X-ray emission from extended sources. (G. K. MILEY, Leiden Observatory) Until recently our knowledge of the physics of extended extragalactic radio sources was obtained almost exclusively from the limited information that could be derived from radio continuum observations alone. During the last few years this situation has changed radically. Several observations have been made indicating the presence of appreciable optical and even X-ray emission from extended features (j ets and hotspots) in radio sources. In the case of radio hotspots, the correspondence of the radio and optical morphologies of the southern hotspot in the lobe of 3C 33 (Simkin 78 ApJL 222, Lss; Rudnick et al. 81 ApJ 246, 647) shows that at least in one hotspot there is a definite association of optical and radio emission. Radio-optical coincidences have been reported for other hotspots (e.g. Saslaw 78 ApJL 222,L3s; Crane et a1. 81 ApJ submitted) and statistical arguments suggest that some of these associations may be real. Optical observations of radio jets (Butcher et al. 80 ApJ 235, 749) have shown that the optical jets in M87 and 3C 273 are far from unique and X-ray measurements have demonstrated that the jets in M87 and Centaurus A have nonthermal spectra which probably extend continuously over more than eight decades of frequency (Schreier 81 Proc. 2nd ESA/ESO Workshop ''Optical Jets in Galaxies", p 109 and references therein). The presence of nonthermal continuum emission in the optical and X-rays argues strongly that relativistic particles in extended radio sources are accelerated within the lobes. Optical jets in radio galaxies was the subject of an ESA/ESO workshop in 1981. Not only do radio jets often have associated optical continuum emission but also since the last General Assembly a large body of evidence has shown that the relativistic plasma responsible for the synchrotron emission sometimes has emission lines closely associated with it. Detailed interrelationships have been found on a variety of spatial scales (e.g. Miley 81 2nd ESA/ESO Workshop p 9). Several connections have been established between the kiloparsec-scale synchrotron emission and the narrow-line regions of active galaxies. The radio luminosities are correlated with both the luminosities and the widths of the [0 III] lines (Wilson and Willis 80 ApJ 240, 429; Heckman et al. 81 ApJ 247, 403). Moreover, the line profiles indicate that the thermal material in the narrow line regions is flowing outwards (Heckman et al. 81 ApJ 247, 403). Detailed spatial correspondence has been observed between a radio jet and Ha emission on a scale of a few kiloparsec in the peculiar radio galaxy 3C 305 (Heckman et al. 81, in preparation). On a larger scale strong optical line emission extending over ~ 60 kpc was discovered from the lobes of the radio galaxy 3C 277.3 (Coma A) and these lines are closely connected with the knots and other features in the radio source (~Iiley et a1. 81 ApJL 247, Ls; Bridle et al. 81 ApJ 248, 499). The various observations of optical radiation associated \'!itll extended radio sources, combined with recent radio studies of Seyfert galaxies (e.g. Ulvestad et al.

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81 ApJ 247,419), have illustrated further the similarities which exist between Seyferts, rad io galaxies and QSOs and have reinforced the viewpoint in which all these phenomena are interpreted within the context of a unified scheme of active galaxies. Combination of radio and optical data provides a new method of studying particle acceleration processes as well as providing unique information about the physical conditions in the region of the extended radio emission. e) Pulsars.

(R.N. MANCHESTER, Radio Physics, CSIRO)

A total of 330 pulsars ranging in period from 33 milliseconds (the Crab pulsar) to 4.308 seconds are now known. In recent work a number of groups have investigated the pulse morphology, in particular, the pulse-to-pulse variations such as drifting subpulses and mode changing (e.g. Fowler et al. 81 AA 93, 54) and microstructure (e.g. Cordes et al. 81 ApJ in press). Weisberg et al. (81 AJ 86, 1098) searched for interpulses in a sample of 28 pul sars and found two at intermediate spacings. Flux densities and profile shapes measured at 102.5 and 61 Hllz by Izvekova et al. (79 Astron Zh 56, 322) show that most pulsars have a low frequency spectral turnover at about 100 HHz. Integrated pulse shapes and polarizations are given for a sample of southern pulsars in a series of papers (e.g. Hanchester et al. 80 HN 192, 153). Becker and Rankin (80 ApJ Sup 42, 143) have presented a statistical summary of the polarization properties of 18 pulsars which shows that the presence of orthogonal polarization states is almost universal. A number of interesting results have resulted from pulse timing observations by several groups. Helfand et al. (80 ApJ 237, 206) presented timing data on 37 pulsars recorded over an eight-year interval. Analysis of these results (Cordes and Helfand 80 ApJ 239, 640) showed that there is a correlation between the strength of random timing irregularities and pulse period derivative. Following a timing program by Newton et al. (81 MN 194, 841) in which new period derivatives were obtained for 124 pulsars, full timing data is now available for more than 90% of the kno~n pulsars. Three pulsars are now known to be members of binary systems (Taylor 81 'Pulsars', IAU Symp 95, p 361). The two recently discovered systems (PSR 0820+02 and PSR 0655+64) have almost perfectly circular orbits in contrast to PSR 1913+16 which has a highly eccentric orbit. In a recent paper Taylor and Weisberg (82 ApJ in press) describe in detail the observations of PSR 1913+16 which verify General Relativity to a high degree of precision, enable the determination of the mass of the pulsar and its companion (both close to 1.41 solar masses) and provide the first observational evidence for gravitational radiation. Establishment fo the distance scale is critical to any discussion of the galactic distribution of pulsars. Heasurements of HI absorption in the spectra of pulsars (Weisberg et al. 79 AA 77, 204 &80 AA 88, 84; Hanchester et al. 81 'Pulsars.., IAU Symp 95, P 445) have given new distance limits or estimates for 16 pulsars. Using a microwave link interferometer Salter et al. (79 Nature 280, 477) have for the first time made a direct measurement of the annual parallax of a pulsar (PSR 1929+10) giving a distance estimate of about 50 pc. A catalogue containing the prinCipal observed and derived parameters for the 330 known pul sars has recently been compiled by Hanchester and Taylor (81 AJ in press) .

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541

IV. RADIO TELESCOPES. a) Single dishes.

(A.T. MOFFET, Caltech)

Recent development of single-dish telescopes has been almost exclusively for observations at millimeter wavelengths. Notable new instruments have been the 7 metre antenna at Holmdel, New Jersey, and the first of the Caltech 10.4 metre antennas at Owens Valley, California. Each of these has been used effectively at wavelengths as short as 1.3 mm; the latter has a measured aperture efficiency of 0.42 at that wavelength (Wannier et al. ApJ 230, 149). Two larger telescopes have been readjusted or resurfaced to permit use of their central regions at millimeter wavelengths: the Effelsberg 100 m at A = 7 mm (Wielebinski 81 reported at URSI Gen. Assly) and the Parkes 64 m at A = 2.6 mm (Robinson 81 reported at URSI Gen. Assly). Large optical telescopes also continue to be used occasionally for millimeter and sub-millimeter observations (e.g. Kreysa et al. 80 ApJ 240, 117; van Vliet et al. 81 AA 101, Ll). In the next few years several new, large millimeter and sub-millimeter wave telescopes will begin operation. The largest of these is the 45 m dish at Nobeyama, Japan, with an r.m.s. surface error (0) goal of 200 microns. It will be used at its prime focus for wavelengths between 4 and 30 cm and at a Gregorian-coude focus for A < 4 cm. Its carbon fibre reinforced surface panels are mounted on motordriven positioners, and a laser surveying system is built in, permitting frequent readjustment of the surface (Tanaka 81 reported at URSI Gen. Assly.; also Nobeyama Rad. Obs. Tech. Rep. No.6). A 30 m telescope with expected surface accuracy o = 70 microns is under construction at Pico Veleta, Spain, by the Max Planck Institute for Radioastronomy. It will be operated, beginning in 1982, by the Institute for Radio Astronomy at Millimeter Wavelengths (I RAM) , Grenoble. A similar telescope will be built on Mount Korek, Iraq, By the Council for Scientific Research of Iraq. The Purple Mountain Observatory, Peoples' Republic of China, has begun the construction of a 15 m telescope in Chinghai Province, while the Science Research Council of the United Kingdom, with partial support from the Netherlands Foundation for Radio Astronomy, has designed a 15 m telescope (0 = 50 microns) which will be ruilt on I,launa Kea, Hawaii. The Raman Research Institute is constructing a 10.4 m dish (using the Cal tech design) at Bangalore, India. An improved Caltech 10.4 m, with 0 = 15 microns as a design goal, is under construction and will ultimately be located on Mauna Kea. The venerable Kitt Peak 11 m telescope will be resurfaced in 1982, becoming a 12 m with 0 < 100 microns. Notable advances have been made in the measurement of antenna surface profiles using RF techniques, either with transmitters in the near field or the far field (Mayer and Davis 81 reported at URSI Gen. Assly.; Godwin et al. 81 Int. ConE. Antenna & Propagation, York, lEE Conf. Publ. No. 195). Work has continued at NRAO on deformable subreflectors and on the effects of gravitational distortion on telescope performance (von Hoerner 80 IEEE Trans AP-28, 652). An absolute calibration of the effective collecting area of the Texas 5 m antenna at A = 3.Smm was carried out by Ulich et al. (80 IEEE Trans AP-28, 367). b) Millimeter-wave Arrays.

(A. T. MOFFET, Cal tech)

Several millimeter-wave interferometers designed for solar studies have been in operation for a number of years (e.g. Bordeaux, Kyoto). The first millimeterwave array capable of aperature-synthesis mapping of faint sources has been constructed at Hat Creek, California, and initial spectral-line maps from this instrument at A = 3.5 mm have been published (Welch et al. 81 ApJL 245, L87). A third 6 m antenna will be added to this array in 1982. Surface error profiles of

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the first two antennas have been measured with an accuracy of better than 100 microns using the holographic technique of Scott and Ryle (Welch 81 reported at URSI Gen. Assly.). The Owens Valley millimeter interferometer came into operation at A = 2.6 rom in 1981, using two 10.4 m antennas: a third will be added in 1982. The first successful VLRI observation at a wavelength as short as 3.5 rom was carried out between Hat Creek and Owens Valley in 1981. ~Iore powerful arrays under construction are those at Nobeyama (Ishiguro 81 Nobeyama Rad. OJlS. Tech. Rep. No.7), consisting of five 10 m dishes (0 = 150 microns) plus the 45 m described above, and that at Plateau de Bure, France, consisting of three 15 m dishes (0 = 50 microns), which is being constructed by IRAM. At 2550 m elevation, the latter will have the best site of all the millimeter arrays. The Nobeyama array will use a 320 MHz bandwidth, 1024 channel by 15 baseline digital Fourier transform correlator of advanced design (Chikada 81 reported at URSI Gen. Assly).

c) Aperture Synthesis Radio Telescopes.

(TIFR Centre, Bangalore)

The main developments that have taken place in the triennial period in various countries are summarised below. Australia - Sadly, the Australian Synthesis Telescope project still is not funded. However, during the period of this report the conversion of the E-W arm of the Molonglo Cross into the Molonglo Observatory Synthesis Telescope (MOST) which employs the fan-beam synthesis principle has been completed and the new instrument has commenced observations (Little 81 reported at URSI Gen. Assly). The telescope operates at a frequency of 843 Mllz, with a beamwidth of some 40", and an r.m.s. sensitivity of about 0.5 mJy is achieved in 12 hours. Developments are in progress on the Culgoora telescope to convert it to a correlator type instrument, with a subsequent increase in speed and flexibility. The Fleurs Synthesis Telescope is bein?, currently upgraded by the siting of additional 14 m antennae. The final resolution of the telescope should be improved to about 10" at 1415 ~lIlz (Frater et al. 80 Proc. Astron. Soc. Australia 4, 24). India - The Ooty Synthesis Telescope (OSRT), sited in the state of Tamil Nadu, is now in its final phase of construction. The telescope will eventually consist of ten small cyl indrical trough antennae and t",o 15 m parabol ic dishes used together with the existing large Ooty Radio Telescope. The configuration ",ill have a maximum baseline of 9 km E-I\' by 5 km N-S and operate at a frequency 0: 327 ~ll1z giving a resolution of 20" x 40" at declination 0°. Ohservations with the OSRT should begin with a 4 km maximum basel ine early in 1982. At Gauribidanur in the state of Karnataka, the decametric "T" antenna has come into operation during the past two years (Sastry et al. 81 J Astrophys. Astron. 2, 339). The telescope operates as a "~'ills Cross" instrument and has a resolution of 26' x 40' sec (0 - 14°) at its current operating frequency of 34.5 ~lllz. A scanning system automatically cycles the beam rapidly through eight chosen declinations in the range _30° < decl inat ion < +60°. Italy - The 408 ~lIlz "Croce del Nord" radio telescope at Medicina (Ficarra et a1. 77 Giornale di Astronomia 3, 115) has continued observations in this period. Initial astronomical results with the extended telescope used in its off-line aperture synthesis mode appeared in 1980 and the first parts of the 83 survey of radio sources are nearing completion.

RADIO ASTRONOMY

543

Netherlands - The Westerbork Synthesis Radio Telescope (WSRT) was used in its temporary "high-density" mode (40 simultaneous interferometers on a 1.5 km E-W baseline) until mid -1979, when two of the four moveable telescopes were transferred to their final positions. Since the spring of 1980, the instrument has operated on a 2.7 km baseline. It is intended to operate the WSRT at an additional frequency around 327 MHz in the near future. United Kingdom - The Multi Telescope Radio Linked Interferometer (~ITRLI) at Jodrell Bank came into operation in its full earth-rotation synthesis mode at the beginning of 1980 (Davies et al. 80 Nature 288, 64). This powerful instrument currently consists of six telescopes at different sites within the West of England and possesses a maximum baseline of 133 km. The system will operate at a variety of wavelengths between>. 73 cm and 1.35 cm giving resolutions between 1" and 0'.'02, although at the highest frequencies fewer telescopes than the maximum of six are useable. The large N-S component in many of the baselines guarantees a comparable resolution in E-W and N-S, even at low declinations. Observations of nearby calibration sources, of well known position, can be used to determine the phase of an observation in the presence of ionospheric and tropospheric uncertainties, however great success has been achieved using the closure phase relationships between different combinations of the telescopes to produce maps (Cornwell and Wilkinson 81 MN 196, 1067). The telescope is noteable for its high dynamic range mapping where at least 1000:1 has been achieved. Observations of source polarization and spectral lines should soon be available.

At Cambridge the 5 km Telescope has been operated at a frequency of 31.4 GHz giving a resolution of about 0'.'35 (Scott 81 MN 194, 24p). The efficiencies of the individual 13 m antennae are between 20 and 25% and instrumental phase stability is good. Observations for the 6C survey of radiosources at 151 MHz have been completed in this period. These possess a resolution of 4' x 4' cosec (0)' The resiting and extension of this array to a maximum baseline of 4.6 km has taken place and initial observations with the revised instrument are underway. A special purpose experiment was made to map the strong radio galaxy Cygnus A at 151 MHz (Winter et al. 80 MN 192, 931). Using a fixed and a portable antenna, interferometer spacings upto 15,674 A ("'30 km) were observed. As phase stability was not possible due mainly to the ionosphere, in the reduction of the data source symmetry was assumed (a reasonable assumption in the case of Cygnus A) permitting the assignment of phase necessary for image reconstruction. The final resolution of the map was 10" x 16". U.S.A. - The completion of the construction phase of the VLA ~ery Large Array) on the Plains of San Augustin, near Socorro, New Mexico was marked by the dedication of the telescope on October 10, 1980. The completed instrument is described in detail by Thompson et al. (80 ApJ Supl 44, 151). The instrument has since been in regular use for hoth the quasi instantaneous (snapshot) and full earth-rotation synthesis mapping of astronomical objects. ~Iapping in spectral line mode is available to users, as well as the observation of total power and polarization characteristics of the continuum emission from radio sources. Since completion, the array has been used in each of its four standard configurations. These have maximum baselines from the phase centre of 21, 6.4, 1.95 and 0.59 km and it is intended to cycle through them over approximately 15 month periods. I\t present observations can be made in the A 21 - 18, G, 2 and 1.3 cm hands and it is planned that a band near A 92 cm should shortly be available. Among the important developments in map restoration techniques made for use with VLA data, the efficient implimentation of the CLEAN algorithm (Clark 80 AA 89, 377) and the employment of closure phase, or "self cal ibrat ion", techniques to produce improved quality maps in the presence of amplitude and phase fluctuations (Schwab 80 SPIE Proc. Vol 231; Graham 82 in preparation) can be mentioned. Such developments have permitted the achievement of very high dynamic range mapping.

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The "TPT" decametric array of the Clark Lake Radio Observatory near Borrego Springs, California is now in full operation. Originally the E-IV arm was used alone as a fan-beam synthesis telescope (Perley 79 AJ 84, 1443). The final, fullysteerable array is described in Erickson et a1. ~2 ApJ in press). The array is a "T" of 720 conical spiral antennae (teepee shaped) and has dimensions of 3.0x 1.8 krn. It will operate between 15 and 125 ~lIIz, with best sensitivity in the range 25 to 75 HHz. Both the operating frequency and beam position are adjustable in about 1 msec. A 1024-channel digital correlator has been built and attached to the array. This permits the simultaneous measurement of the complex visibility functions of 512 interferometric basel ines between various portions of the array. After Fourier transformation, these visibility data yield a 32 x 32 resolution element picture of the observed area of sky. The frequency dependent angular resolution ranges from 17' to 3', with a sensitivity of about 1 Jy. U.S.S.R. - The 10\\' frequency "T" radio telescope, lITR2, of the Grakovo Radio Astronomy Observatory has continued its survey of radio sources between 10 and 25 fvlEz (Braude et a1. 80 preprint No.147, Kharkov). Proposed equatorial radio telescope - Among proposed projects for future aperture synthesis telescopes, that concerning the Giant Equatorial Radio Telescope (GERT) perhaps deserves special mention. This design study promotes a scheme that, amongst other objectives, would construct a synthesis telescope consisting of a large cylindrical parabolic trough (size 2 km x 50 m) and fourteen small cylindrical antennae (size 15 m x 50 m). The longest basel ine would be 14 krn E-II' by 12 krn N-S, glvmg a resolution of some 10" at 325 HHz. The project would be a cooperative effort between nations of the developing Mlrld and the telescope would be constructed on the terrestial equator. Possible sites are in Indonesia and Kenya. The full proposal is described by Swarup, Odhiambo and Okoye (79 INISSE and GERT: a proposal, Tata Press, Bombay). d) Very Long Baseline Interferometry (VLBI).

(R. S. BOOTH, .Jodrell Bank)

The comprehensive review of VLBI by Hoffet in the 1979 report of Commission 40 will be taken as a starting point for this report. The past 3 years have seen a consolidation of the situation described by Moffet and the development of the technique to a point where experiments may be conducted by non-specialists. The major advance in the past 3 years is the implementation of the wideband VLBI system (Coates et a1. 75 Tectonphys 29,9). This, so called ~lk III system was developed jointly by NASA (Goddard Space Flight Center), Haystack Observatory, NRAO, and ~nT, for application to geodesy and radio astronomy. It is now used regularly in network experiments. The VLBI networks - Networks of telescopes in the USA and in Europe now operate at regular intervals (8 days every 2 months in the USA and a similar period 4 times a year in Europe) to conduct high resolution observations of radio sources. Both net\\'orks are managed by representatives from the participating observatories and have been operated with great success over the past 3 years. Global experiments combining some or all of the telescopes in both networks have also become common. The wavelengths successfully used by the networks have covered most of the RF band from 50 cm to 7 mm. The US network has now been operational for more than 5 years. Recently compiled statistics by Moran show that more than 200 experiments have been conducted involving about 120 investigators from 33 different institutions. Highlights among the results from the US network in the past 3 years are the hybrid maps by the Caltech group, particularly those of the superluminal source 3C 273 (Pearson et al. 81 Nature 290, 365) and the measurement of proper motions among H20 maser components (e.g. Genzel et a1. 81 Ap.J 244, 84).

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545

Operation of the European network on a regular basis began in 1980 although ad hoc experiments have been conducted since 1976. The network is in great demand, its particular attribute being the high sensitivity achieved when Effelsberg, I'lesterbork and the Jodrell Bank Mk IA telescope are used. A further addition to this network is the Polish 15 m telescope in Torun. A 6 cm receiver is available at Torun and receivers for 18 cm and 21 cm are under development. The Italian group also expect to join the network in 1982 and 30 m antennas are being built at Bologna and in Sicily. Highlights among the European achievements are the results on the double quasar (Porcas et al. 81 Nature 289, 758) and SS433 (Schilizzi et al. 81 Nature 290, 318). The Canadian VLBI system has also continued to be used. In the Soviet Union a narrow band 1.35 cm wavelength VLBI system has been set up between Crimea and Puschino, based on the 22 m telescopes at the Crimea Astrophysical Observatory and the Lebedev Physical Institute (Matveenko et al. 80 Sov Astron Lett 6, 662). Both stations have 70 K maser receivers and Hydrogen maser frequency standards. The 1150 km baseline has been used to resolve several water maser sources. The Mk III system - This system represents a major increase in sophistication and sensitivity in VLBI. It is a wideband (56 MHz) digital system based on multi-track instrumentation recorders. The data acquisition terminal is computer controlled and takes a broad band IF signal, converts selected frequency windows to video (baseband), separately clips, samples and formats each video signal and records the resulting time-tagged, Mk III serial data streams, in parallel on magnetic tape. The terminal contains the control computer and includes phase and cable calibration among its facilities. (This is especially useful for astrometry and geodesy.) Twenty eight parallel data streams are recorded simultaneously on magnetic tape at speeds from'" 17 in/sec to '" 270 in/ sec depending on the bandwidth. With a bandwidth of 56 MHz, each tape lasts for only 20 minutes and this represents something of a problem. Work is continuing in this area to produce stacks of heads with widths as small as 40 microns. The head-stack will be inched across after each pass of tape and multiple pa'ss recording will be adopted. It is hoped that such a modification will increase the total recording time per tape to 3 hours. Mk III recording terminals are currently available at OVRO, Fort Davis, Haystack, NRAO (140 ft and VLA), Onsala. and Effelsberg, and terminals will be acquired by the Naval Research Labs (Maryland Po int), Westerbork, Nobeyama (Japan), Jodrell Bank and Bologna. A 3-station Mk III processor is available at Haystack Observatory and processors are being constructed at JPL/Caltech and MPI, Bonn. An exciting example of the value of the increased sensitivity provided by the Mk III system is the detection of the predicted 3rd component of the double quasar with a flux density of 1 mJy at 13 cm. (Gorenstein et al. 81 IAU Telegram No.3644). Other activities - The importance of VLBI has led to several design studies to improve the existing networks. Dedicated arrays of telescopes spaced to adequately fill the u-v plane have been proposed for Canada (Legg (ed.) 1979, NRC report) and for the USA in a Ca1tech study (Cohen (ed.) 1980 "A Transcontinental Radio Telescope") and a study at NRAO 1981 (The Very Long Baseline Array Design Study). A further design study is underway in Canada. Representatives of the European community have been conducting an ESA sponsored study of a real time VLBI system based on communication links with a geostationary satellite (LAST) (1981 ESA Report SCI (81) 5). To this end van Ardenne et al.

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(81, NFRA report) have carried out a phase comparison experiment using a 2-way communications 1 ink via a satell ite. Link precision was found to be better than 10 psec over intervals in the range 10-1000 sec - a better stability than a Rubidium standard. They suggest that a 1 ink performance exceeding the capabil ities of present hydrogen masers could be achieved. Unfortunately financial 1 imitations will prevent the implementation of this \',-ark. V. RAD IO ASTRONmlY

INSTRU~IENTATION

.

(N.V.G.

SA~~A,

RRI,Bangalore)

a) Low noise receivers for centimetre and dec imetre wavelengths. GaAs FET amplifiers operating at cryogenic temperatures « 15 K) have no\',' achieved noise performance comparable to that of parametric ampl ifiers for frequencies upto 15 Gllz. Noise temperatures of < 10 K at 1.4 GHz and 20 K at 4.5 Gllz over a bandwidth of 500 ~IHz have been reported (Burns 78 NRAO EDIR 197; VOldnkel 80 Electron Lett 16, 730; I':illiams et al. 80 ~Iicrowave Journal 23(10), 73; lieinreb 80 IEEE Trans ~ITT-28, 1041; Weinreb et al. ~RAO EDIR 220). GaAs FET amplifiers are simpler to build and are much more stable compared to paramps. ~Ioreover, simultaneous power and noise match of the input of the FET ampl ifier obtained by adjustment of the source lead inductance eliminates the need for circulators at the input port. Ibruegger U,IPIfR) and Il'ellington (CSIRO) have reported noise temperatures of ahout 50 K for cooled GaAs FET amplifiers operating at 10.7 Gllz and 15 GHz (NRAO Greenbank Instrumentation Workshop, September 1981). A reflected-wave maser employing a unique design in which four stages are cascaded via ten circulator junctions and operating at 4.6 K in a three stage closed cycle Hel ium cryostat achieved a tuning range from IS.3 to 26.6 Gllz, net gain of 30 dB and an instantaneous bandl,ridth of 240 Mllz near the band centre. The measured noise temperature of this maser was 13 ± 2 K referred to the room temperature input flange (r>loore and Clauss 79 IEEE Trans ~lTT-27, 249). A travell ing wave maser developed in Sweden has a tunable frequency range from 29 to 35 Gllz, an instantaneous bandwidth of 60 ~llIz and an input noise temperature of about 35 K (Kollberg 80 IAU Symp 87, 615). b) Mill imetre wave receivers. There has been a remarkable progress in Schottky barrier diode mixers for operation beyond 200 Gllz. This was made possible by the development of improved GaAs mixer diodes (Linke et al. 78 IEEE Trans MTT-26, 935; Keen et al. 79 Electron Lett IS, 689) and a better understanding of mixer theory (Held and Kerr 78 IEEE Trans ~ITT-26, 49; Kerr 79 IEEE Trans MTT-27, 938). Room temperature Schottky diode mixers with a quasi-optical local oscillator injection technique have been reported to give good performance upto 670 GHz. Typical mixer noise temperatures (SSB) of 1800 K at 200 GHz, 2600 K at 300 GHz and l2000K at 670 GHz have been achieved (Fetterman et al. 78 Appl Phys Lett 33, 151; Wrixon 78 Conf Digest, European Microwave Conference, 717; Carlson et al. 79 IEEE Trans MTT-26, 706; Erickson 81 IEEE Trans MTT-29, 557). Cooled Schottky diode mixers gave mixer noise temperatures (SSB) around 100 K at 100 GHz (Keen et,al. 79 Electron Lett IS, 689; Weinreb and Mattauch 79 Proc Nat Radio Science meeting, URSI, Boulder)and 300 K at 230 GHz (Archer and ~lattauch 81 Electron Lett 17, 180). Super-Schottky diode mixers have also been developed for millimetre wavelengths ~cColl et al. 79 IEEE Trans MAG-IS, 468) and give a mixer noise temperature around 10 K at 30 GHz. Millimetre wave mixers using superconductor-insula tor-superconductor (SIS) tunnel junctions as mixing elements have been found to give low noise performance with very low local oscillator power of a ~W or less (Dolan et al. 79 Appl Phys

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Lett 34, 347). There now exists a quantum mechanical theory (Tucker 79 IEEE J Quan Electron 15, 1234) for these superconducting mixer devices, and it predicts conversion gain and quantum limited noise performance. These predictions have since been qualitatively verified experimentally (Shen et al. 80 Appl Phys Lett 36, 777; Phillips et al. 81 IEEE Trans ~~G-17, 684; Rudner et al. 81 J Appl Phys 52, 6366). Mixer noise temperatures of 9 ± 6 K at 36 GHz with a conversion gain of 4 dB, and 60 K at 115 GHz with a convers ion loss of 7 dB have been reported. Negat ive differential output impedence has been observed which can lead to possible infinite available gain (Kerr et al. 81 Physica 108B, 1369) at 115 GI-Iz. At 230 GI-Iz, the best mixer noise temperature achieved so far is around 300 K (Phillips et al. 81 IEEE Trans MAG-17, 684) and this relatively poor performance has been attributed to the inadequate supression of Josephson currents by the applied magnetic field. Single junctions and also arrays of junctions have been tried in the above experiments. Superheterodyne receivers at 2 mm and 3-4 mm using Josephson mixers as front ends were developed in the USSR (Abljazov et al. 81 Radiotekhnika: Electronica 26, 167; Kislyakov et al. 81 Zh Tech Fiziki 51,1737). Sensitivities of 0.3 Kat 2.2 mm (bandwidth 300 MHz, time constant 1 sec) and 0.03 K at 3-4 mm (bandwidth 30 GI-Iz) were achieved. Low noise receivers using bulk devices as detector elements have also been developed to operate at short millimetre and submillimetre wavelengths. A bolometer cooled to 0.3 K has been successfully operated at 1.2 mm wavelength (Payne, Green Bank Instrumentation Workshop, September 1981) on the NRAO 36 ft dish at Kitt peak. This gave a minimum detectable temperature of 2 mK for a 1 second integration time. An InSb hetrodyne receiver has been operated at 492 GHz to detect the fine structure transition of atmoic Carbon (Phillips et al. 80 ApJ 238, Ll03). The receiver noise temperature was about 350 K at 500 GHz. The instantaneous bandwidth is only about 1 MHz and hence the spectra were taken by sweeping the local oscillator. A receiver operating between 460 and 500 GHz using an InSb crystal as the mixing element ~an VI iet 81 Ph.D Thesis, University of Utrecht) with a noise temperature of about 1000 K has been used to detect the CO J = 4 + 3 transition. At short millimetre and submillimetre ~avelengths, generation of sufficient local oscillator power is a problem, and this has been partly solved by the development of Schottky diode multipliers (Schneide'J' and Phillips 81 Int J Infrared mm waves 2, 15; Archer 81 IEEE Trans MTT-29, 552; Erickson 81 IEEE Trans MTT-29, 557). For doublers, efficiencies of 15% have been achieved for the output frequency range of 190 to 230 GHz. For triplers, a peak efficiency of 6% has been achieved for the output frequency range of 200-240 GHz. Quasi optical components for the short millimeter wavelength range have been developed for such functions as diplexing, beam splitting, band rejecting and focussing (Payne and Wordemen 78 Rev Sci Instrum 48, 1741; Nakajima and Watanabe 81 IEEE Trans MTT-29, 897; Van Vliet 81 Ph.D Thesis, University of Utrecht). These components exhibit lower losses than conventional components. c) Correlators and Spectrometers. Wideband autocorrelation spectrometers are now in operation at several observatories. A 256 channel 3-level autocorrelator has been built in South Africa (Woodhouse 80,Trans S African lEE 71, 188). The VLA Correlator consists of 702 wideband digital spectrometers (Review of Radio Science, URSI 81, J2). However, filter bank spectrometers are still the mainstay at millimeter wavelengths. Acousto-optic spectrometers (AOS) are showing great promise to replace the filter banks at millimeter wavelengths and there are several operational AOS systems around the world (Milne and Cole 79 Proc IREE Australia 40, 43; Chikada et al. 80 IAU Symp 87, 625; Mason 80 Proc Soc Photoopt Ind Engrs 231, 291). The

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characteristics of three large bandwidth systems are tabulated below.

Parameter

CSIRO

AOS Model Tokyo

Ca1tech

Overall Bandwidth: MHz

270

220

100

Resolution: KHz

256

275

160

1050

1728

1024

Number of Channels

Some of the above ADS systems are in regular use on radio telescopes and are reported to give a very nominal degradation of signal to noise ratio compared to conventional filter bank spectrometers. VI. DATA PROCESSING.

(C.R. SlIBRAlIMANYA, TIFR Centre, Bangalore)

This section deals mainly with some important developments during the past 3 years on the reduction of aperture-synthesis observations. The basic methods of restoration have been reviewed by Bracewell (79 Ann Rev AA 17, 113) and Subrahmanya (80 Bull Astr Soc India 8, 5). The recent emphasis has largely been on implementing proper calibration schemes, taking into account the systematic errors and noisestatistics. This has indeed proved to be highly rewarding as witnessed by the quoted dynamic range of ~104 for a synthesis map of NGC 1275 made at Westerbork (Oort 81 reported at IAU Symp 97). Another striking application of the new techniques can be seen in the maps produced with the multi-telescope radio-linked interferometer (MTRLI) at Jodrel1 Bank using the hybrid-mapping program CORTEL (CORrecting TELescopes, e.g. Readhead et al. 80 Nature 285, 137). It appears from these results as well as some ~lind-tests' performed by Cornwell and Wilkinson (81 MN 196, 1067) that one can now attempt reliable hybrid-mapping from interferometers with poor amplitude-stability and complete phase-instability. A dynamic range of about 50 seems to be quite feasible even in the absence of phase measurements for the maps of stronger complex sources observed with MTRLI. This is not too far from the typical dynamic ranges attained till a couple of years ago with well-calibrated measurements. The hybrid mapping technique, originally intended to ensure closure-phase relation has now been extended considerably (e.g. Cornwell and Wilkinson 81 MN 196, 1067; Noordam 81 Proc ESC) Conference on "Scientific Importance of IIigh Angular Resolution at Infrared and Optical Wavelengths" Garching). The central theme of the recent techniques is that although the observat ions with an interferometer g lve vis illi1 it ies for each basel i ne, the number of independent measurements at any given time is no more than the number of individual telescopes used in the system, which therefore should also be the number of constraints imposed on any solut ion by the measurements. This has been used to correct for instabil ity in the telescope phase or gain and to provide estimates of phases in the absence of phase-calibration. Essentially, one starts with some model to provide an estimate of visibilities which is updated by imposing suitable constraints to provide an antenna-based solution. This is then used to improve the model (usually through CLEAN) and the process repeated till convergence. The method appears to be quite rugged. It is remarkable that, starting from an initial guess of a single point source, CORTEL converges to a realistic solution in about 20 iterations in a completely phase-unstable situation (Cornwell and Wilkinson 81 op cit). The hybrid mapping scheme (self-cal) at VLA uses the first few components of CLEAN to provide

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an initial guess (Schwab 80 SPIE Proc Vol 231). A similar scheme is used in the Netherlands where the high degree of redundancy provided by the regularly spaced antennas of WSRT is used to achieve a high dynamic range (Noordam 8i op cit). An efficient scheme has been suggested by Clark (80 AA 89, 377) for implementing CLEAN on computers with limited memory but good computing power through an array processor. The purpose is to save the time normally wasted in accessing the dirty beam from the disk when one is CLEANing a large map. Imaging from incomplete measurements has been reviewed in the context of several subj ects in the book ed i ted by Herman (79, "Image Reconstruct ion from Projections: Implementation and Applications", Springer Verlag, New York). The book also includes a chapter by Bracewell on the problem in radio astronomy. There has been a continued effort in demonstrating the improvement in restoration provided by use of prior knowledge like positivity and sharpness/smoothness of images. Typical examples of methods for implementing prior knowledge explicitly can be found in the "Optimum Deconvolution Method" (Subrahmanya 80 AA 94, 85) and in a scheme using Simplex method (Baker 81 AA 94, 85). Maximum entropy method (MEM) has been extended by Bryan and Skilling (80 MN 191, 69) to noisy situations by forcing the residuals to have the known statistics of noise. They have shown that this results in an improved restoration. There is a growing belief that one should not attach too much significance to "entropy" in MEMbut look upon MEM as one of the ways of ensuring consistency with measurements and prior knowledge like positivity. It appears that a wide variety of functions satisfying some general mathematical requirements can efficiently play the role of "entropy" in MEM (Nityananda and Narayan, RRI Banga10re, in preparation). As the attempts towards phaseless reconstruction, super-resolution and exceptionally high dynamic ranges are becoming more and more common, it is now very important to examine the question of reliability more thoroughly. The existing simulations or "blind tests" are perhaps too simplistic to lead to specific conclusions on reliability to the accuracy demanded by recent developments. A measure of reliability based on properties of the residuals and the derived solution will be of great value. Mention should also be made of the standardization of a format "FITS" (Flexible Image Transport System) for the interchange cf astronomical images and other digital arrays on magnetic tape (Wells et al. 81 AA Supp1 44, 363; Greisen and Harten 81 AA Suppl 44, 371). It provides a simple and powerful mechanism to generate self-documenting data tapes for the unambiguous transmission of n-dimensional, regularly spaced data arrays.

G. SWARUP President of the Commission

COMMISSION 41:

HISTORY OF ASTRONOMY (HISTOIRE DE L'ASTRONOMIE)

PRESIDENT: M.A. Hoskin VICE-PRESIDENT: O. Pedersen ORGANIZING COMMITTEE: S.M.R ..Ansari, J. Dobrzycki, J.A. Eddy, E.G. Forbes (representing Division of History of Science of IURPS), P.G. Kulikovsky At the end of the General Assembly in Montreal, the membership of Commission 41 comprised 79 full members and 32 consulting members. Many of the consulting members, not being professional astronomers, find it difficult to attend the General Assemblies in person. As a result, the most valuable activities of the Commission lie in the initiation and organization of ongoing projects and the sponsoring of specialist meetings, while the sessions at General Assemblies are most successful when they are also of interest to astronomers outside the Commission. A significant development in organization has come about with the formation of the History of Astronomy Division of the American Astronomical Society. A further sign of fruitful interaction between astronomers and historians has come with the invitation to an historian to give an Invited Discourse at the forthcoming General Assembly. Much of the effort of the world-wide community of historians of astronomy has been devoted to the General History of Astronomy (GHA), which is jointly sponsored by IAU and IURPS and is being published by Cambridge University Press. GHA is planned as a four-volume work, but each volume will be issued in either two or three parts. This is for the convenience of librarians, but it does reduce the delays resulting from defaulters among the authors. It is expected that the first part will be sent to the printer early in 1982, and that two or more parts will follow each year. The "Greenwich List of Observatories", organized by H.D. Howse and compr~s~ng a detailed catalogue of observatory instruments in the period down to 1850, is now almost complete. It is designed for inclusion in vol. 3 of GHA, and will be a major reference work for the history of astronomical instruments. A significant development in the period under review has been the microfilming of archives for sale to interested institutions, these primary materials thereby becoming generally available to historians, The papers of William, John and Caroline Herschel held by the Royal Astronomical Society are now available on microfilm, and the correspondence of Ejnar Hertzsprung is to be published on microcard; and it is hoped to make the papers of the third and fourth Earls of Rosse similarly available. Access to such materials at institutions scattered throughout the world is a major stimulus to historical research, and if the sale price is chosen so as to allow for some contribution to the initial outlay, the cost to the owners of the papers is small. Intense interest continues to be shown in 'archaeoastronomy'. An Archaeoastronomy Bulletin is published in the USA, and J. Hist. Astron,now has a fourth issue each year which is designated the Archaeoastronomy Supplement. A remarkable number of books and articles have appeared dealing either with megalithic astronomy or with archaeoastronomy of the New World, and several conferences have been held devoted to one or other area. The methodologies required are however very different. In the New World, it is possible, even necessary, to consider written evidence and oral traditions in addition to examining the archaeological remains, and the 551

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approach is inevitably interdisciplinary. By contrast, the evidence from the megalithic culture consists very largely of stone remains, whose purpose has to be inferred from archaeological and astronomical considerations. As the stones have often been disturbed, statistical treatment is required. Many archaeologists find the astronom~cal and statistical techniques difficult of access, while the mathematicians and astronomers sometimes blunder in matters of archaeology. Yet in both cases, because of the paucity of the evidence, they are forced to adopt a more rigorous stance than many of their New World counterparts. To bring all interested parties together, a meeting was arranged by Commission 41 and cosponsored by IAU and IUHPS, on "Archaeoastronomy in the Old and New Worlds". It was held at Oxford, 4-9 September 1981, and attended by some eighty astronomers, archaeologists, historians and anthropologists, many of whom took the opportunity constructively to focus attention on the shortcomings of workers in other disciplines. Other meetings attended by historians of astronomy included a symposium on Christiaan Huygens held in Amsterdam, 22-25 August 1979; a celebration in honour of Aristarchus of Samos held in Samos, 18-20 June 1980; a conference on astronomy in the Middle Ages held in Aarhus, 20-21 November 1980; and the sessions on history of the physical sciences at the XVlth International Congress of the History of Science held in Bucharest, 26 August - 3 September 1981. The bibliography of articles and books in history of astronomy is edited annually by P.G. Kulikovsky on behalf of the Astronomical Council of the USSR Academy of Sciences and under the auspices of Commission 41, and this is distributed privately to over two hundred addresses, including all members of the Commission. Other bibliographical sources of value include the annual critical bibliography published in the history of science journal Isis, and the relevant sections of A & A Abstracts. It is invidious to single out for special mention individual books and articles, and this is especially so when so much effort is being invested in writing for GHA. It is however pleasing to note two books on the history of recent astronomy: the substantial Source Book in Astronomy and Astrophysics, edited by K.R. Lang and O. Gingerich, and The Expanding Universe: Astronomy's Great Debate 1900-1931, by R.W. Smith. M.A. HOSKIN President of the Commission

42.

CLOSE BINARY STARS (ETOILES DOUBLES SERREES)

PRESIDENT: B. Warner VICE-PRESIDENT: A.H. Batten ORGANIZING COMMITTEE: A.M. Cherepashchuk, M.G. Fracastoro, K. Gyldenkerne, M. Kitamura, R.H. Koch, Y. Kondo, G. Larsson-Leander, L.B. Lucy, S.D. Sinvhal, J. Smak, E.P.J. van den Heuvel, J.A.J. Whelan 1. Introduction Interest in close binary stars continues to grow apace. Substantial fractions of the observing time on the International Ultraviolet Explorer and the various xray satellites have been devoted to extending our knowledge of a variety of interacting binaries. These, together with applications of novel ground-based techniques and the steady improvement of traditional methods, and developments in methods of analysis, have led to major advances in understanding of the properties and evolution of close binary stars. Our Symposium Close Binary Stars held in Toronto, 7-10 August 1979, was attended by 170 participants from 26 countries and over 100 papers were presented. The proceedings have been published as IAU Symposium No. 88, Close Binary Stars: Observations and Interpretation, eds. M. Plavec, D.M. Popper and R.K. Ulrich; Reidel Publishing Co., 1980. Commission 42 is sponsoring a meeting, IAU Colloquium No. 72, Cataclysmic VariThis is co-sponsored by Commissions 27, 35 and 48.

ables and Related Objects, to be held in Israel 9-13 August 1982.

Meetings which have been co-sponsored by Commission 42 are IAU Symposium No.

93, Fundamental Problems in the Theory of Stellar Evolution, held in Kyoto, Japan, 22-25 July, 1980; IAU Colloquium No. 69, Binary and Multiple Stars as Tracers of Stellar Evolution, held in Bamberg, Germany, 31 August-3 September, 1981; IAU Colloquium No. 70, The Nature of Symbiotic Stars, held at Haute Provence, France, 26-28 August, 1981; IAU Colloquium No. 71, Activity in Red-spotted Stars, held at Catania, Italy, 10-13 August, 1981; and IAU Symposium No. 99, r,./olf-Rayet Stars: Observations, Physics and Evolution, held in Cozumel, Mexico, 16-22 September, 1981. Other Meetings, the published proceedings of which will have interest to Commission members, are Photometric and Spectroscopic Binary Systems (eds. E.B. Carling, and Z. Kopal, Reidel, Dordrecht, 1981); IAU Colloquium No. 53, rv17ite Dwarfs and Variable Degenerate Stars, held at Rochester, USA, 31 July-3 August, 1979; IAU Colloquium No. 59, Effects of Mass Loss on Stellar Evolution, held in Trieste, Italy, 15-19 September, 1980; and the IAU Regional Meetings Variability in Stars and Galaxies, held in Liege, Belgium, 28 July-l August, 1980 and the 2nd AsianPacific Regional Meeting held in Bandung, Java, 24-29 August, 1981. Workshops on cataclysmic variable stars were held in Rochester, USA, on 3 August, 1979; in Austin, USA on 24-26 March, 1980; and in Santa Cruz, USA, 12-31 July, 1981. No proceedings were published from these meetings. Other proceedings published in the period 1979-81 include Sistemas Binarios Cerrados (Colloquium on close binary stars held at Sao Paulo, February 1977), ed. R.V. de Moraes, Inst. Astr. et Geofis., Sao Paulo; Close Binaries and Stellar Activity (Joint Commission Meeting at the 1979 Montreal IAU General Assembly), Highlights of Astronomy, Vol. 5, Reidel; The Cataclysmic Variables and Related Stars 553

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(meeting held at Kyoto University, 24-25 February, 1981), published (in Japanese) by Kyoto University. Observers were greatly assisted by the publication in 1979 of the 5th edition of A Finding List for Observers of Interacting Binary Stars, by F.B. Wood, J.P. Oliver, D.R. Florkowski and R.H. Koch (University of Pennsylvania Press). From this list, the authors have selected a number of objects that appear particularly in need of further observation (IBVS No. 1708). Z. Kopal's monograph, Language of the Stars: a discourse on the theory of eclipsing variables, was published as Vol. 77 of the Astrophysics and Space Science Library (Reidel). The Bibliography and Program Notes on Close Binaries continued to be issued from Lund Observatory, edited by G. Larsson-Leander. Nos. 32-35 appeared during the triennium. The regional contributors were K.D. Abhyankar (India and Indonesia), B. Cester (Italy), D.S. Hall and G.W. Henry (USA, except the west coast), M. Kitamura (Japan, China and Korea), H. Mauder (Germany and the IAU Circulars), C.D. Scarfe (Canada, USA west coast, Mexico), A. Schulberg (USSR), R.F. Sistero (Southern Hemisphere), F. van't Veer (Western Europe), and M. Vete~nik (Central and Eastern Europe, except Germany and USSR). This Report has been compiled principally from sections written by members of the Organizing Committee, and is based on published literature and information contributed by members of the Commission. In addition, Drs. D.M. Gibson and R.W. Hilditch kindly provided the sections on Radio Observations and Algols respectively. Because of limitations of space, not all the information received has been incorporated in the Report. Key to the references:

AA = Acta Astron. AAp = Astron. Astrophys. AAp Sup = Astron. Astrophys. Suppl. Ser. AA Sin = Acta Astron. Sinica AJ = Astron. J. AN = Astron. Nachr. Ann Rev AAp = Ann. Rev. Astron. Astrophys. Ann Tokyo = Ann. Tokyo Astron. Obs., Second Ser. ApJ = Astrophys. J. ApJ Sup = Astrophys. J. Suppl. Ser. ApL = Astrophys. Lett. ApSpSc = Astrophys. Space Sci. ATs = Astron. Tsirk. AZh = Astron. Zh. Akad. Nauk USSR BAAS = Bull. American Astron. Soc. BAC = Bull. Astron. Inst. Czechoslovakia BASI = Bull. Astron. Soc. India

IAUC = IAU Circ. IBVS = Inf. Bull. Variable Stars Izv Krym = Izv. Krymskoj Astrofiz. Obs. JRASC = J.R. Astron. Soc. Canada MittAG = Mitt. Astron. Ges. MN = Mon. Not. R. astr. Soc. MSAI = Mem. Soc. Astron. Italiana obs = Observatory PASJ = Publ. Astron. Soc. Japan PASP = Publ. Astron. Soc. Pacific PerZv = Perem. ZVezdy, Byull. pis AZh = Pis'ma v Astron. Zh. Publ DAO = Publ. Dominion Astrophys. Obs. Publ Tartu = Publ. Tartu Astrofiz. Obs. S&T = Sky and Telescope Trudy Kazan = Trudy Kazan. Gorod. Astron. Obs.

2. Observational Techniques Close binaries continue to be observed by almost every available technique. Details of spectrographic, photometric, polarimetric, X-ray and radio observations may be found in later Sections. In spectrography, the introduction of digital electronic methods (e.g. Reticons, Digicons) has led to tremendous improvements in sensitivity, signal-to-noise and consequent time resolution, particularly in the area of cataclysmic variables (Stover et al., ApJ 240,597; Young et al., ApJ 244,259). The extended red response of these digital spectrographs has resulted in the detection of the red companions in a number of objects (Stauffer et al., PASP 91,59; Hade, A;:oJ 246,215 and AJ 84,

CLOSE BINARY STARS

555

562; Young and Schneider, ApJ 247,960). At very high resolution, digital coude spectra have been obtained of U Cep (Lambert & Tomkin, MN 186,391) and infrared Fourier Transform spectra have shown CO emission in Nova NQ Vul (Ferland et al.,

ApJ 227,489).

High time resolution photometry continues to be extensively applied (see Section 6D). A novel application by Hildebrand et al. (ApJ 248,268) determined the colours of the fast oscillations in AH Her. The first application of DDO photometry to W UMa systems was made by Hilditch (MN 196,305). An extensive search for polarization in cataclysmic variables has been made by Stockman et al. (ApJ in press). Spectropolarimetry of AMHer (Schmidt et al., ApJ 243,L157) led to detection of Zeeman splitting in the Balmer absorption lines. A review of ultraviolet observations of close binaries from space has been given by Kondo (Highlights 5,849). Ultraviolet photometry from DAD 2, including, e.g. AG Peg, was reported by Gallagher et al. (ApJ 229,994). Extensive use of IUE has been made, the details of which are given in Section 6B. X-ray satellite observations (see Section 4D) led to the detection of X-rays from RS CVn stars (Walter et al., SAO Special Rept. No. 389). An X-ray survey was made for cataclysmic variables (Becker and Marshall, ApJ 244,L93) and several more are in press. 33-sec X-ray pulsations were detected in AE Aqr (Patterson et al., 240, L133). Co-ordinated optical, UV and X-ray observations were carried out by Fabbiano

et al. (ApJ 24.3,911), Hutchings (PASP 92,458), Szkody et al. (ApJ 246,223) and Szkody (ApJ 247,577).

Speckle interferometry of Algol was obtained by McAlister and De Gioia (ApJ 228,493) and Bonneau (AAp 80,Lll). VLBI and VLA radio observations (Section 4E) include the detection of triple structure in an X-ray burster (Hjellming & Eurald, ApJ 246,L137) and Sco X-I (Geldzahler et al., AJ 86,1036) and jets in SS 433 (Section 4E). 3. Methods of Analyzing Light Curves (G. Larsson-Leander) During the past triennium, the methods of analyzing light changes in the frequency domain were pursued vigorously, primarily by Kopal and his present and previous collaborators. A very brief description of the methods was attempted in the 1979 Report, mainly based on the then pub lished papers in the series "Fourier Analysis of the Light Curves of Eclipsing Variables" (ApSpSc). A full descriotion of the methods developed by Kopal and his school is now available in Kopal's monograph The Language of the Stars (D. Reidel, Dordrecht, 1979). Further papers have also been published in the series m8ntioned above. Alkan (ApSpSc 58,453) presented another method to evaluate the a~-functions numerically, Demircan CApSpSc 59,313) deduced neloi' properties of the aQ" and the moments A and developed an iterative method to solve the fundamental ec1i~se parameters a anamc o in terms of observed quantities. The so-called g-functions, which have a and Co as arguments, were discussed by Edalati CApSpSc 59,333) from a theoretical point of view, and he gave in another paper (ApSpSc 59,443) numerical results pertaining to the determinacy of solution for the geometrical elements. Photometric perturbations from distortions due to axial rotation and tidal action were considered by Alkan and Edalati (ApSpSc 59,431), and the error analysis was treated by Kopal CApSpSc 66,91). In the latest paper of the series (No. XXVI), Kopal and Yamasaki (ApSpSc 72,3) gave analytical expressions for the incomplete Fourier transforms underlying Kitamura's 1965 method. The numerical coefficients, tabulated by Kitamura 1967, were checked and found of high quality.

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In another series of papers, Demircan (ApSpSc 61,499,507,62,189,235,67,367,375, 72,281,287) suggested modifications to the Kopal procedure and discussed various alternative series developments of the loss of light (l-l) in terms of the elements. In addition to Kopal' s integral transform A2 ' generalizations were made by introducing either an exponential or a Jacobi poly~omial as multiplicative factor into the integrand. Other integral transforms were also used. As pointed out by Demircan, principally the same solution should be obtained by using any of the transforms, but in practice this may not be so, because the geometric determinacy of the elements will be different in different transforms. In the opening paper of still another series, "Linear Analysis of the Light Curves of Eclipsing Variables", Kopal and Sharaf (ApSpSc 70,77) considered model analysis for the fractional loss of light in the sense of the least-squares criterion. Other contributions to the Fourier techniques include a study by Rovithislivaniou (Jj.pSpSc 59,463) of the photometric perturbations for partial eclipses and a generalization by Niarchos (ApSpSc 76,503) of the Kopal method to evaluate the proximity effects. Smith and Theokas (ApSpSc 70,103) developed a method to solve for atmospheric eclipses, using either the A 2m or the A2m-moments, previously introduced by Smith. The Fourier techniques were applied to many eclipsing systems, and in most cases the papers have been published in ApSpSc. These methods also dominated the NATO Advanced Study Institute at Maratea, Italy, in June 1980, the proceedings of which were printed as Photometric and Spectroscopic Binary Systems (see Introduction). This book contains, i.a., an extensive discussion by Jurkevich et al. of the error analysis of the elements, and papers by Demircan, Zafiropoulos, Rovithis-Livaniou, and Niarchos on various topics of the theory. A computer program for the frequencydomain analysis is presented by Gimenez and Garcfa-Pelayo. The well established synthesis methods for analyzing light curves were used extensively by many groups. It appears that D.B. Wood's code WINK and the WilsonDevinney (WD) code hold their positions as most popular among the users. Wilson (ApJ 234,1054) generalized the WD code to include eccentric orbits and non-synchronous rotation. Semi-detached, detached, double-contact, and X-ray binaries can now be modelled for arbitrary rotation and orbital eccentricity. For contact binaries the models are restricted to the synchronous, circular-orbit case. It is possible to obtain the differential corrections solutions to the light and radial-velocity curves simultaneously. Hill (Publ DAO 15,297) described his computer program (LIGHT), which is based on Roche geometry and is suitable for contact and under-contact systems, although over-contact systems can be handled approximately. Passbands, simulating instrumental response functions, can be synthesized by convolving given response functions with light curves calculated at up to 30 wavelengths. A relatively simple code was developed by Napier (MN 194,149), ado?ting the ellipsoid-ellipsoid model and treating the reflection effect semi-analytically. Etzel, in the Carling-Kopal book mentioned above, described a fast and flexible method (EBOP) for treating well-detached systems. It has been used with success by Etzel and Popper. When compared with WINK, it is more accurate for spherical stars and 15-40 times faster. 4. Observational Data A.

PHOTOMETRIC OBSERVATIONS AND SOLUTIONS (R.H. Koch) This section was compiled from materials held at the University of Pennsylvania by June 30, 1981 and is intended to provide continuity with the 1979 version preoared by T. Herczeg. The earlier version occupied about 2.5 pages with most of its-

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content in Tables 1 and 2 Photoelectric Observations and Photometric Solutions, respectively. Photoelectric observing has increased dramatically in the last triennium as may be seen from the first two entries of the present Table 1, which refers to spacecraft UV through L-band radiometry and conforms to Herczeg's precept of citing references which contain a "considerable amount" of new data. No increase of space has been .allocated for the 1982 report and thus a presentation analogous to Herczeg's Table 1 is impossible. (Such a table has actually been compiled in manuscript form and could be made available upon request. However, it is my belief that, had the pressure of space not even existed, the broad distribution and acceptability of The Bibliography and Program Notes on Close Binaries make the familiar Table 1 an anachronism). It is worthwhile to examine the photoelectric effort in order to see some effects of so much work. The first and third entries of Table 1 show that ~100 binaries observed from 1975 to 1978 were re-observed in the following 3 years. This is Table 1.

Photoelectric Observing Programs for the Past Two Triennia

Close binaries observed References for photoelectric data Binaries not observed 1975-1978 Northern systems (0) +23 0 ) Equatorial systems Southern systems (0) -23 0 )

1975-1978 209 346 88 50 35

1978-1981 342 564 240 120 77

76

a healthy statistic for a large number of objects show time-dependent behaviour that is not phase-locked to the Keplerian period, and the accumulation of such photometric history continues to be an important function of the Commission. Even more impressive, however, are the 240 binaries studied again after an interval of at least 3 years or studied for the first time. There can be no doubt that interesting and extreme objects are now accessible to the larger, better-sited telescopes eauipped with modern detectors and improved data handling procedures. Efforts to move toward ever-fainter binaries will be rewarding. The last 3 entries of Table 1 show that the increase of observing effort has been achieved in an absolute sense allover the sky, and that there has been a substantial relative gain in coverage of the southern constellations. A few new, archival photographic light curves are likely to be enduringly important: KR Aur AJ 85, 1092; V1329 Cyg IBVS 1525; V1357 Cyg BAC 30,250; V3885 Sgr PASP 90,216; NJL5 IBVS 1527; and A0538-66 Nat 288,147. There appears still to be a need for a summary of photometric solutions and this appears in the following Table 2 listing citations for essentially non-dimensional analyses or syntheses of light curves. In the present usage, "non-dimensional" implies that investigations of light curves founded primarily upon scaled (e.g., in c.g.s. units or in solar units) are not included in the table. Since 1978 the number of light curve studies has not increased so much in a relative sense as has the number of photoelectric data sets. Nonetheless, there has been a 25% increase in the number of light curve solutions in just these 3 years. This is due primarily to the increasing number of groups studying new and historical light curves by computerized methods. It is instructive to see in Table 3 the use that has been made of the assortment of computational procedures now available. The percentages in the table have been rounded to +1% and methods with a utilization smaller than 2% have been collected in the Miscellaneous category. In characterizing these procedures by so few authors some omissions of significant contributions by

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Table 2.

Photometric Solutions

RT And AApSup 36,415, ApSpSc 66,475; TW And AApSup 39,265; AB And ApSpSc 58,301; ST Aqr IBVS 1790; KO Aq1 PASJ 31,271, IBVS 1916; 00 Aq1 ApSpSc 58,301; QY Aq1 ApSpSc 76,111; V805 Aq1 AJ 86,102; RH Ara AApSup 29,273; V535 Ara ApSpSc 58,301, AApSup 36,287; V539 Ara AApSup 36,45, 39,255, RX Ari AApSup 42,195; SX Aur ApSpSc 63,351, ApJ 228,828, BF Aur AJ 84,236, EO Aur ApSpSc 70,461, 1M Aur AApSup 40,57; IU Aur AApSup 37,513; LY Aur AA 28,195; SU Boo AApSup 40,59. TY Boo ApSpSc 58.301; TZ Boo AApSup 33,63, MittAG 45,49; VW Boo ApSpSc 58,301, XY Boo ApSpSc 58,301; Y Cam AAPSup 39,265; SS Cam AA 29,243; SV Cam MN 187,797; SZ Cam AAp 86,264, BAC 31,321, ApSpSc 76,23; TU Cam AApSup 42,15; AS Cam ApSpSc 59,3, AApSup 39,255; AY Cam IBVS 1613; TX Cnc ApSpSc 77,75; WY Cnc ApSpSc 63,479; Ali Cnc MN 186,729; RS CVn ApJ 227,907; R CMa AApSup 36,273; CW CMa AApSup 42,15; FZ CMa AAp 94,201, YY CHi AAp 94,391; OY Car AAp 85,362, 94,L29; QZ Car ApJ 231,742; RX Cas Publ Tartu 58,3; TV Cas Trudy Kasan 42-43,72, AApSup 39,273; TW Cas AApSup 39,235, YZ Cas AApSup 42,15; AB Cas ApSpSc 71,249; CW Cas ApSpSc 58,301; HT Cas BAAS 11,664, ox Cas ATs 1033, AAp 82, 386; PV Cas ApSpSc 75,455; V523 Cas Trudy Kasan 42-43,46, AJ 86,98, RR Cen ApSpSc 58,301, U Cep MN 187,699, AApSup 40,135; VV Cep Ann Tokyo 17,147, PASJ 32,163; VW Cep ApSpSc 58,301, IBVS 1686; XY Cep ApSpSc 66,143; EK Cep Trudy Kasan 44,96, AApSup 42,15; NY Cep JRASC 73,258; TV Cet AAp 72,356, TY Cet AJ 86,102; XX Cet AApSup 39, 235; XY Cet ApSpSc 56,293, 71,385; Z Cha AA 29,309, RS Cha AAp 83,339, 85,259, RZ Cha AAp 85,259; RZ Com ApSpSc 58,301, CC Com ApSpSc 58,301; RH CrA BAC 31,297, TZ CrA AApSup 42,195; RH CrB AApSup 40,57; 42,195; H CrV ApJ 231,502; AI Cru ApSpSc 71,411, 77,197; 32 Cyg PASP 91,343; Y Cyg AApSup 39,255; SH Cyg AApSup 39,265, UZ Cyg AA 29,259; VW Cyg AA 29,259, AApSup 39,273; WH Cyg AApSup 39,265; CG Cyg ApSpSc 67,11; DK Cyg ApSpSc 58,301; KR Cyg AApSup 42,195; MY Cyg AApSup 39,255, AJ 86,102; V380 Cyg ApSpSc 71,385; V382 Cyg BAAS 11,439; V388 Cyg ApSpSc 76,111; V444 Cyg AZh 57,1033, V477 Cyg ApSpSc 59,3; V478 Cyg AJ 86, 102; V548 Cyg AApSup 39,235, ApSpSc 77,391, v729 Cyg ApJ 224,565; V1073 Cyg ApSpSc 58,301; Vl143 Cyg ApSpSc 59,3; AJ 86, 102, V1341 Cyg ApJ 231,539; AA 30,143; V1357 Cyg ApJ 226,264, 229,296, ATs 1095, W Del AApSup 39,273; RZ Dra AASin 21,158; TW Dra ApSpSc 73,389; HH Dra AApSup 39, 273; AI Dra ApSpSc 39,265; AR Dra AApSup 37,487; BS Dra AApSup 36,65, IBVS 1794. AJ 86,102, S Equ AApSup 36,273; RU Eri ApSpSc 74,41; UX Eri ApSpSc 58,301 WX Eri ApSpSc 65,443; YY Eri ApSpSc 58,301; CD Eri ApSpSc 67,213; CW Eri AApSup 42,15; U Gem AA 30,127; RH Gem AApSup 36,273; AL Gem AApSup 36,273; u Her AA 28,601, AAp 81,17, RX Her AApSup 42,285; UX Her AApSup 40,57; AD Her AAp Sup 39, 235; AK Her ApSpSc 58,301, PASP 91,234; ApJ 231,502; AM Her AAp 70,327; ApJ 230,502, MN 194,187; DI Her ATs 1016; DQ Her AZh 57,749; AA 30,267, ApJ 241,247; HS Her ApSpSc 76,111; LT Her AAp 79,354; V338 Her AApSup 39,273; V624 Her AApSup 39,255; AV Hya BASI 7,119, ApSpSc 76,173; EU Hya BASI 7,119; HS Hya AAP 85,259; 16 Lac IBVS 1552, RT Lac ApJ 227,907, SW Lac ApSpSc 58,301; CO Lac AApSup 42,15; EM Lac ApSpSc 58,301; Y Leo IBVS 1786; UZ Leo ApSpSc 58,301, Am Leo ApSpSc 58,301; AP Leo IBVS 1688; T LHi AApSup 36,273; 6 Lib AApSup 37,513; SW Lyn IBVS 1801, FL Lyr PerZv 20,588, AApSup 39,235; TY Men AJ 85,1098; TZ Men AAp 94,204; RW Man AApSup 39,273; VV Man AApSup 35,291; AO Man AApSup 39,255, TU Mus ApSpSc 76,23; UZ Oct AApSup 38,171; MittAG 50, 30; RV Oph AApSup 39,273; V451 Oph AApSup 39,255; V502 Oph ApSpSc 58,301; V566 Oph ApSpSc 58,301; V839 Oph ApSpSc 58,301; VV Ori ApSpSc 72,369, ER Ori ApSpSc 58,301; MW Pav AJ 85,1098, U Peg ApSpSc 58,301; AQ Peg AA 29,259; BB Peg AApSup 40,85; BK Peg AJ 86,102; DI Peg AAp 91,254, AApSup 42,195; EE Peg AApSup 42,15, b Per AA 29, 225; 6 Per ApSpSc 60,441, AAp 89,100; RT Per ApSpSc 58,3, 59,443, BASI 7,118, ApSpSc 75,329; ST Per AApSup 39,273; AG Per ApSpSc 57,17, IQ Per AApSup 42,15; IW Per ApSpSc 68,355; IZ Per Trudy Kasan 44,96, AApSup 40,57; AD Phe MittAG 45,49; AE Phe ApSpSc 58,301, 0 Pic ApSpSc 76,23, Y Psc AApSup 39,265, SZ Psc ApJ 227,907, UZ Psc ApSpSc 63,319; RW PsA ApJ 231,502; V Pup AJ 84,236; XZ Pup AApSup 39,265; UU Sge ApSpSc 73, 83; HZ Sge MN 184,835; AAp 76,168, AA 29,325; XZ Sgr AApSup 36,273,38,161, IBVS 1827; V505 Sgr AApSup 39,273, WI Sco AJ 84,236; V499 Sco ApSpSc 76,23; RT ScI BAAS 12,748; RW Tau AApSup 40,57; RZ Tau ApSpSc 58,301; CD Tau AApSup 40,145; HU Tau IBVS 1740, V471 Tau ApSpSc 57,219, AJ 86,572; HO Tel BAC 31,297; X Tri 39,265; W UHa ApSpSc 58,301; ApJ 239,919; UX UMa ApJ 241,247; VV UNa AApSup 40,57; XY UMa

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559

IAU Symp 88,423; AW UMa AJ 85,50, IBVS 1802; W UMi AApSup 40,57; S Vel IBVS 1634, 36,273; AH Vir ApSpSc 58,301; BH Vir AApSup 39,255, 42,195; BE Vul AApSup 40, 57; BS Vul AApSup 35,63; ER Vul AApSup 43,85; HR 5110 AJ 85,1082; HR9049 ApSpSc 74, 83; CPD-60 0 389 AA 30,113; HD5980 ATs 1047, HD152667 AAp 70,L49; w Cen V78 ApSpSc 64, 427; HDE269696 MN 183,523; AA 30,113; LB3459 MN 187,1; AA 30,113, Cen X-3 ApJ 226, 264; 4U1223-62 ApJ 226,264; 4U1626-67 ApJ 226,264; SS443 MN 194,293; LMC X-4 ApJ 226, 264; SMC X-I ApJ 226,264. Table 3. Percentages of Light Curves Studied by Different Computational Methods 1978-1981 Hill Horak Kitamura Kopal Miscellaneous Nelson-Davis Etzel Russell-Merrill Wilson-Devinney Wood

2% 2%

4% 17%

15% 2%

11% 14% 34%

unnamed workers have been inevitable. It is apparently a common experience that the speed of the Russell-Merrill x-functions offers a convenient and useful initialization of parameters for other codes if the eclipses are sufficiently geometrically deep. The wealth of these different procedures now offers opportunity to scrutinize the strengths and defects of each procedure in order to determine its limits and, if possible and necessary, to ramify the physical model to which each procedure is applied. Comparative studies of specific light curves by different procedures appear rather commonly among the citations in Table 2. One of the most heartening developments is the ingenuity underpinning many ad hoc procedures collected above as Miscellaneous ones. For the most part, these have been applied to atmospherically-eclipsing systems, cataclysmic variables, and spotted star systems and have required parameterization beyond the conventionally interacting two-body system. B.

SPECTROSCOPIC AND SPECTROPHOTOMETRIC INVESTIGATIONS (A.H. Batten) Table 4 is a list of references to spectroscopic and spectrophotometric studies of binary systems, made in the triennium under review. It has not been possible to observe exactly the prescribed limits for the review period. References to IAU Circulars have not been given, and references to published abstracts have been dropped when it could be clearly ascertained that the full paper has been subsequently published. An asterisk following a reference indicates that an orbital study is to be found in it. Spectroscopic studies of optical counterparts of X-ray sources have been included in the Table, but no attempt has been made in this section to provide complete references to such objects. The growing need for some standard nomenclature for faint objects is very apparent in the Table. Research in this field continues at a very high level of act~v~ty. Our knowledge of late-type, long-period (and mostly single-spectrum) sys.tems has been vastly increased by the application of radial-velocity spectrometers, particularly but not exclusively, by Griffin himself. New statistical studies of these systems will soon be needed. The application of the objective-prism to the study of binary stars has been revived and modified by Gieseking. To save space, by avoiding frequent reiteration of the same reference, his important paper in AApSup 43,33 has not been included in Table 4. The orbital studies of 27 spectroscopic binaries contained in it should not, however, be overlooked. Systems containing Wolf-Rayet stars have continued to attract interest. Conti, Massey and Niemela, on the one hand, and Moffat and Seggewiss, on the other, have studied several. Massey's work has led to an important summary of information on

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the masses of these objects (ApJ 246,153). Evidence is mounting that not all WolfRayet stars are members of close binary systems. Studies in the far ultraviolet have been increasingly made in the past few years. Two sources of important papers that did not come to hand soon enough to be fully incorporated into Table 4 are: ESA SP 157 (Proceedings of ~he 2nd European IUE Conference) and NASA Conference Publica~ions 2171 (The First Two Years of IUE). Additional important papers on several systems will be found in these two volumes. Plavec and his associates report conside.rable progress in their ultraviolet studies of Algol-type systems. They have also studied the "Serpentid" group (named after an early example, W Ser). Far UV spectra of this latter group are characterized by strong emission lines of ionized heavy elements. Systems whose visible spectra are as diverse as those of 8 Lyr, SX Cas and W Ser, appear to have closely similar UV spectra. On the other hand, the UV spectra of Algol-type systems tend to agree with the spectral types assigned to the visible spectra except that sometimes strong absorption lines of higher excitation than expected are seen. Plavec and Keyes also find strong evidence for the binary nature of many symbiotic stars. The RS CVn group continues to attract attention and this is especially reflected in the prominence of V7ll Tau (HR 1099) in Table 4. The Table also reflects the excitement generated by SS 433, although detailed discussion of that object is out of place in this section. At the opposite extreme we might point to the spectroscopic studies of selected visual binaries by Batten, Feke1, Scarfe and West. Table 4 Z And IBVS 1636, MSAI 50,221, IAU Symp 88,543; AN And Izv Krym 59,143- EG And ApJ 237,831, Nature 284,148; ET And IBVS 1600*,1657, a And AApSup 43,209, A And ApJ 227, 870, s And PASP 92,825*; R Aqr ApJ 237,506,840, Na~ure 284,148; AE Aqr ApJ 234,978, MN 191,559; U Aql PASP 91,840, V603 Aql ApJ 234,978; V805 Aq1 ApJ 244,541*, V822 Aql PASP 93,318, n Aq1 ApJ 238,L87; TT Ari BAAS 12,855; UX Ari ApJ 239,911, 241,759, AJ 85,1086, T Aur MN 192,127*, AR Aur PASJ 31,821; a Aur ApJ 241,279; E Aur AAp 69,23, 76,365, MSAI 50,201; s Aur PASP 92,790, BAAS, 12,851, Na~ure 286,580; TZ Boo MittAG 45,49; 44i Boo BAAS 11,722, Z Cam IAU Coll 53,499, ApJ 236,839; SZ Cam BAC 31,321, SY Cnc Pis AZh 5,452; WY Cnc IBVS 1484; Y Cnc pis Azh 5,452, AH Cnc MN 186,729*, 45 Cnc AJ 86,271*, RSCVn PASP 92,675; TX CVn AAp 88,141*; UW CMa MittAG 45,52, IAU Symp 88,195, IBVS 1762, EZ CMa ApJ 239,607, a CMa ApJ 232,L189; YZ CMi BAAS 11,629, 12,500,527,ApJ 231,L77, 8 Cap ApJ 228,497*, s Cap ApJ 239,L79, OY Car AAp 85,362*, MN 194, 17P*, QZ Car ApJ 231,742*,239,L79, 9 Car PASP 91,442*, RX Cas and SX Cas BAAS 13,523; RZ Cas AApSup 38,155*; HT Cas AAp 76,365, ApJ 245,1035*; BV Cen IAU Colloq 53,145, ApJ 235,945*; V346 Cen PASP 90,728*; V436 Cen MittAG, 50,28; U Cep ApJ 233, 906, 244,546*, MN 186,391, MittAG 45,177, IAU Symp 88,237; VV Cep BAAS 10,620, MSAI 50,207, IAU Symp 88,549, PASJap 33,177; CQ Cep IAU Symp 88,177*, CX Cep ApJ 244,169*, UV Cet BAAS 11,629; Z Cha MittAG 45,158, Obs 99,186; 26 Com JApA(Ind) 2,115*, L CrB MN 191,521*, U CrB Publ DAO 15,419*; BI Cru PASP 92,479; a 1 Cru MN 191,217*; SS Cyg ApJ 234,997, 235,163, 240,597*, AJ 84,655, IAU Colloq 53,489*, SW Cyg AA 29,653; CG Cyg AJ 84,1218; CH Cyg IAU Coll 53,459, PASJ 31,307*; ApJ 242,188, AAp 84,366, MSAI 50,207; CI CygIzvKrym 59,133, IBVS 1759,1945, AAp 93,1, Rap Int Frascati No. 19, V382 Cyg PASP 91,474; V389 Cyg MittAG 45,53; V444 Cyg Pis AZh 5,398, V1073 Cyg IBVS 1579, V1329 Cyg IBVS 1525*, BAC 30,308, ApSpSci 75,237; V1341 Cyg (=Cyg X2) ApJ 231,539*, BAAS 10,607, PASP 92,147*, V1357 Cyg (=Cyg Xl) AJ 83,962, ApJ, 226, 976, PASP 91,796; V1500 Cyg ApJ Sup 38,89, IAU Coll 53,522, ApJ 230,162, Publ DAO 15,73, PASP 91,446, ApJ 236,847,237,529; V1668 Cyg AAp 85,L4, Pis AZh 6,486; 31 and 32 Cyg IAU Symp 88,555; 47 Cyg AJ 86,271*; 57 Cyg MN 189,551*, 81 Cyg PASP 93,323; HR Del Nauch Inf No. 42,21, Pis AZh 5,537, PASP 91,661,92,458, ApJ 232,176*, BAC 30, 129, IBVS 1811, AA 29,681, ApSpSc 76,149; 0 Del BAAS 11,728; AG Dra MN 195,733, BY Dra ApJ 234,958*, 240,567, PASP 92,548; DE Dra MVS 8,105,40 Eri B AJ 85,1255, U Gem BAAS 11, 629, PASP 91,59, AJ 84,562, ApJ 246,215*, YY Gem PASJap 32,451; DN Gem IEVS 1711, IR Gem Pis AZh 5, 452, y Gem BAAS 10,631*, AM Her BAAS 10,607, ApJ 230,502,

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245,1043*, AZh 57,65, IAU Symp 88,467, PASP 93,71; DQ Her ApJ 224,171, 226,963, 232, 500*, 233,935, 238,955*, AA 30,267*; HZ Her (=Her Xl), IAU Symp 88,349, 88 Her BAC, 29,278, IBVS 1565, TW Hor AAp Sup 36,283*, RW Hya BAAS 11,730, Nature 284,148, ApJ 240,114, EX Hya IAU Coll 53,145, AAp 87,349*, VW Hyi IAU Coll 53,145, ApJ 234,1016, ESO Mess No. 16,15; WX Hyi ESO Mess No. 16,15; RT Lae BAAS, 11,651; AR Lae IBVS, 1880, AJ 85,1086, 86,766; EW Lae BAC 32,56; 14 Lae IBVS 1886; 16 Lae IBVS 1552; 93 Leo IBVS 1833; 19 LMi PASP 92,98*; MV Lyr ApJ 245,644*; B Lyr IBVS, 1535; ATs 1009, 1036, Izv Pulk No. 197,89, MSAI 50,203, IAU Symp 88,271, Pis AZh 6,171,587,628; T Man ApJ 249,1083, AU Man 16 Reunion Assoc. Arg. Astr.; V616 Man MN 192,709; U Oph ApJ Sup 41,1; RS Oph PASP 91,46; RZ Oph ApJ 226,937*, AA 31,25 1' ; UU Oph PASJ 32, 445; V1054 Oph BAAS 12,500; n Ori BAAS 12,452; ~ Ori B PASP 92,785*; 0 Ori E BAAS 10,683; RV Peg AJ 84,655; AG Peg IAU Symp 88,535; BAAS 11,731; AV Peg AJ 84,1598; EE Peg ApJ 244,541*; II Peg PASP 92,333, AJ 85,1086, y Peg IBVS 1598; X Per (=4U 0352 + 30) Ap J, 227,L21, IAU Symp 88,233,367, BAAS 12,500, Izv. Krym. 61,77; AAp 94,345; RY Per AZh 56,1012,1220; AG Per ApJ Sup 4.1,1; GK Per IBVS 1988, B Per AA 29,339,549; AJ 86,258; IAU Symp 88,223,225; ¢ Per ApJ 233,L73*, IAU Symp 88,199, PASP 93,297*, b Per AA 29,225*; AI Phe AAp Sup 36,453*, MittAG 45,49, RR Pie ApJ 228,482; 0 Pie PASP 92,688; SZ Pse AJ 85,1086, 86,771; 64 Pse AAp Sup 35,203*; RX Pup MN 187,813; VV Pup IAU Coll 53,330,334; Nature 281,47, Proc ASA 3,311, MN 191, 589; U Sge ApJ 231,495*; V Sge IAU Coll 53,448; WZ Sge IAU Coll 53,139,458,522, ApJ 234,182*, 236,854*,L29, 237,89*, MN 191,457, AAP 87,31, IAU Symp 88,447; FG Sge AJ 85,867; 0 Sge Proc 2 Eur IUE Cont p.229; V356 Sgr ApJ Sup 41,1; V3885 Sgr ApJ 234, 1016, ~ Sgr IBVS 1598, BAAS 12,869; 0 Sgr AAp 71,310, MSAI 50,203, IBVS 1598, IAU Symp 88,271; U Sea IBVS 1738, MN 195,61, V453 Sea MN 194,537; V701 Sea AAp 82,225 1' , V818 Sea (=Seo Xl) BAAS 10,607, ApJ 226,276, 237,596, V861 Sea BAAS 10, 608, ApJ, 230, 519*,231,171; B Sea A PASP 91,87*; BAS Ind 7,123, ~l Sea 16 Reunion Assoc Arg Astr; RY Set IBVS 1580, W Ser BAAS 10,609, UZ Ser ApJ 234,1016, CV Ser ApJ 245,195'~, RW Tau IAU Symp 88,233; V471 Tau IBVS 1860,1951, V711 Tau AJ 83,1469ff, 85,1086, ApJ 224,143, 239,L121, ApSpSc 74,87, PASP 91,431, IBVS 1669; 33 Tau JRASC 74,365; A Tau ApJ Sup 41,1, IAU Symp 88,293; RW Tri AA 29,469*; W UMa and AW UMa MN 195, 931*; XY UMa IAU Symp 88,423, Proc 2 Eur IUE Cont p.81; SU UMa Pis AZh 5,452; AN UMa BAAS 10,607, ApJ 240,871; 55 UMa MN 195,805*, yl Vel PASP 92,819*; y2 Vel ApJ 227, 884, 228,147, 238,244*, a Vir ApJ 227,884, 228,127; Nova Vul 1976 AJ 85,1232; Nova Vul 1979 IBVS 1835; HR913 Obs 100, 113*, HR 2024 AJ 86, 271*: HR 2072 AJ 85,858; HR 2081 PASP 91,824*; HR 2142 PASP 90,494, IAU Symp 88,293; HR 2923 PASP 92,713, HR 3337 BAAS 10,660; HR 3805 Obs 101,79*; HR 4249A Obs 100,161*; HR 4474 MN 193,957*; HR 4492 AJ 85,858; HR 4511 ApJ 245,201; HR 5161 PASP 91,521 1 25 keY) tail in the spectrum of Perseus cluster (Primini et al. 1981). A rich cluster of galaxies in Ophiucus, which is the optical counterpart of the bright X-ray source 4u 1708-23, was discovered (Johnsten et al. 1980, Wakamatsu and Malkan 1981). K. FUTURE EXPERIMENTS Following X-ray satellite missions have been approved and are under preparation ( see, Proceedings of the Uhuru Memorial Symposium, J. of Washington Academy of Sciences 1981 11 No2) a) EXOSAT, the first X-ray astronomy mission form the ESA, will be launched in 1982. The experiment payload consists of the medium energy detector array for observing faint sources and precise location by means of lunar occultation, the low energy imaging telescope with geometric area of 90 cm 2 and focal length 109 cm and the gas scintillation proportional counter. b) The Rosat mission, a German X-ray telescope, is due for launch before mid-1980s. The payload is a mirror telescope with a geometrical collection area of 1200 cm 2 and a focal length of 240 cm. In addition to the pointed observations the first X-nay sky survey with a imaging telescope is planned.

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c) Succeeding the Hakucho satellite, which continues to be in operation as of December 1981, the ASTRO-B and the ASTRO-C will be launched from Japan. The ASTRO-B will be launched in Feburuary 1983: One of its major instruments is a large area gas scintillation proportinal counter array with a total area of '" 1000 cm2 for the temporal-spectral study of sources. The ASTRO-C is for the high sensitivity observation of variable sources with a large area proportional counter array: it will be launched on 1986/87. The X-ray Timing Explorer, the Extreme Ultraviolet Explorer and the Advanced X-ray Astrophysics Facility (AXAF), all from NASA, are awaiting for approval. The AXAF is the advanced version of EINSTEIN, which is hoped to provide X-ray astronomy another break-through. References Vlarwick, R. S. et al.: 1981, MNRAS, in Press McHardy, I.M. et al.: 1981, MNRAS, in Press Boldt, E.: 1981, Proceedings of the Uhuru Symposium (1980) J. of Vlashington Academy of Sciences, 71, p. 24 Kondo, I. et al.: 1981, Space Sci. Inst., 5, p. 211 Oda, M. and Tanaka, Y.: 1981, Proc. Japan-Italy Symposium on Fundamental Physics, Tokyo, p. 137; ISAS RN 150 Giacconi, R. et al.: 1979, Astrophys. J., 230, p. 540 Nagase, F. et~ 1981a, Nature, 290, p. 572 Nagase, F. et al.: 1981b, Preprint--Rappaport, ~ al.: 1980, Astrophys. J., 235, p. 570 Truemper, J. et al.: 1978, Astrophys. J. Le~, 219, L 105 Gruber, D. et~ 1980, Astrophys. J. Lett., 24~L 127 'Alheaton, H.A. et al.: 1979, Nature, 282, p. 24-0-Lang, F.L. et al.: 1981, Astrophys. ~Lett., 246, L 21 Lewin, H.H.G. and Clark, G.VI.: 1979, Proc. Symposium on X-ray Astronomy p.3 1980 Annals N.Y. Acad. Sci., 336, p. 451 Lewin, VI.H.G. and Joss, P.C.: 1981-:-Spa~e Science Reviews, ~, P. 3 Hayakawa, S.: 1981, Space Science Reviews, in Press Oda, M.: 1981, Proc. Vlorkshop on Gamma Ray Transients, Aug 5-8 1981 La Jolla in Press (ISAS RN 158) Proc. International School of Plasma Physics in Press (ISAS RN 162) Joss, P.C.: 1978, Astrophys. J. Lett., 225, L 123 Inoue, H. et al.: 1980, Nature, 283, p. 358 Oda, lIi.: 1981, Astrophys. and Space Science Library, 87 (Proc. HEAD/AAS Meeting 1980), p. 61 Murakami, T. et al.: 1980, Publ:. Astron. Soc. Japan, 32, p. 543, also see Oda, M. 1981 Pedersen, H. et al.: 1981, Astrophys. J. Submitted Kemp, J. et al.: 1981, Astrophys. J. Lett., 244, L 73 Friedman, ~t al.: 1979, Nature, 278, p. 4311 Walter, F. et al.: 1978, Astrophys.~, 83, p. 1538 Griffiths, R. et al.: 1979, Astrophys. J. Lett., 232, L 27 Cordova, F. et al.: 1981, Astrophys. J., 245 p. 6~ Haisch et al~80, Astrophys. J. Lett.,242, L 99 Holt, S~al.: 1979, Astrophy, J. Lett.,:234, L 65 Swank, J.H. et al.: 1981, Astrophys. J., 24~p. 208 Vaiana, G. et al.: 1981, Astrophys. J., 2~ p. 163 Harnden, F.~ al.: 1979, Astrophys. J~ett., 234, L 51 Seward, F. et al.: 1979, Astrophys. J. Lett., 234~ 55 Fabian, A.C~al.: 1980, MNRAS, 193, p. 175 --Becker, R.H. et al.: 1979, Astrophys. J. Lett., 234, L 73 Pye, J. et al.: 1981, MNRAS, 194, p. 564 Becker, ~et al.: 1980, Astrophys. J. Lett., 240, L 33

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Becker, R.H. and Helfand, D.J.: 1981 Astrophys. J., Submitted Winkler, P.F. et al.: 1981, Astrophys. J., 245, p. 574 Nomoto, K. and Tsuruta, S.: 1981, Astrophys~. Lett., 250, L 243 Seward, F. et al.: 1980, Nature, 287, p. 806 Makishima, K. et al.: 1981, Proc. 15th ESLAB Symposium June 1981 Amsterdam, in Press Giacconi, R. and Tananbaum, H.: 1980, Science, 209, p. 865 Cash, W. et al.: 1980, Astrophys. J. Lett., 238~ 71 Van Speybroeck, L. et al.: 1979, Astrophys. ~Lett., 234, L 45 Seward, F.D. and Mitchell, M.: 1981, Astrophys. J., 24~p. 736 Long, K.S. et al.: 1981, Astrophys. J. Lett., 234, L~ Clark, G. et al.: 1979, Astrophys. J., 229, p.~ Kriss, G.A~al.: 1980, Astrophys, J.~42, p. 492 Hutter and ~1ufsen: 1981, Astrophys. J., Submitted Shreier, E. et al.: 1979, Astrophys. J. Lett., 234, L 39 Fabricant, D~al.: 1980, Astrophys. J. 241, ~552 Worrall, D. et~ 1981, Astrophys. J., 243, p. 53 Zamorami, G. et al.: 1981, Astrophys. J.,~5, p. 357 Giacconi, R. et al.: 1979, Astrophys. J. Lett., 234, L 1 Marshall, F. et al.: 1980, Astrophys. J., 235, p~ Fabian, A.: 1981, Proc. Tenth Texas Symposium, in Press McKee, J. et al.: 1980, Astrophys. J., 242, p. 843 Jones, C. et al.: 1979, Astrophys. J. Lett., 234, L 21 Bechtold, J. et al.: 1981, Astrophys. J., Submitted Forman, W. et~ 1979, Astrophys. J. Lett., 234, L 27 Forman, W. et al.: 1981, Astrophys. J. Lett., 243, L 133 Henry, J.P.~l.: 1981, Astrophys. J. Lett., 243, L 137 Mushotzky, R~t al.: 1981, Astrophys. J. Let~ 244, L 47 Primini, F.A. et~ 1981, Astrophys. J. Lett., 24~L 13 Johnston, M.D.~l.: 1981, Astrophys. J. 245, in Press Wakamatsu, K. and Malkan, M.A.: 1981, Publ. Astron. Soc. Japan, 33, p. 59

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5. Solar Space Research C. de

Jager

A. ANALYSIS OF DATA FROM SPACECRAFT LAUNCHED BEFORE 1979 I. OSO-8 The last spacecraft in NASA's Orbiting Solar Observatory programme OSO-8, was launched in June 1975 and has been operating until October 1978. It carried among other instruments a high resolution telescope and multichannel spectrometer built under the responsibility of the Laboratoire de Physique Stellaire et Planetaire in France. An extensive review of the results obtained with this instrument can be found in Bonnet (1981), from which we extract: the detection of chromospheric oscillations in La; the establishment of an active region model which represents correctly the profiles of Ca II H-K, Mg II h-k, H La and LS observations. Several quiet and active prominences have been observed with OSO-8. II. Intercosmos Solar spectroscopic data were analysed in a cooperative programme between the Moscow group (Institute for Spectroscopy, and the Lebedev Institute), and the Wroclaw Astronomical Observatory. The analysis concentrated on the study of high-resolution spectra in the range 0,175 - 0,19 nm. Models of the differential emission measure distribution were calculated for large flares observed in October-November 1970. The models show two maxima in the distribution of the differential emission measure : one in the range of 10 - 20 x 10 6 K and the second at temperatures of 30 - 100 x 10 6K. Results are published in Hudson (ed.; 1981). Intercosmos -16 high resolution spectra were studied in the region of Mg XI and Mg XII resonance lines. The electron density in the emitting regions was estimated from the intensity ratios of the resonance, intercombination and forbidden Mg XI lines. The density in the Mg XI emitting volume of a coronal active region appears to be higher when the region is hotter. Papers on this subject have been submitted to Solar Physics. III. Solar Wind Studies Solar particles and solar wind properties are being measured by instruments on board of Helios 1 and 2 (both are heliocentric with periapsis at 0,3 AU and apoapsis at 0.98 AU) and on board of the International Sun Earth Explorers (ISEE 1, 2 & 3). Based on these missions, publications have appeared on solar wind properties and solar particle acceleration and propagation in the corona. A recent selection can be found in the Proceedings of the 17th International ·Cosmic Ray Conference, Paris, July 1981. B. SATELLITES LAUNCHED DURING THE REPORT PERIOD I. The Solar Maximum Mission (SMM) The most important event in the reporting period was undoubtedly the launch and operation of the Solar Maximum Mission (launch date February 14, 1980). The spacecraft and its instrumentation are described in a series of papers in Solar Physics 65, 1980. The SMM contains the following scientific instruments. - Gamma-Ray Spectrometer (Forrest et al., 1980) - Hard X-ray Imaging Spectrometer (Van Beek et al., 1980)

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Soft X-ray Polychromator (Acton et al., 1980) UV spectrometer and Polarimeter (Woodgate et al., 1980) Coronagraph / Polarimeter (Macqueen et al., 1980) Solar Constant Monitoring Package (R.C. Wilson, 1980)

Unfortunately the attitude control system of the spacecraft broke down after only nine months of operation. Owing to the fact that the solar maximum of 1979-1980 was the second highest on record since 1610 a large amount of new data could be acquired. Preliminary results are published in Hudson (1981), pp 247-287. Results appeared also in a special volume of Astrophys.J.Letters 244, Ll13-189, 1981. Here, we briefly list the most important findings: the magnetic field strength above a sunspot in the transition region is about half that of the photospheric value; oscillations occur in the transition region above sunspots; impulsive flare bursts in (hard) X-rays coincide in time with those observed in ultraviolet lines as well as in microwaves; large outstreaming motions are found preceding the occurrence of flares; "footpoints" of flares observed in hard X-rays and microwaves may occur simultaneously (within one or two seconds) at separations as far as 105 km apart; the diffuse (soft) X-ray emitting area of flares appear after the (hard) kernels, are slightly hotter, and may derive their content of energetic electrons from the kernels, where they apparently originate. The discovery of X- and UV-line precursors to flares, and giant X-ray emitting loops after large flares is another new result of SMM. A further result is the discovery of a series of y-ray line emiss,ions during important flares, indicating high-energy acceleration processes. SMM also discovered a relation between variations in the solar "constant" and sunspot development. The elaboration of the SMM data will still take several years, and may yet reveal several discoveries, still hidden in the available material. II. Prognoz 8 This spacecraft, launched December 25, 1980, carries among other payloads a solar X-ray photometer developed by the Ondrejov Observatory. The photometer measures in six energy bands (2-4, 4-8, 10-20, 40-80, an 80-160 KeV) with a time resolution of 10 seconds. III. Hinotori Hinotori (ASTRO), the Japanese astronomy satellite launched by the Institute of Space and Aeronautical Science of the University of Tokyo, has been continuously operating since February 26, 1981 to perform extensive observations of solar flares in X-rays and y-rays. Hinotori carries five instruments; they are (1) hard X-ray imaging telescope in the energy range of 10-60 keV (SXT), (2) Bragg spectrometers for 1,7-2, 0 A (SOX), (3) soft X-ray spectrometer for 2-20 keV (FLM), (4) hard X-ray spectrometer for 17-340 keV(HXM), and (5) y-ray spectrometer for 240-7000 keV (SGR). All the instruments monitor the full sun. The hard X-ray image is obtained by the rotating modulation collimator technique; computer processings of the data give two-dimensional images with about 10" resolution. The SOX, consisting of two flat Si0 2 crystals and scintillation counters, makesouse of the spacecraft rotation for scanning two wavelength bands: 1,81-1, 90 A and 1,7-2,0 A every 6 to 10 seconds with a resolution of 0,2 rnA and 2 rnA, respectively. The SOX has the capability to detect line polarization. Observations by FLM, HXM and SGR cover the flare spectra in a wide spectral range from 2 keV to 7 MeV almost simultaneously; the temporal resolutions are 125ms(HXM), 2s(SGR), and 4s(SGR). The 2-20 keV region is measured by the gas scintillation proportional counter which is capable to resolve line emission from the continuum. The gamma-ray line emissions can also be resolved. The spacecraft has the capability to record the initial 20 minutes of each flare.

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The following preliminary results have been obtained. In the early operation, by July 31, 1981, Hinotori observed 261 flares including 13 X-class events. The SXT has observed many events in the energy band of 12-30 keV (efficiency peak above 20 keV); several large events have been analyzed to reveal very compact sources for these hard X-ray bursts. With the exception of a few events most have linear dimensions less than the FWHM(30") of the collimator triangular response. The SOX has obtained a large number of high resolution spectra which include emission lines from Fe XIX to Fe XXVI, Ka and KS (1,75A). The La and satellites of Fe XXVI have been well resolved; their ratios give the electron temperatures considerably higher (3-10 million degrees) than the electron temperatures derived from the Fe XXV pair. A steady increase of the mean temperature from about 15xl0 6K to 30xl0 6K has been found in the rising phase of the impulsive flares. In the differential emission measure derived from the line intensities for these events a pronounced peak of the emission measure has been found to appear above 20xl0 6K and shift progressively to higher temperatures and then return to the lower temperatures. This time behaviour is considered to represent the heating and cooling in the flare. Line broadening of about 250 kms- 1 has been seen before the increase of the temperature. In the initial phases of some flares blue enhanced line profiles and Doppler-shifted complex profiles have also been found. The soft X-ray spectra in the range of 2-10 keV obtained by the FLM have given evidence for gradual heating of the flare plasma in the rising phase of small flares; in these spectra the emission lines from the He-like and H-like ions of Ar, Ca, Ti, Fe and Ni appear and become enhanced successively in this order, along with the increase of the continuum slope. The y-ray spectrometer(SGR) has detected significant emissions of following lines (shown in MeV) at least in two events: 0,51(e++e-), 0,84(56Fe),1,37(24Mg), 1,64(14N or 20Ne), 2,22(D), 4,44 (12C), 6,14( 16 0). Unidentified emission has been seen at 1,0 MeV. In the limb event (April 27) the 2,2 MeV line was less intense by an order of magnitude than the 4,4 MeV line. This supports the photospheric origin of the 2,2 MeV line. The continuum spectra extending to 7MeV have been observed. The spectra tend to show a break near 1 MeV. C. OBSERVATIONS BY ROCKET- AND BALLOON PAYLOADS I. The Transition Region Camera (TRC) The TRC is a small (10 cm) Cassegrain rocket-borne telescope built by the Laboratoire de Physique Stellaire et Planetaire du C.N.R.S. It is equipped with a filter wheel and a film cassette. Sequences of images at various wavelengths can be obtained through the rotation of the filter wheel and for various exposure times. This instrument has been launched twice on a NASA Black Brant rocket on July 3, 1979 and September 23, 1980, jointly with other solar instruments built by the Lockheed Palo Alto Research Laboratory (LPARL). The TRC has provided the best solar pictures ever obtained so far from above the earth atmosphere. The pictures correspond to La 121,6 nm (Bonnet et aI, 1980) and to the temperature minimum continuum, 160 nm (Bonnet et aI, 1982). The La pictures show a large variety of chromospheric features, in particular, magnetic loops of varying sizes and extension both in the chromospheric network and in the corona. These loops appear either as emission (bright) or absorption (dark) features. Optically thin coronal loops have been used to infer the density and temperature of neutral hydrogen in the corona. Temperatures of around 10 5 degrees K and densities of 5.10 5 cm- 3 neutral hydrogen atoms have been found (Bonnet et Tsiropoula, 1982). By contrast, the U.V. continuum pictures display very sharp features of point like appearance (bright points), and circular surface wave patterns revealed here for the first time. The bright points have an excess brightness of 100 to 200 K over the average background. They seem to be located at the edges of granules.

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Two more flights of the TRC are scheduled in 1982. An enlarged version of this instrument is in preparation at L.P.S.P. and L.P.A.R.L •. It is intended to fly first on a rocket and possibly later onboard the Space Shuttle. II. The Rocket Launchings For the investigation of solar X-ray emission within the Intercosmos programme the "Vertical-8" and "V-9" rockets were launched on 26 September, 1979 and 28 August, 1981, respectively. The instrumentation was designed at the Lebedev Phusical Institute (USSR), the Space Research Center at Warszawa (Poland) and the Ondrejov Observatory (CSSR) and included wideband photometers for the region 0.4-1.5 nm, Bragg-spectrometers with flat and bent crystal spectrometers for the region 0,6-1,0 nm, pinhole cameras, and two grazing incidence mirror telescopes forthe band 0,5-1,5 nm (spatial resolution: ca. 20"). The apparatus mounted on a 2-axis pointing system, was installed in a special vehicle. At an altitude of 100 km at ascent this vehicle was separated from the rocket landed with a parachute system. The maximum altitude achieved was about 500 km; the pointing accuracy was about 10 arc sec. By these experimetns X-ray photographs of the Sun were obtained in the ranges 0,8-2,2 and 0,6-2,0 nm. Simulaneously, high-resolution spectra around lines of Si XIV, XIII; A1XII; ;gXII, XI were obtined by the traditional scanning method. The fluxes in the same lines were also measured continuously, with a time resolution of about 0,04 s. The results were investigated with a view to obtain the distribution of temperature and density in the Active Region McMath 16288. D. PROJECTS UNDER DEVELOPMENT I. International Solar Polar Mission The ESA/NASA International Solar Polar Mission (ISPM) will be the first spacecraft to explore the heliosphere, within a few astronomical units from the sun, over the full range of heliographic latitudes. Its main objectives are to study the large-scale structure of the heliosphere, the solar wind, solar energetic particles and X-ray flares, galactic cosmic rays and inter-planetary dust as a function of heliolatitude (Wenzel, 1980). Since NASA decided to cancel its spacecraft, no solar imaging instrumentation will be carried on this mission. The launch of the ESA spacecraft is scheduled for May 1986 or earlier, if possible. The passages over the solar poles would occur in 1989-90. II. ESA-NASA Cooperation on Spacelab 1 Part of the payload for this flight (scheduled for mid-1983) is a package of solar irradiance measuring instruments consisting of - two absolute radiometers to measure the total irradiance, one built by the "Institut Royal Meteorologique de Belgique", Brussels and the Space Science Department of ESA, Noordwijk and the other by Jet Propulsion Laboratory, Pasadena, California. - a spectrometer that covers the range 170 - 3200 nm, built by Service d'Aeronomie du CNRS, Verrieres-Ie-Buisson; Institut d'Aeronomie, Brussels; Landessternwarte, Heidelberg and Hamburgersternwarte. To improve the accuracy of absolute values of the solar irradiance, the instrument performance will be determined before, during and after the flight. It is foreseen to refly the instrument package on future Spacelab missions, at intervals of about half to one year, to observe long term changes of the solar irradiance .

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III. Solar Optical Telescope (SOT) The next major solar physics space facility currently selected by NASA is the Solar Optical Telescope, a 1,25-meter diameter telescope for the optical and UV which will fly on the Shuttle starting in 1987, to perform high spatial resolution studies of the solar atmosphere and magnetic fields. SOT will have a resolution of better than 0,2 arc seconds. Two investigations have been selected: a) A combined Filtergraph Spectrograph which will include a tunable filtergraph-polarimeter for the visible and a visible and UV spectrograph; this will use large CCD arrays as detectors, and b) A visible and near UV photographic filtergraph which will have a somewhat larger field of view, extremely high resolution film, and short exposure times to try to test the ultimate performance of the SOT optics. IV. Soviet Solar Satellite The Institute for Cosmical Research in Moscow is preparing a three-axis stabilized spacecraft with solar instrumentation, to be launched in 1982 or 1983. Main instruments are solar high-resolution spectrometers, polarimeters and UV and X-ray imaging equipment. V. RASOLBA A balloon-borne telescope and spectrometer, with 30 cm aperture, prepared by Laboratoire de Physique Stellaire et Planetaire at Verrieres, France will operate between 2000 and 3000 A and is devoted to high-resolution spectroscopy of the photosphere, chromosphere and active regions. A CCD Ha camera will allow the choise of targets on the disc. The scientific objectives will concentrate on the heating mechanisms in the solar outer atmosphere. E. SOME PROJECTS UNDER CONSIDERATION I. DISCO DISCO is a proposal under consideration in the European Space Agency. It would be a 550 kg satellite orbiting the L1 Lagrangian point of the Sun-Earth system (0,01 AU from the Earth on the Earth-Sun line). It would be spin-stabilized with its spin-axis maintained in a sunward direction. Its primary scientific objectives may be described best by the "solar seismology". It would be the logical continuation of the early observations of solar oscillations from mountain altitudes (Clavery et al., 1979). Velocity oscillation observations with a precision of a few mm s-1 may be achieved from space measurements and would constrain the solar models to a better defined convection zone (Berthomieu et al., 1980). They would give access to the gravity modes which will probe the composition and rotation of the interior of the Sun from the upper layers down to the central core. DISCO will also refine the observation of changes of solar irradiance associated with solar activity observed by Willson (1981) on the Solar Maximum Mission, and the spectral observations of similar variations made by Frohlich (1980) from a balloon. The solar brightness oscillations observed by Deubner (1981) in reflected light by Uranus and Jupiter may be improved and the phase of the luminosity variations and velocity oscillations obtained. II. Grazing Incidence Solar Telescope (GRIST) GRIST would be a spacelab-borne telescope-spectrometer to be flown in conjunction with the second flight of SOT, and was the subject of an earlier study of ESA. It would operate between 7 nm and about 120 nm. Focal plane instruments are presently under study in various European institutes. The objectives of GRIST,

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its technological and scientific possibilities and constraints are described ~n a special issue of Space Science Reviews edited by Huber (1981). III. Solar Corona Explorer A proposal under consideration in NASA. The objectives are the continuous study of coronal structures and their developments, with a view to arrive at an understanding of their origin and evolution. References Acton, L.W. et al.: 1980, Solar Phys., 65, 39 Berthomieu, ~ooper, A.J., Gough, D.~, Osaki, Y., Provost, J. and Rocca, A.: 1980, in: Nonradial and Nonlinear Stellar Pulsation, H.A. Hill and W.A. Dziembowski, Eds., Springer-Verlag, Berlin Bohlin, J.D. et al.: 1980, Solar Phys., 65, 5 Bonnet, R.M.,~I.: 1980, Astrophys. J., 237, L 47 Bonnet, R.M.: ~ Space Sci. Rev., 29, 13-1Bonnet, R.M. et al.: 1982, Solar Phys~ 77. Claverie, A., Isaak, G.R., McLeod, C.P.,-Van der Raay, H.B. and Roca Cortes, T.: 1979, Nature, 282, p. 591 Deubner, F.L.: 1981~ature, 290, p. 682 Forrest, D.J. et al.: 1980, Solar Phys., 65,5 Frohlich, C.: 1980, Proceedings of the Workshop on Variations of the Solar Constant, G.S.F.C., Greenbelt, U.S.A., 5-7 November 1980 Grec, G., Fossat, E., Pomerantz, M.: 1980, Nature, 288, p. 541 Huber, M.C.: 1981, Space Sci. Rev., 29 -Huber, M.C. et al.: 1981, Appl.Opt, 20, 2139 Hudson, H.S.:-1981, High Energy Space-Research, vol. 1 (13) of Advances in Space Research Macqueen, R.M. et al.: 1980, Solar Phys., 65, 91 Orwig, L.E., et~ 1980, Solar Phys., 65, 25 Van Beek, H.F~ al.: 1980, Solar Phys., 65, 39 Wenzel, K.P.: 1980, Phil. Trans. R. Soc. Lond. A 297, p. 565 Willson, R.: 1981, in Physics of Solar Variations-l14th ESLAB Symposium), V. Domingo, Ed., Reidel Publ. Co. (Dordrecht), p. 217 Willson, R.: 1980, Solar Phys., 65, 109 Woodgate, B.E., et al.: 1980, Solar Phys. ~, 73

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6. Ga.'T_a-Ray Ast conony ~.t.. Peterson In the past feH yea,rs galLly,a-yay astronorr.y has rc,ade significant di scoveries , and has moved from an exploratory phase to a developing phase. Results from the High Energy Astronomical Observatories (HEAO-1 and HEAO-3), Cos-B, and balloons have shown that many galactic and extragalactic X-ray sources have time variable spectra extending into the feH MeV range. Variable annihilation radiation has been fOG-nd fro;']'; the galactic center, and Cos-B has resolved 'V 25 sources emitting in the> 30 MeV regime, as Hell as confirming a general emission in the galactic plane. The most remarkable progress has, hOHe'rer, occurred in the study of solar y-ray lines from the Solar Maximum Miss1,on (SMM) and of the ga."11'ls-ray burst phenomena. Observations of the latter were fron simple detectors placed on such spacecraft as the Vela series, Pioneer Venus Orbiter, Venera 11 and 12, ISEE-3, and Prognoz-7. Many of the recent results are summarized in the published Proceedings of a number of conferences devoted to the entire subject (Cowsik and Wills, Ed., 1980; H.S.W. Massey, et al. Eds. 1981), as Hell as those on specialized aspects (Hurley,Ed., 1981). In the folloHing, recent results are reviewed,based on technique and/or observation classifications. These include a) continuum emissions, ;;:, 20 keV which extend into the MeV range, b) gamma-ray line spectroscopy, including the sun, c) observations of the y-ray burst phenomena, and d) high-energy (2 30 MeV) astronomy. Finally, future plans and observational possibilities are indicated. A. CONTINUUM OBSERVATIONS (E ~ 20 keV) Although well over a thousand galactic and extragalactic sources have been discovered and studied from the HEAO-l and HEAO-2 (Einstein Observatory), most have soft spectra, KT ~ 3 keV, and therefore do not have fluxes extending beyond 'V 20 keV Sources of certain classes have "hard" spectra, characterized by a pOHer law d'! -y / 2 < . dE 'V E ph cm -sec-MeV, with 1 < Y 'V 3, and therefore may be dedectable In the 100 keV range or beyond. I.

Galactic Sources

X-ray pulsators in binary systems are believed to be accreting neutron stars wi th a remnant magnetic field Co 10 12 gauss. Gas flow from a main sequence companion star becomes ionized, is guided to the magnetic poles of the rotatin~ neutron star, Hhere it acquires energy on the order of 100 MeV/nucleon before being shocked into a high temperature plasma with T 'V 10 8 ~. A general property of these pulsators, whose periods range from 0.7 to > 100 sec., is a hard (y 'V 1) spectra below 30 keV, and a steepening of at least one index at higher ene~gies. Uineteen of these objects have been observed in the hard X-ray range and h'e=-_ter, 19(1). 'The most extensively studied member of this class is Her X-I. Trum~'er et aI. (1978) have observed a feature at 'V 45 keY, which may be due to cyclotron resonance transitions in the a 'V lOlLgauss field. Gruber et al. (1980) have confirmea these features and prQvided details on the variation or-pulse shape with rotation and orbital phase. Tuel1er et al. 1981 have measured these features with a high resolution Ge detector and these data have shown the feature is not a narrow emission or absorption line. Wheaton et al. (1979) have shown the transient X-ray pulsator 4UOl15+63 also has features likely due to cyclotron effects. The black hole candidate in a binary system, Cyg X-I, has a complex time variable spectra extending to over 200 keY (Nolan 1981a). The composite spectrum is thought to be due to soft X-rays originating in an accretion disc near the

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Schwarzchild radius, and Compton-scattering in an outer high temperature (T ~ 10 9 K) disc (Sunyaev & TrUmper, 1979). Nolan et al. (1981b) has also determined the average spectrum to ~ 2 MeV. Only minimal observations now exist on other X-ray black-hole candidates, GX339-04 and Cir X-I (Nolan, 1980; Samini et al., 1979, Sadeh et al., 1979); however they are known to have ~ 1 sec. variability at a few keV. The radio pulsars PSR 0531-22 (Crab) and PSR 0833-45 (Vela), having periods at ~ 33 and ~ 89 ms respectively, have been detected in ~ 50 MeV y-rays (Bennett, et al., 1977). Only upper limits exist for Vela pulsations < 10 MeV (Knight "et al.; 1980). Both pulsed and continuous emission from the Crab Nebula region have been extensively observed in the X-ray range since the beginning of X-ray astronomy. Recently the entire pulsed emission spectra has been characterized with a 3 component power law (Kundt and Krotscheck, 1980) and spectral variations with phase have been detected in both soft and hard X-rays (Pravdo & Serlemitsos, 1980; Knight, et al., 1980). II.

Extragalactic Sources

(E

The extragalactic sources thus far detected at the higher energies ~ 20 kev) are characterized by hard, non-thermal spectra, variability, and high luminosity, and are from galaxies with active nuclei. These include Seyfert's, Bl Lac objects, QSO's and certain radio galaxies. Some of these have been detected into the 100 keV range; in most cases the major luminosity is in hard X-rays. Dean and Ramsden (1981) have recently reviewed the data on extragalactic gamma-rays. The emission is often explained in term of direct radiation by Comptonization from an accretion disc surrounding a massive black-hole (l-1eszaros and Silk, 1977); or by synchrotron-self-Compton emission (SSC) from relativistic electrons, also produced by a massive black hole or other compact source (Jones, O'Dell and Stien, 1974; Mushotzky, 1977). The QSO 3C273 has been observed in 2-60 keV X-rays and at 13-120 keV (Primini et al., 1979) with HEAO-l and in high-energy y-rays (50-500 MeV), with Cos-B (Swanenberg et al., 1978). The total spectrum to 60 keV can be described by a power law spectral index y ~ - 1.6 and requires a steepening to connect with the Cos-B data. The variability observed in soft X-rays also energies. Although other QSO's have been observed at lower X-ray energies, none of these have yet been detected E ~ 20 keV. The Type 1 Seyfert galaxy, NGC 4151, has been most extensively studied, and fluxes have been reported to ~ 6 MeV, although these latter measurements are controversial (cf. Dean and Ramsden, 1981). Clearly, however, HEAO-l has detected 4151 to ~ 2 MeV (Baity et al., 1980) with evidence of ~ factor of two variability on a time scale of months (Meegan and Haymes, 1979). The spectra of other Seyferts have been determined and have a power law index typically -1.67 extending into the hard X-ray region (Mushotzky et al., 1980). In particular, MKN 509, (Dil et al., 1981), has been measured to have a hard X-ray spectrum to 73 keV and NGC 1275 in the Perseus cluster has been measured to over 200 keV, both with an index ~ -1.5 (Rothschild et al., 1981; Primini, et al., 1981). - The strong radio source Cen A has been extensively observed (Dean and Ramsden, 1981). Recent data over the 2 keV - 2.3 MeV range has shown the lower energy spectral index is ~ -1.65, breaking to ~ 2.0 at 140 keV. The source is also 50% variable over a 6 month period (Baity et al., 1981). Although only upper limits have been observed from Cen A in the 30-200 MeV range (Bignami, et al. 1979) a possible detection has been reported at E > 300 MeV (Grindley, et al. 1975).

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Although the principal X-ray emission from cluster sources such as Virgo (Lea et al., 1981) and Perseus (Primini, et al., 1981) is soft (KT ~ 6 keV), these sources also have a hard component which has been determined to ~ 200 keV. This emission may be from either compact active galaxies in the cluster, or from Compton scattering by relativistic electrons on photons in the intercluster medium. B.

NUCLEAR GAMMA-RAY SPECTROSCOPY

Mono-energetic y-ray lines have long been predicted to originate from solar flares and from cosmic sources due to such processes as radioactivity in supernovae remnants, novae, or the interstellar medium; capture and inelastic scattering of energetic protons and neutrons; and position-electron annihilation phenomena (Ramaty & Lingenfelter, 1979). Many of these phenomena have now been measured in certain source locations, and significant upper limits to other predicted processes are available. Cyclotron line emission, which is a phenomena of electromagnetic rather than nuclear origin has been discovered in the binary X-ray systems Her X-l and 4UOl15+63, as discussed here previously. This feature also has apparently been observed in y-ray bursts. 1.

Solar Flares

The initial observation of extra-terrestial y-ray lines was in the great solar flare of 4 Aug. 1972. Features were seen at 0.51 MeV due to positron annihilation; 2.2 MeV due to neutron capture on hydrogen forming deuterium; and at 4.4 and 6.13 MeV due to de-excitation of *C 12 and *0 16 , respectively (Chupp et al., 1973). Since then the 2.2 and 4.4 MeV lines were observed by HEAO-l in the white light flare of 11 July 1978 (Hudson et al., 1980) and in a number of flares by SMM (Chupp et al., 1981;· Ryan et a~ 1981). All these are accompanied by a strong X- and y-ray continuum extending to ~ 7 MeV. The width of the 2.2 MeV line has been determined to be less than ~ 3 keV in the flare of 9 Nov. 1979 from the Ge spectrometer on HEAO-3 (Prince et al., 1982). The narrow width of this line, and its delay of 1-2 min. from the prompt 4.4 and 6.13 MeV lines, are consistent with neutron production in the lower chromospheric region of the flare and therma1ization followed by capture in the photosphere. The NaI spectrometer on the SMM has, in addition to the 7 June 1980 event, observed several more flares producing y-ray lines. Analysis (Ramaty and Lingenfelter, 1981) shows that the nuclei must be accelerated near the flash phase of the flare, that the y-rays are produced by accelerated particles trapped at the Sun, and that the total nucleonic energy deposited in the photosphere is only a small fraction of the total flare energy. 2.

Galactic Center Region

Gamma-ray emission near 0.511 MeV, positively detected in a balloon observation oy Leventhal et al. (1978) has been confirmed and studied further using the Ge spectrometer ~ HEAO-3 (Riegler, et al., 1981). The emission is confined to a region small compared to the 30 0 FWHM of the detector, has a line-width less than 3 keV at 0.511 MeV and had a strength of ~ 1.8 x·lO- 3 ph/cm 2 -sec in Sept. 1979, consistant with that of Leventhal. Most remarkable, however, was the decrease in intensity to 0.65 x· ·10- 3 six months later. This observation requires that the annihilation source be a discrete ob.iect near the galactic center, less than 1 light year across, and that the region be a relativelY high density, partially ionized gas of T < 10 5 K (Ramaty and Lingenfelter, 1981). Because of the large number of hard X-ray sources within a few degrees of the galactic center (Levine et al., 1980) the relation of these sources with the 0.511 emission region: if any, is unclear, as is the association with other structures near the galactic center (Ramaty and Lingenfelter, 1981). OJ

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Other possible y-ray line emissions in the galactic plane due to the integrated effects of supernovae production (nucleosynthesis) and cosmic-rays interacting in the interstellar medium (Ramaty and Lingenfelter 1979) have not been observed. Significant upper limits on such lines as Al i6 (1.809 MeV),Co 60 (0.847, 1.238 MeV), Ti44 (.068, .078, 1.156 MeV) are forthcoming from HEAO-3. Earlier reported fluxes at 4.4 MeV from the galactic plane (Haymes. et al. 1975) seem not to have been confirmed (Mat~eson et al., 1980). 3.

Extragalactic Sources

Only upper limits on y-ray lines are available at the "v 10- 3 ph/_cr:-. 2 -sec flux level for a few sources, notably active galactic nuc'-ei. FDr exa:c.:;le the 3iJlimit on 0.511 emission from Cen A is 1.2 X 10- 3 ph/cm 2 -sec. ::i:all e~ al., ':'9 5;. Gamma-ray lines at ~ 1.6 and at ~ 4.4 MeV has also been reported by Ha':'':', et a':'., (1975) for this source; however, these results are unconfirmed. 7

C.

GAMMA-RAY BURSTS

Since the discovery in 1969 of short (~ 1-10 sec.), intense (> 10- 5 ergs/ cm 2 sec) bursts of cosmic origin in the 50 keV ~ E ~ 1 MeV range, over 100 of these events have been observed, some with intensities as weak as 3 x 10- 6 ergs/sec. By the end of 1978 a series of interplanetary spacecraft including the Pioneer Venus Orbiter, Venera 11 and 12, ISEE-3, and HELIOS-2 were launched and formed, together with near-earth spacecraft, an interplanetary triangulation timing network. The specialized instruments permitted the location of some bursts on the celestial sphere to arc-minute accuracy. Hurley (1980) has reviewed the observational situation and provided a catalog of the 62 confirmed events detected through mid 1978. Through 1980 about 40 confirmed additional events have been discovered (Vedrenne, 1981) by the interplanetary network, and even more from the Venera 11 and 12 (Mazets, et aI., 1979a; 19tH). 1.

Ln N - Ln S

The interpretation of the Ln N-Ln S curve for burst distribution has proven difficult (Vedrenne 1981). Observational data sets by different instruments fail to agree either in shape or the normalization of the event sets. For example, the most complete set of qata (Mazets et al., 1980; 1981), seems fully a factor 2 of three above the Vela and Imp-7 results in the range 2 x 10- 5 < S< 2 x 10- ergs/cm . Furthermore, the shape of this curve is dependent on assumptions regarding the astrophysical model selected (Jennings and White, 1980). At present, comparison of observed and predicted distributions seems to favor a galactic origin for most of the bursts. 2.

Spectra and Time Variations

The rather more sophisticated instruments on the spacecraft of the interplanetary network have allowed the detailed study of the time structure of many bursts and permitted attempts at classification (Barat et aI., 1981; Mazets et al., 1981). Bursts are now observed with durations from ~ 0.1-100 sec.; many events have numerous peaks; some of these are highly structured with individual pulses as short as 2 ms. Apparently a two-peaked recurrent structure with individual peaks spaced 2-3 sec. is common. Only one burst, the uni~ue 5 March 1979 (Mazets, et al. , 1979b) event shows a distinct periodicity of 8.0 ± .02 sec. form

Although the time-averaged spectra are generally consistent with the exponential

~~ ~ e-E/Eo (Eo ~ 150 keV), considerable spectral variations and structure have now been observed (Vedrenne, 1981; Barat, et a1. 1981; Mazets et al., 1981).

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Knight et al. (1980) have noted spectral evolution and detected fluxes to over 2 MeV in the events of 20 Oct. 1977, and 10 Nov. 1977. Gamma-ray emission and absorption features have now been reported from many bursts, mostly by Mazets and co-workers (Mazets & Golenentski, 1981; Mazets et al., 1981). The principal emission lines are in the 400-460 keY range, while the absorption features--lie in the 30-60 keY range. The emission lines are interpreted as red shifted (Z ~ .2) positron annihilation and the absorption features are thought to be cyclotron absorption in strong (~1012G.) magnetic field. Both of these results strongly suggest a magnetized neutron star as the burst source. The event of 'i9 Nov. 1978 was also observed by the Ge detector on ISEE-3 (Teegarden & Cline, 1980) to have features not only at 400 keY, but also at740 keY. The latter may be interpreted as red-shifted (Z ~ 0.25) 847 keY emission from the first excited state of Fe - 56. 3.

Locations

About 6 events have now been located with enough preclslon (~ 1') for deep optical searches; perhaps another 6 are localized to within ~ 0.5 0 (Vedrenne, 1981). The unique 5 Mar. 1979 event, which was characterized by a very fastrising, intense (~ 2 x 10- 3 ergs/cm 2-sec), main burst with a 420 keY line feature, followed by an ~ 8 sec. periodicity, has been localized to a 6" x 30" error box (Evans et al., 1980; Vedrenne et al., 1980). This lies within the supernova remnant N49 in the LMC, which at a distance of 55 kpc, requires a luminosity of 3 x 10""ergs/sec., about 10 5 -10': more than that of a typical galactic source. Searches at other locations are beginning to reveal interesting optical and X-ray counterparts. The error box for the event of 19 Nov. 1978 (Cline et al., 1981) may-contain weak X-ray emission detected by Einstein as well as a-weak radio source (Vedrenne, 1981) and it appears to be the site of an optical burst in 1928 (Schaefer 1981). J. HIGH ENERGY (> 30 MeV) ASTRONOMY Cos-B Catalogue

. t ~he Cos-B satellite, constructed and operated by the Caravane collaboratlon , was launched in Aug. 1975 and has continued to operate successfully. The spark chamber operates between ~ 30-500 MeV, and has an area of ~ 600 cm 2 • Since the publication of the first catalog of y-ray sources (Hermsen et al., 1977), a Eore systematic survey has been completed, and a new 2nd catalog issued (Hermsen 1980; Swanenberg et al., 1981). This catalog contains 25 detected sources, ~ostly clustered in the galactic plane, having intensities> 100 MeV typically of > :0- 6 ph/cm 2 -sec, and positional error circles ~ 1 0 radius. ~t present, only 4 of these sources are identified with known radio, optical, or X-ray sources. The identification with radio pulsar PSR 0531 + 21 (Crab) and PSR 0833-45 (Vela) is through their timing signatures. Positional coincidence associates 2CG289+64 .rith 3C273, and 2CG353+16, with the p-Oph cloud cor::plex. Most Cos-B error circles fail to associate with known galactic objects such as strong X-ray sources, radio pulsars, galactic structures, etc. More detailed and systematic searches on a few sources have turned up only suggested candidates (Caraveo, 1981).

tCosmic Ray Working Group, Huygens Laboratium, Leiden, The Netherlands. Istituto di Fisica Cosmica del C.N.R., Milan, Italy. Istituto di Fisica Universita di Palermo, Italy. Max-Planck Institut fur Estraterrestrische Physik, Garching bei Munchen, F.R.G. Service d'ElectroniquePhyslque, Centre d'Etudes Nucleaires de Saclay, France. Space Science Department of E.S.A., ESTEC, Noordwijk, The Netherlands.

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Diffuse Galactic Emission

As initially discovered by OSO-3, and studied in detail by SAS-2 (Fichtel et al. 1978), a y-ray map of the galaxy, after correcting for known point sources, reveals diffuse em~ssion in a '.'ridge" ~long the gala:,tic plane bMayer-Hasselwander ~t al. , 1980). Thls has a tYPlcal latltude scale helght of '" 3 , with structure in longitude associated with spiral arms and perhaps with more local phenomena, such as HI distributions, clouds, etc. Bignami (1981) has reviewed the interpretations of this emission in terms of a true diffuse component, due to a cosmic-ray dj.stribution interacting in the interstellar medium, or a cOllection of sources un",esolved by the Cos-B point-spread angular response function. The matter is fit p",esent not solved. The total emission of the galaxy is > 2 X 10 38 ergs/sec in ' 100 MeV photons; only abo'Jt 5% of this is in the ~ow-latitude sources of the 2nj Cos-2 catalog.

3.

Identified Sources

The Crab and Vela radio pulsar have been observed by Cos-B (Bennett et al., 1977) at their periods of 33 and 89 ms, respectively. There are many interesting comparisons and contrasts between these objects, the only radio pulsar s yet detected in y-rays, despite intensive searches. Both have a nearly similar double-pulse structure in y-rays. The Crab shows a similar double pulse structure at all observed wavelengths; radio, optical and X-ray, while Vela has only a single radio pulse, a very weak (relative to the Crab) optical double-pulse, and no confirmed X-ray pulse. The QSO 3C273 is the only detected extragalactic source at E > 30 MeV (Swanenberg, 1978). As discussed earlier, the spectrum must exhibit a steepening or break in a power-law form between'" 30 keV and 30 MeV. The other source is tentatively associated with the dark molecuJar cloud near p-Ophiuchus (Wills et al., 1980; Bignami and Morfill, 1980). This source may be due to enhanced y-ray production by a uniform (throughout the galaxy) cosmic-ray flux interacting in the locally increased density region (Issa and 'ri-pei, 1981); a contrary view (Morfill et al., 1980) is that an enhanced cosmicray density trapped in the cloud is required.

E.

FUTURE PROSPECTS

The future of y-ray astronomy depends largely on dedicated observatory class space missions significant instruments on other missions, or on improved capability for specific balloon measurements (Fichtel, 1981). The Gamma-Ray Observatory, to be launched by NASA in 1988, contains a set of complementary instruments extending from'" 50 keV to over 10 GeV. The FrancoSoviet spark chamber Gamma-I is expected to be launched in 1988. The Vela spacec",aft, Pioneer Venus Orbiter, Venera 11 and 12 and Helios-2 will continue as an interplanetary burst network for some time. To that will be added additional instrurr"ents on future Venera missions, and on the single remaining spacecraft of the International Solar Polar Mission (ISPM). NASA's X-ray Timing Explorer (XTE) may contain an instrument provi ding coverage of the extended X-ray spectnun to '" 250 keV.

4

Finally, limited observations at high resolution for cosmic y-ray line spectroscopy will be obtained using cooled Ge counters of large area on enhanced balloon programs being planned both in the U.S., and in Europe.

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References Cowsik, R. & Wills, R.D., eds.: 1980, Pergamon Press, 276 pgs. Massey, M.S.W., Wills, R.D. & Wolfendale, A.W., eds.: 1981, Phil. Trans. R. Soc. London. A-301, p. 495-703. Hurley, K.: 1981, Astro. and Sp. Sci. 75, p. 3-224. Wang, Y.-M. & Welter, G.L.: 1981, Astron. Astrophys. 102, p. 97. TrUmper, J., Pietsch, W., Reppin, C., Voges, W., Staubert, R., & Kendziorra, E.: 1978, Astrophys. J. Lett. 219, LI05. Gruber, D.E., Matteson, J.L., Nolan, P.I,., Knight, F.K., Baity, W.A., Rothschild, R.E., Peterson, L.E., Hoffman, J.A., Scheepmaker, A., Wheaton, W.A., Primini, F.A., Levine, A.M., & Lewin, W.H.G.: 1980, Astrophys. J. Lett. 240, L127. Tueller, J., Cline, T., Paciesas, W., Teegarden, B., Boclet, D., Dorouchoux, P., Hamenry, J., and Haymes, R.: 1981, Goddard Space Flight Center preprint, XG 3-1wneaton, W.A., Doty, J.P., Primini, F.A., Co'oke, B.A., Dobson, C.A., Goldman, A., Hecht, M., Hoffman, J.A., Howe, S.K., Scheepmaker, A., Tsiang, E.Y., Lewin, W.H,G., Matteson, J.L., Gruber, D.E., Baity, W.A., Rothschild, R.E., Knight, F.K., Nolan, P., & Peterson, L.E .. : 1979, Nature, 282, 240. Nolan, P.L., Gruber, D.E., Knight, F.K., Matteson, J.L., Rothschild, R.E., Marshall, F.E., Levine, A.M., & Primini, F.A.: 1981b, Nature, 293, 275. Sunyaev, R.A., & TrUmper, J.: 1979, Nature, 279, 506. --Nolan, P.L., Gruber, D.E., Matteson, J.L., Peterson, L.E., Rothschild, R.E., Doty, J.P., Levine, A.M., Lewin, W.H.G., & 'Primini, F.A., 1981a, Astrophys. J., 246, 494. Nolan, P.~980, B.A.A.S. 12, 857. Samimi, J., Share, G.H., Wood, K., Yentis, D., Meekins, J., Evans, W.D., Shulman, S., Byram, E.T., Chubb, T.A., & Friedman, H.: 1979, Nature, 278, 434. Sadeh, D., Meridav, M., Wood, K., Yentis, D., Smothers, H., Meckins, J., Evans, W., Byram, E.T., Chubb, T.A., & Friedman, H.: 1979, Nature, 278, 436. Bennett, K., Bignami, G.F., Boella, G., Buccheri, R., Hermsen, W., Kanbach, G., Lichti, G.G., Masnou, J.L., Mayer-Hasselwander, H.A., Paul, J.A., Scarsi, L., Swanenburg, B.N., Taylor, B.G., & Wills, R.D.: 1977, Astron. Astrophys., 61,279. Kundt, W., and Krotscheck, E.: 1980, Astron. Astrophys. 83,1. -Pravdo, S.H., & Serlemitsos, P.J.: 1980, B.A.A.S. 11, 70~ Knight, F.K., Baity, W.A., Gruber, D.E., Peterson, L.E., Bautz, M., Lang, F., & Lewin, W.H.G.: 1980, B.A.A.S. 12,541. Meszaros, P. & Silk, J.: 1977, Astron~Astrophys., 55,289. Jones, T.I-i., O'Dell, S.L., & Stein, W.: 1974, Astrophys. J., 192, 261Mushotzky, R.F.: 1977, Nature, 265, 225. \vorrall, D.M., Mushotzky, R.F., Boldt, E.A., Holt, S.S. & Serlemitsos, P.J.: 1979, Astrophys. J., 232, 683. Primini, F.A., Cooke, B.A., Dobson, C.A., Howe, S.K., Scheepmaker, A., Wheaton, ~·l.A., Lewin, W.H.G., BAity, W.A., Gruber, D.E., Matteson, J .L. & Peterson, L.E.: 1979, Nature, 278, 234. Swanenberg, B. N., Bennett, K., Bignami, G.F., Caravco, P., Hermsen, H., Kanbach, G., Masnou, J.L., Mayer-Hasselwander, H.A., Paul, J.A., Sacco, B., Scarsi, L. & Wills, R.D.: 1978, Nature, Lond. 275, 298. Dean, A.J. & Ramsden, D.: 1981, Phil. Trans. R. Soc. Lond. A301, S77. Baity, W.A., Rothschild, R.E., Worrall, D.M., Peterson, L.E., Primini, F.A., Levine, A.M. & Lewin, W.H.G.: 1980, B.A.A.S., 12, 802. Meegan, C.A. & Haymes, R.C.: 1979, Astrophys. J., 233, 510. Mushotzky, R.F., Marshall, F.E., Boldt, E.A., Holt~.S. & Serlemitsos, P.J.: 1980, Astrophys. J., 235, 377. Dil, S., Primini, F.A., Basinska, E., BAutz, M., Howe, S.K., Lang, F., Levine, A.M., Lewin, W.H.G., Worrall, D.M., Nolan, P.L. & Matteson, J.L.: 1981, Astrophys. J. accepted for publication. Rothschild, R.E., Baity, W.A., Marscher, A.P. & Wheaton, W.A.: 1981, Astrophys. J. Lett. 243, L9.

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Baity, W.A., Rothschild, R.E., Lingenfelter, R.E., Stein, W.A., Nolan, P.L., Gruber, D.E., Knight, F.K., Matteson, J.L., Peterson, L.E., Primini, F.A., Levine, A.M., Lewin, W.H.G., Mushotzky, R.F. & Tennard, A.F.: 1981, Astrophys. J., 2h4, 429. Bignami, G.F., Fichte~ C.E., Hartman, R.C. & Thompson, D.J.: 1979, Astrophys. J., 232, 649. Grindlay, J.E., Helmken, H.K., Hanbury Brown, R., Davis, J., & Allen, L.R.: 1975, Astrophys. J., l~ L9. Lea, S.M., Reichert, G., Mushotzky, R., Baity, W.A., Gruber, D.E., Rothschild, R.E. & Primini, F.A.: 1981, Astrophys. J., 246, 369. Primini, F.A., Basinska, E., Howe, S.K., Lang, F., Levine, A.N., Lewin, W.H.G., Rothschild, R.E., Baity, W.A., Gruber, D.E., Matteson, J.L., Peterson, L.E., Lea, S.M., & Reichert, G.A.: 1981, Astrophys. J. Lett. 243, L13. Ramaty, R. & Lingenfelter, R.E.: 1979, Nature, 278, 127. Chupp, et al.: 1973, Nature, 241, 333. -Hudson, H.S., Bai, T., Gruber, D.E., Matteson, J.L., Nolan, P.L. & Peterson, L.E.: 1980, Astrophys. J., 236, L91. Chupp, E.L., Forrest, D.J.~yan, J.M., Cherry, M.L., Reppin, C., Kanbach, G., Rieger, E., Pinkau, K., Share, G.H., Kinzer, R.L., Strickman, M.S., Johnson, W.N. & Kurfess, J.D.: 1981, Astrophys. J., 244, L171. Prince, T.A., Ling, J.C., Mahoney, W.A., Riegler~.R., Jacobson, A.S.: 1982, Astrophys. J. Lett., in press. Ramaty, R. & Lingenfelter, R.E.: 1981, Phil. Trans. R. Soc. London, A301, 671. Leventhal, M., MacCallum, C.J. & Stang, P.D.: 1978, Astrophys. J., 223, Lll. Riegler, G.R., Ling, J.C., Mahoney, W.A., Wheaton, W.A., Willett, J.B., Jacobson, A.S., & Prince, T.A., 1981, Astrophys. J. Lett., 248, L13. Levine, A., Bfutz, M., Howe, S., Lang, F., Primini, F., Lewin, W.H.G., Baity, W., Gruber, D., Knight, F., Peterson, L., Rothschild, R., Matteson, J. & Nolan, P.: 1980, B.A.A.S., 12, 463. Haymes, R.C., Walraven, G.D., Meegan, C.A., Hall, R.D., Djuth, F.T. & Shelton, D.H.: 1975, Astrophys. J., 201, 593. Hall, R.D., Meegan, C.A., Walraven, G.D., Djuth, F.T. & Haymes, R.C.: 1976, Astrophys. J., 210, 631. Hurley, K.: 1980, Non-Solar Gamma-Rays Adv. Space Exploration 7,123 (Ed. R. Cowsik and R.D. Wills) Oxford: Pergamon Press. Vedrenne, G.: 1981, Phil. Trans. R. Soc. Lond., A301, 645. Mazets, E.P., Golenetskii, S.V. & Gur'yan, Yu.A.: 1979a Pis'illa Astron. Zh. 2,641. Mazets, E.P., Golenetskii, S.V., Il'Inskii, V.N., Panov, V.N., Aptekar, R.L., Gur'Yan, Yu.A., Proskura, M.P., Sokolov, I.A., Sokolova, Z. Ya., & Kharitonova, T.V.: 1981, Astrophys. & Space Sci., 8o, 3. Jennings, M.C. & White, R.S.: 1980, Astrophys. J., 238, 110. Barat, C., Chambon, G., Hurley, K., Niel, M., Vedre;:;;:;:e, G., Estulin, I.V., Kuznetsov, A.V. & Zenchenko, V.M.: 1981, Astrophys. Space Sci. 75,83. Terrel, J., Evans, H.D., Klebesadel, R.W. & Laros, J.G.: 198o, Nature, Lond. 285,383. Mazets, E.P. et al.: 1979b Nature, 282, 587. Knight, F.K.,lMatteson, J.L. & Peterson, L.E.: 1981, Astrophys. Space Sci. ]2,21. Mazets, E.P. & Golenetskii, S.V.: 1981, Astrophys. Space Sci., ]2,47. Teegarden, B.J. & Cline, T.L.: 1980, Astrophys. J. Lett, 236, L67. Cline, T.L., Desai, U.D., Pizzichini, G., Teegarden, B.J., Evans, W.D., Klebesadel, R.W., Laros, J.G., Barat, C., Hurley, K., Niel, M., Vedrenne, F., Estulin, I.V., Mersov, G.A., Zenchenko, V.M. & Kurt, V.G.: 1981, Astrophys. J. Lett., 248, L133. Vedrenne, G., Zenchenko, V.M., Kurt, V.G., Niel, M., Hurley, K. & Estullin, I.V.: 1980, Soviet Astr. Lett. 2, 314. Evans, W.D., Klebesadel, R.W., Laros, J.G., Cline, T.L., Desai, U.D., Hurley, K., Niel, M., Vedrenne, G., Estu1in, I.V., Kuznetsov, A.V. & Zenchenko, V.M.: 1980, Astrophys. J. Lett., 237, L7. Schaefer, B.E.: 1981, Nature, in press.

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H., Swanenburg, B.N., Bignami, G.F., Boella, G., Buccheri, R., Scarsi, Kanbach, G., J.layer-Hasselwander, H.A., Masnou, J.L., Paul, J.A., 3ennett, K., Higdon, J.L., Lichti, G.G., Taylor, B.G. & Wills, R.D.: 1977, Nat~re Land., 269, 494. Hermson, W.: 1981, Phil. Trans. R. Soc. London, A301, 519. Caraveo, P.: 1981, Phil. Trans. R. Soc. London, A301, 523. Mayer-Hasse1wander, H. A., Bennett, K., Bignami, G. F., B'~ccheri, R., d' Amico, N., Hermsen, 1,1., Kanbach, G., Lebrun, P., Lichti, G.G., Masnou, J.L., Paul, J.A., Pinkau, K., Scarsi, L., Swanenburg, B.N. & Wills, R.D.: 1980, Ninth Texas Symposium on Relativistic Astrophysics, Ann. N.Y. Acad. Sci., 336, 211. Swanenberg, B. N. et a].: 1981, Astrophys. J. 243, L69. -Bignami, G.P.: 1981, Phil. Trans. R. Soc. London, A301, 555. Bennett, K., Bignami, G.F., Boel1a, G., Buccheri, R., Hermsen, W., Kanbach, G., Lichti, G.G., Masnou, J.L., Mayer-Hasse1wander, H.A., Paul, J.A., Scarsi, L., Swanenburg, B.N., Taylor, B.G. & ~lills, R.D.: 1977, Astron. Astrophys., 61, 279. Wills, R.D., Bennett, K., Bignami, G.P., Buccheri, R., Caraveo, P., d'Amico, N., Hermsen, W., Kanbach, G., Lichti, G.G., Masnou, J.L., Mayer-Hasselwander, H.A., Paul, J.A., Sacco, B. & Swanenburg, B.N.: 1980, COSPAR Symposium on Non-Solar Gamma-Rays, In Adv. in Space Explor. (ed. R. Cowsik & R.D. Wills), vol. 7, p. 43. Oxford: Pergamon Press. Issa, M.R. & Ti-pei, L.: 1981, Phil. Trans. R. Soc. London, A301, 533. Bignami, G.F. & Morfill, G.E.: 1980, Astron. Astrophys. 87, ~errnsen, ~.,

as:-

Morfill, G.E., Volk, H.J., Forman,--M., Bignami, G.F., Caraveo, P.A. & Drury, L.:

1980, Astrophys. J., 246, 810. Pichte1, C.E.: 1981, Phil. Trans. R. Soc. London, A301, 693. Ryan, J.M., Forrest, D.J., Chupp, E.L., Cherry, M.L., Reppin, C., Rieger, E., Pinkau, K., Kanbach, G., Share, G.H., Kinser, R.L., Strickman, M.S., Johnson, W.N. & Kurfess, J.D.: 1981, Astrophys. J. Lett., 244, L175.

45. STELLAR CLASSIFICATION (CLASSIFICATION STELLAIRE) PRESIDENT: A. Slettebak VICE-PRESIDENT: V. L. Straizys ORGANIZING COMMITTEE: A. L. Ardeberg, R. A. Bartaya, R. A. Bell, R. F. Garrison, B. Hauck, M. Jaschek, A. G. D. Philip I.

INTRODUCTION

The years covered in this report (1979-81) have been active ones in the field of stellar classification, as is made obvious in the following sections. In addition to the individual references listed there, a number of symposia, colloquia, and workshops were held during the report period which included papers relevant to stellar classification. These include IAU Symposia 85 (Starclusters), 98 (Be stars), and 99 (Wolf-Rayet stars); IAU Colloquia 64 (Automated Data Retrieval in Astronomy) and 68 (Astrophysical Parameters for Globular Clusters); and the Dudley Observatory Workshop on Problems of Calibration of Multicolor Photometric·Systems (1979). II. (a)

CLASSIFICATION USING SLIT SPECTROSCOPY (R. F. Garrison)

0- and B-type Stars.

Identifications and classifications of X-ray and extreme UV stars have been made by several groups including Cowley, Crampton and Hutchings (21.114.566, 22.142.052, 22.142.047, 25.142.048, 26.116.008), Giangrande et al. (27.114.126), Walborn and Panek (PASP 92, 803, 1980), and Hammerschlag-Hensberge et al. (25.114.150) . Lundstr8m and Stenholm have classified 19 faint WR stars (25.113.013). Turner, Lyons and Bolton (22.114.501) have found a new Be star and Jaschek et al. have classified 5000 spectra of 140 Be stars taken over 20 years (28.114.050). Slettebak recently completed classification of all Be stars brighter than 6.0. Swings (A&A 98, 112, 1981) has classified CPD-52° 9243, an IR excess star with P-Cygni lines. Hirata (22.123.035) has noted that 88 Her is a shell star of Pleione type. Hydrogen deficient subdwarfs have been studied by Hunger and Kudritzki (28.126.003) and Drilling (21.114.563, 28.114.135) while Kaufmann and Theil have provided an atlas (27.114.190). Bisiacchi et al. have suggested that HD 93521 is a population II supergiant (22.114.574) and Walborn (ApJ 243, L37, 1981) has noted variations in the spectrum of the well-known star 6 1 Orionis C. Forte and Orsatti (AstrJ 86, 209, 1981) have classified OB stars in the field of the Carina Nebula. Muzzio and Levato have classified a distant supergiant in Norma (27.114.143) and Chromey has classified some faint stars in the anti-center direction (25.114.068, 28.114.027). Morgan has given revised distances for OB stars in the north galactic pole region. (b)

A- and F-Type Stars.

Morgan et al. have studied the Hertzsprung gap supergiants (ApJ 243, 894, 1981). Classifications have been carried out by A. Cowley and Bidelman of 310 bright FO-G5 stars north of _25 0 (25.114.127). Garrison has classified HD 219150 (28.113.002) . Drilling has illustrated two hydrogen deficient A stars (25.114.057) • Some high-latitude blue variables have been classified by Bond (22.122.209). "Numerical taxonomy" of Ap and Am stars has been carried out by C. Cowley and Henry (26.114.046) and 0 Scuti stars have been classified by Pena et al. (PASP 93,234,1981) and by Burke and Mayor (A&A 97,4,1981). Bp and Ap stars have been classified by Glagolevsky and Kopylov et al. (Sov. Astron. Letters 621

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7, 366; Corom. Special Ap. Obs. No. 30, 32; and Izvest. Special Ap. Obs. 13, 3). (c)

Late-type Stars.

This was a rich period for studies of late-type stars. Keenan and Pitts have given revised types for 552 stars (27.114.188). Strobel has given quantitative 3-dimensional classifications of FGK stars (26.114.131). A revised system in the red for S stars has been presented by Ake (26.114.089) while Keenan and Boeshaar have classified 101 Sand SC stars on the revised MK system (27.114.075). A more accurate HR diagram for the cooler stars has been given by Keenan (22.114.012), M stars have been classified in the near infrared by Solf (22.114.055) and Bidelman has classified stars of the Cal Tech two-micron survey (27.114.180). Metal weak stars have been studied by Bessell (21.114.546), Bessel and Ianna (21.126.034) and Foy (26.114.042). VV Cephei systems have been studied by Forte and Orsatti (27.119.042) and by Drilling (25.119.003). Fernie and Garrison (PASP 93, 330, 1981) have reclassified HD 179315 as a Cepheid of early type and Bouw has devised a system of classification for middle-type supergiants in the photographic IR (PASP 93, 45, 1981). (d)

Binaries.

Corbally and Garrison carried out classifications for 30 close visual double stars (28.118.023) and Corbally is extending the study. New types for spectroscopic binaries have been given by Hendry (21.119.013, 21.119.017), Keenan (28.114.149), Conti et a1. (27.120.030), Hutchings et a1. (22.142.047), and Bopp et a1. (26.120.015). Hot companions for supergiants have been classified by Parsons (ApJ 245, 201, 1981). (e)

Variable Stars.

Gauthier and Crowe, working with Garrison, are studying the spectra of Cepheids and Miras (respectively) around their cycles. Romanov et al. have studied RR Lyrae (28.122.096). (f)

Clusters and Associations.

Considerable work has been published during this period, especially by Abt and Levato who are continuing their important series of studies (27.153.054, 27.153.052, 26.153.030, 25.114.020, 25.153.048, 21.114.062, 22.114.011, and 28.153.002). Abt has also classified 865 components of visual multiple stars (ApJ Suppl 45, 437, 1981). Garrison and Schild classified stars in NGC 6231 down to AO on the main sequence (26.153.003). Van Rensbergen et al. search 5 clusters for Ap stars (21.153.012). FitzGerald et al. have studied many southern clusters using image tube spectra (26.114.024, 26.153.002). Pilachowski and Bonsack have studied yellow giants in open clusters (22.114.034). Individual clusters have been studied by Rydgren (27.152.004), I1arraco and Rydgren (AstrJ 86, 62), Claria and Rosenzweig (21.153.023), Perry et a1. (21.153.025), Harris and Harris (22.153.036), Turner et al. (22.153.026, 25.153.083, 27.152.001, 28.152.003, 28.153.008, PASP 92,840, 1981), Feinstein et a1. (27.153.066), and Barry et a1. (26.153.011) • Individual stars in globular clusters have been classified by Canizares et al. (21.154.017), West and Bartaya (26.154.009), and Remillard et al. (25.126.031) . Barry (25.120.020) has found a possible RS CVn star in the coma cluster and has studied differences between solar type stars and the Sun (21.114.004). Herbst et al. have classified newly formed stars in Canis Major RI (21.152.005) •

STELLAR CLASSIFICA TION

(g)

623

Stars in Galaxies.

With new detectors, individual stars in nearby galaxies are being observed in greater numbers. Crampton (25.159.017) has classified 25 OB stars in the LMC and Walborn (22.132.009) has found an 04 star in the SMC. WR stars have been classified by Melnick (22.114.549), Azzopardi and Breysacher (25.159.016), and Breysacher and Westerlund (21.114.570). Late type stars in the clouds have been classified by Humphreys (25.159.008,25.159.022), Feast (25.114.027), and Elias et al. (28.114.134). Carbon stars have been classified by Richer (ApJ 243, 744, 1981), Richer and Frogel (28.114.133), and Lloyd-Evans (28.114.047). Cowley et al. (21.114.010) have classified giant stars in distant satellites of the Galaxy, while Humphreys (27.158.238) and van den Bergh and Humphreys (25.158.149) have studied the most luminous stars in NGC 6822 and IC 1613. Humphreys has also classified stars in M 31 (26.158.196) and in M 33 (28.158.168) as well as M 101 and NGC 2403 (28.158.196). (h)

General.

Morgan et al. have made some important philosophical comments in their paper on the Hertzsprung gap supergiants (ApJ 243, 894, 1981). Morgan has also published remarks in the HR diagram symposiu,m (22.115 .U10) and in the Vatican Colloquium (25.114.090). Slettebak et al. have considered the effects of rotation on classification (28.114.131). Abt et al. have classified stars with unusual photometric indices (25.113.050) and the Jascheks have classified stars with satellite UV spectral peculiarities (28.114.051). Allen has classified Stephenson-Sanduleak emission-line stars (22.114.021) and Bychkov et al. (21.119.009) have studied classification in the IR. Komarov and Tsymbal have studied classification criteria theoretically (28.064.044). III.

OBJECTIVE-PRISM SPECTRAL CLASSIFICATION AND CLASSIFICATION INVOLVING AUTOMATIC METHODS (D. J. MacConnell)

N. Houk continues her important work of classifying the southern HD stars on plates taken with the Curtis Schmidt telescope (l08 R/mm at Hy). Volume 3 (Dec. _40 0 to _26 0 ) will be in press by early 1982 and may be accompanied by a more extensive atlas, arranged by temperature class, than that which accompanied Volume 1. Plate-taking on this program north of Dec. +30 0 is continuing with the new 100 prism on the Burrell Schmidt telescope recently relocated at Kitt Peak; these plans are discussed by Houk and Bidelman (25.114.167), and Williams and Houk (25.114.171) present some statistics on over 4000 peculiar HD stars in 15 categories. Bidelman (AstrJ 86, 553, 1981) has found 154 peculiar stars (HD and fainter) on 130 plates (Dec. 0 0 to _20 0 ) taken for the HD reclassification program and is searching a group of 54 similar plates along the southern galactic plane which are deeper than those previously surveyed by him. He will also do the "early result" search for astrophysically interesting stars on the new northern plates prior to Houk's HD classification. In other large proj ects, Stock continues his measures of the positions, radial velocities, classifications, and magnitudes of stars in an intermediate latitude zone (see 27.155.062, 2~ 031. 548) . h The catalogue now contains about 10,000 stars in the region R.A. 11 47 m to 15 23 m, Dec. _30 0 to _35 0 ; it will be published in the Rev. Mex. Astron. Astrophys. Bartaya (27.002.038) has presented a catalogue of types and luminosity classes for 10,396 stars in the Kapteyn areas 2 to 43 using the 70-cm Maksutov telescope at Abastumani; the dispersion is 166 R/mm at Hy. This work will be extended to SA 44-115 and to stars down to m 13. Henize, Wray, Parsons, and Benedict have presented a catalogue (25.002.067) ~f 500 stellar spectra in the wavelength region AA 1300-5000 taken during the 3 manned

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Skylab missions. The spectra have been measured and reduced to absolute fluxes; most of the stars are of type B. Henize, Wray, and Parsons (ApJ, in press) present a classification system for 0-B2 stars based on the resonance lines of CIV A1549 and SiIV AA1394, 1403. They find that the Si/C ratio discriminates well for luminosity in the 0 stars and for temperature among the 09-B2 stars of lower luminosity. Using Curtis Schmidt plates taken at the southern galactic pole by Slettebak, McNeil and Schiller have conducted surveys at 580 R/mm at Hy. McNeil (Bull. Amer. Astron. Soc. 13, 357, 1981) catalogued over 2200 G5-M stars to limiting magnitude V = 13.5 in an 81 square-degree region and used the data to discuss the percentage dwarf distribution with apparent magnitude and the space density distribution of giants to z = 2 kpc. Schiller (M.S. thesis, Ohio State University) surveyed plates covering 840 square degrees finding 183 M giants to limiting B-magnitude 14.5. Drilling and Landolt 0), or other even less conventional models. corres~onding

On the other hand, Huchra informs me that the Aaronson et al. calibration may still be uncertain by up to 30 percent, and Noerdlinger and Arigo (27.154.026) report that gravity diffusion of helium in old stars could conceivably lower the ages of globular clusters by about 22 percent from those of earlier models. In my judgment, the calibration of the extragalactic distance scale, as well as the theory of stellar structure, and especially of the radioactive dating of the elements over many Gyr are all uncertain enough that it is not yet established that there exists a problem with the age of the universe. There is a good recent review of the extragalactic distance scale by Hodge (1981). (b)

The decelepation papametep, qo'

A large amount of new redshift data has become available. In addition to magnitude-limited redshift surveys in selected regions of the sky (Section II), Hoessel, Gunn and Thuan (28.160.047) have now published redshifts for all Abell clusters of richness Class 1 or more, out to distance Class 4, and at galactic latitudes greater than 30°. At the other end of the scale, Spinrad (1981) now reports new optical redshifts for six clusters that range from z = 0.621 to

COSMOLOGY

637

z = 1.132; four of these are at z > 0.9. Nevertheless, our knowledge of the deceleration parameter has not significantly improved, partly because of subtle selection effects that enter in the determination of relative distances of remote clusters, but especially because of uncertainties in the evolution of galaxian magnitudes and colors. For example, Hoessel et al. attempt a formal solution for qo by comparing their data with Gunn and Oke's (13.162.005) sample of high redshift clusters, and find qo = - 0.55 ± 0.45, but with no correction for evolution. But using a completely different approach, Baldwin, Gaskell and Wampler have recently completed a long-term project to establish luminosity criteria in OSOs. They report that their study confirms that the C IV 1549 emission line is a useful "standard candle" in flat-spectrum OSOs. They are now observing C IV 1549 in low-redshift quasars with the IUE satellite to attempt a measure of qo. Preliminary results (without evolution) suggest qo - 1. (For a preliminary report, see Wampler 27.141.207.) If the standard hot big bang model is correct and if the observed deuterium is primordial, the observed ratio niH - 10- 5 points strongly to a low value of qo. A small deceleration parameter would also make it easier to reconcile the young age of the universe suggested by the recent large measures of Ho with the old ages implied by stellar evolution theory -- provided that all the uncertainties are in the right directions. Otherwise, the best, but still shaky, evidence for qo comes from determinations of the mean cosmic density, which appears to be too low by at least a factor of ten to close the universe. Neutrinos, if recent evidence that they may have non-zero rest mass turns out to be correct, could have a profound effect on the dynamics of stellar systems, and even on galaxy formation, but probably cannot contribute enough global density to affect significantly the evolution of the universe as a whole. (c)

Evidence fop gaZaxian evoZution

There are now good observational data on the counts of galaxies with increasing magnitude in widely separated areas of the sky, and most are in good agreement with each other. At the bright end, to about B = 20, are counts by Rainey (1977) and by Brown (26.158.148). Kron (28.158.072), Ellis (27.158.292), Peterson et al. (26.158.092), Karatchentzev (27.158.181, 27.158.291), and Tyson and Jarvis (25.158.171, 27.158.289) have all extended the counts to beyond J = 24 (Karatchenzev to B = 26 with an electronographic camera attached to the 6-m telescope). Kron's data show a larger number of galaxies near J = 24 than the others, which may be due to a different magnitude scale; Kron attempted to derive total magnitudes, while most other observers used isophotoal magnitudes. Now, the predicted numbermagnitude relation for galaxies is somewhat sensitive to K-corrections, slightly sensitive to the luminosity function assumed, and very insensitive to the choice of Friedmann models over a wide range of qo. These kinds of data are thus not useful in discriminating between cosmologies. On the other hand, the n(m) relation is very sensitive to evolution in magnitude or color (or both) of galaxies between the time of emission of their light (at moderate-to-Iarge redshift) and the present epoch, and thus the observation of n(m) provides our best hold on galaxian evolution. The most recent discussion of the interpretation of galaxy counts in terms of evolution is by Tinsley (28.151.051). She has calculated new evolutionary models based on an assumed distribution of galaxy types that make up a redder mixture of galaxies than in her earlier work. She finds that typically galaxies are about one magnitude brighter (in their rest frames) at z = 1.0 than at present. Her most rapidly evolving model shows a small hump in the galaxy distribution at J = 24, in qualitative agreement with a somewhat weaker feature in Kron's counts. The counts of the other observers do not show this "hump" (perhaps, as stated above, because of their definitions of magnitudes), but they do show evidence of slow evolution, and even this modest evolution can affect the value of qo found from the Hubble diagram by unity! Interestingly, Tinsley shows that Kron's counts are also compatible with

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the predictions of Barnothy's FIB cosmology, which demonstrates the problem of separating evolution effects from effects of adopting an entirely different, unconventional cosmology. REFERENCES Hodge, P W: 1981, Ann Rev A A 19, p. 357. Rainey, G W: 1977, Ph D Thesis, UCLA. Spinrad, H: (Reported by J J Puschell at I AU Sym 97, Albuquerque, NM).

II.

DYNAMICS AND STRUCTURE OF THE UNIVERSE

(a)

The LoeaZ SupepeZustep

The modern description of the Local Supercluster as a flattened aggregate of field galaxies, groups and small clusters, and centered near the Virgo cluster was first formulated by de Vaucouleurs (1953). The last several years have seen an accelerated interest in the system. The Shapley-Ames catalogue, most of whose entries are members of the Supercluster, has now been updated and revised (Sandage and Tammann 1981) and Yahil, Sandage and Tammann (28.158.225 and references therein) have used the new material to reanalyze the structure and kinematics of the Local Supercluster. The velocity field in the system has also been studied by Aaronson et al. (1981), and its geometrical structure has been rediscussed by Tully (1981). Tully finds 60 percent of the members of the Local Super cluster to be in a flat disk with diameter-to-thickness ratio of 6:1, and that the rms dimension of the short axis is ± 1.1 h- 1 Mpc (h = Ho/100 km s-l Mpc- 1 ). The remaining 40 percent of the galaxies form a "halo" structure of a few elongated clouds, with long axes more or less directed toward the center of the Supercluster. (Some of these same features seem to show on the Yahil et al. stereoscopic projections of the galaxies in the Revised Shapley-Ames Catalogue.) Tully concludes that either we see the disk at the moment of collapse, that there is a great amount of dark matter stabilizing it, or that the rms velocity perpendicular to the disk does not exceed 100 km s-l; the latter case would suggest that the Local Supercluster formed before its individual galaxies and groups condensed by dissipative processes. Yahil et al. find only a modest perturbation on the Hubble flow in the Local Super cluster (less than 200 km s-l), while the data of Aaronson et al. (Section I) indicate a somewhat larger peculiar velocity for the Local Group, consistent with the large-scale anisotropy of the background radiation, and also with a study by Joeveer (1981a) that shows the Hubble flow to be reduced by a factor of 1.45 in the Supercluster. Joeveer (1981b) also finds a group of galaxies in Virgo with a peculiar velocity of 300 km s-l with respect to nearby galaxies. The new kinematical study of Aaronson et al. (1981) proposes a model that takes into account deceleration of galaxies by the gravitation of the Local Supercluster. They find the velocity field to be compatible with general expansion of the system, but at a rate reduced from the general Hubble flow; they give a peculiar velocity toward Virgo of 331 km s-l. Their model, which is adjusted to minimize the scatter about the infrared Tully-Fisher relation, also has the Supercluster differentially rotating, with a velocity at the Local Group of 180 km s-l. It is interesting that this picture is very similar to conclusions reached by de Vaucouleurs at least 20 years ago.

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639

The disagreement between the various studies, however, suggests that the data are still open to too many variations in interpretation to reach a definite conclusion about the kinematics of the Local Supercluster. Nevertheless, there seems to be a consensus regarding its discrete nature, and most especially its considerable degree of flattening. (b)

Othep 8upepclu8tep8.

In addition to the Local Super cluster , more than a half-dozen other individual superclusters have been studied, some since about 1974. Recent investigations have included those by Ford et al. (1981) on two rich superclusters with mean redshifts of z = 0.12 and 0.14, each covering a linear extent of at least 50 h- 1 Mpc. Velocity data suggest that these great superclusters are nearly stable dynamically, and have probably evolved to near Hubble flow turnaround •. Comparison of the density of galaxies and clusters in the super clusters and in the surrounding fields leads the authors to conclude that a high enough cosmic density to close the universe is strongly excluded, and in particular that qo is less than 0.2. They do not, however, find that the observations suggest that their superclusters are flattened. In contrast, Einasto et al. (28.160.037), from their investigations of individual superclusters, find that chains of galaxies and.clusters are basic elements of superclusters, and that cluster chains (or sheets) comprise 50 percent of all galaxies; of the remainder, 30 percent of the galaxies are in poor chains and 20 percent are in the field. They report that the brightest cluster galaxies are ellipticals, with MB = - 22 (for Ho = 100 km s-l Mpc- 1 ), while the brightest in the field are spirals and irregulars with MB near - 19. The larger superclusters have diameters of about 50 Mpc, and the poorer chains from 15 to 20 Mpc. They find the chains to form a continuous network (albeit irregular), suggesting a cellular structure of the universe. Similar conclusions are reached by Corwin (1981) who has just completed an exhaustive study of a large supercluster in Indus. Einasto and Rees (1981) point out that the small (~ 100 km s-l) velocity dispersion that is typical among the systems within superclusters provides significant limitations on the process of their formations. At least since the Chincarini and Rood (17.160.031) study of the Coma/A1367 supercluster, it has been known that magnitude-limited redshift surveys show galaxies to be bunched up into limited regions in depth (superclusters) with large regions in between that are nearly or entirely devoid of galaxies. One of the more dramatic examples of this phenomenon has been demonstrated recently by Kirshner et al. (1981), who have done magnitude-limited redshift surveys in six fields in the northern and southern hemispheres. In three northern fields, mutually separated by about 35°, they have measured redshifts of 133 galaxies that comprise a sample at least 90 percent complete to R = 16. With reasonable assumptions about the galaxian luminosity function, they expected a peak in the number of galaxies with velocities near 16 000 km s-l; instead, they found a gap between 12 000 and 18 000 km s-l, which includes only one galaxy. This spatial gap seems to be at least 50 h- 1 across. In a continuation of their study, now in progress, they are examining about 100 additional fields within the triangle defined by the original three northern fields, and report (private communication) that evidence for the large gap seems to be holding up, although it is a far more complex structure than a single spherical void. D Weedman (private communication) has looked at all Markarian galaxies in the same region that have published redshifts (mostly in the Soviet literature). Of 113 such galaxies, he finds 12 with velocities in the range 12 000 to 18 000 km s-l, about as expected for a random distribution in depth. Because of the complex structure of superclusters and the expected intersupercluster regions, however, Weedman's findings are not necessarily in contradiction to those of Kirshner et al.

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Kirschner et al. also consider what density inhomogeneities are required at recombination to produce such large-scale inhomogeneities at the present epoch, and conclude that they should lead to velocity dispersions perpendicular to the main planes of superclusters that are typically only 150 km s-l, consistent with the value Tully finds for the Local Supercluster. Peebles (1981) calculates the evolution of density perturbations in an expanding Einstein-de Sitter universe consisting of concentric spherical shells, and arrives at a similar conclusion. In summary, the unequivocal results of recent studies are that large-scale structures exist in the universe on scales up to at least 50 h- 1 Mpc. Moreover, magnitude-limited redshift surveys show that most, if not all, visible matter is concentrated in these structures. The structures themselves -- superclusters -consist of a few rich clusters of galaxies, many groups and smaller clusters, and probably individual galaxies not associated with clusters and groups, but still within the superclusters. Most superclusters appear to be expanding, but there is strong evidence for gravitational perturbations on the global Hubble flow. The empty, or nearly empty, regions between superclusters have extents at least as great as those of the superclusters. There is suggestive evidence that some, but by no means conclusive evidence that all, super clusters are flattened systems consisting of chains and sheets of matter, and slight evidence that they may form an irregular spongy or honeycomb structure for the universe at large. The latter idea is hotly debated, however, and is crucial, for if correct i t would suggest that superclusters in the form of cells or Zel'dovich "pancakes" came first, with galaxies and clusters fragmenting later, while if galaxies came first and subsequently segregated into clusters and superclusters, the largest-scale inhomogeneities in the universe should be more or less individual entities. (c)

The mean aosmia density; possible pole of massive pelia neutpinos

There have been no recent major discoveries (except the possibility that neutrinos may have non-zero rest mass -- see below) of matter or objects that can contribute appreciably to the mean cosmic density. Estimates based on visible matter, e.g., by Abell (17.160.037), are generally heavily weighted by virial masses of rich clusters, within which any unseen matter (such as hot gas) is already included in the estimates of cosmic density. These estimates are typically of the order 10- 30 h 2 g cm- 3 , a factor of at least ten below the closure density. Estimates based on the dynamics of superclusters and on the assumption that superclusters are true density enhancements lead to similar results. Two recent experiments suggest that neutrinos may have a small rest mass. One of these (Reines, Sobel and Pasierb 1980) suggests that neutrinos alternate between different states or types (electron, muon, and tau), with a mass difference of the order of 1 eV/c 2 between the electron and either the muon or tau neutrino. The other experiment (Lyubimov et al. 1980) suggests that the beta decay of tritium indicates a neutrino rest mass in the range 14 to 46 eV/c 2 • The possible cosmological consequences of a non-rest mass for relic neutrinos was probably first discussed by Gerstein and Zel'dovich (1966). A number of papers has appeared recently, including those of Tremaine and Gunn (25.162.087), Doroshkevich et al. (28.162,013), Schram and Steigman (1981), Bisnovaty-Kogan and Novikov (28.162.058), Zel'dovich and Sunyaev (28.162.012) and others. For the conventional cosmological models the ratio of neucleons to photons is constrained by the observed abundance of deuterium and helium to be less than 4 x 10- 10 , which gives an upper limit to the nucleon density corresponding to n < 0.06, which is probably less than the density indicated by the dynamics of galaxies in clusters, and suggests that an appreciable part of the mass of the universe is not in nucleons (Schram and Steigman 1981). Neutrinos, if their rest mass is not zero, can provide that "missing mass." Neutrinos gravitationally clump

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with nucleons, however, if they become nonrelativistic at an early enough epoch, and the higher their rest mass, the earlier is that time. Neutrinos of rest mass near 20 eV/c 2 can collapse with large galaxies or binary galaxies and contribute to the massive halos now derived from galaxy dynamics (e.g., Faber and Gallagher 26.158.090). Those with mass less than 10 eV/c 2 cannot collapse with galaxies but can do so in clusters. Those with mass ( 3 eV/c 2 are unable to collapse even in the largest structures, but could still provide the dominant mass of the universe. Very massive neutrinos (~ 30 eV/c 2 ), on the other hand, should provide not only enough mass to close the universe but would result in an uncomfortably young age, unless A > 0 gr conventional cosmologies are wrong. As stated above, however, neutrinos of such high mass should collapse with galaxies where their dynamical effects are already taken into account, so that their contribution to the cosmic density would already be included in the density estimates given above. According to De R~jula and Glashow (28.162.105)~ muon neutrinos should decay and emit ultraviolet radiation, with half-lives - 10 4 s or longer. Recent analysis by Henry and Feldman (1981) of the Apollo 17 observations of the far ultraviolet flux from the direction of the Virgo cluster shows that even if the cluster's mass were entirely in neutrinos of rest mass in the range 16 to 20 eV/c 2 , their half-lives would have to be greater than 10 25 s. In any case, if neutrinos should turn out to have non-zero rest mass, they can play an important role in the evolution of the universe, and especially in the formation of galaxies and clusters. REFERENCES Aaronson, M, Huchra, J, Mould, J, and Schechter, P L: 1981, preprint. Corwin, H G: 1981, Thesis, U of Edinburgh. de Vaucouleurs, G: 1953, Astp J, 58, p 30. Einasto, J, and Rees, M: 1981, Natupe, in press. Ford, H C, Harms, R J, Ciardullo, R, and Bartko, F: 1981, Ap J, 245, p L53. Gershtein, S S, and Zel'dovich, Ya B: 1966, Sov Phys JETP Lett, 4, p 120. Henry, R C, and Feldman, P D: 1981, Phys Rev Lett, 47, p 618. Joeveer, M: 1981a, Astpofiaika, in press. 1981b, Astpofiaika, in press. Kirshner, R P, Oemler, A, Schecter, P L, and Shechtman, S A: 1981, Ap J, 248, p L57. Lyubimov, V A, Novikov, E G, Nozik, E G, Tretyakov, E F, and Kosik, V S: 1980, Phys Lett, 94B, p 266. Peebles, P J E: 1981, submitted to Ap J. Reines, F, Sobel, H, and Pasierb, E: 1980, Phys Rev Lett, 45, p 1307. Sandage, A R, and Tammann, G A: 1981, A Revised Shapley-Ames Catalogue of Bpight Galaxies (Wash. D C: Carnegie Institution of Washington). Schramm, D N, and Steigman, G: 1981, Ap J, 243, p 1. Tully, R B: 1981, U of Hawaii preprint.

III.

QUASISTELLAR OBJECTS AND RADIO SOURCE COUNTS

In a recent review Schmidt (1981) combines the results of faint surveys (e.g., Osmer 27.141.204) and that of Green (e.g., Schmidt and Green 27.141.203), to find an extremely steep increase in the numbers of QSOs with redshift, leading to estimates (for qo = 0) of 360 Gpc- 3 at z - 0, and 3 x 10 4 Gpc- 3 at z = 3. (By contrast, there are about 13 000 Seyfert galaxies per Gpc 3 at z _ 0.) Unless we are in the center of

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a spherically symmetric distribution of OSOs of radially increasing space density (in violation of the Copernican cosmological principle), their sharp increase must indicate cosmological distances and a strong luminosity evolution. QSOs could account for all the excess in the X-ray background from 3 keV to 300 keV, although such a conclusion cannot yet be verified because the QSO spectra are unknown at energies greater than 2 keV. There has still not been a single OSO found with z > 3.53, despite some surveys to B = 20.5, so a cutoff in their distribution above z > 3.5 is probably real. Further evidence that the redshifts of OSOs are cosmological and that they are active galactic nuclei is provided by a study by Wyckoff et al. (28.141.161), who have detected nebulosity around 3C273 out to a radial distance of 15", corresponding to a linear isophotal diameter of 90 kpc. The integrated red magnitude of the nebulosity (not including the quasar) is 16, corresponding to MR ~ - 25. In another study, Wyckoff et al. (1981) resolve similar nebulosity around 13 of 15 other OSOs. The nebulosities have isophotal diameters in the range 7" to 40", corresponding to a mean linear diameter of 90 ± 30 kpc. The mean integrated absolute red magnitude is MR = - 21.8 ± 0.8 (for Ho = 60 km s-l Mpc- 1 , and qo = 1). The "nebulosities" fit a Hubble law like that for galaxies, but 2 mag below the relation for m1 in rich clusters, and with aM = 3.0. The plausible conclusions are that OSOs are the nuclei of typical galaxies, but that the QSOs are more luminous, relative to their host galaxies, than are other active nuclei. Current studies of the ultraviolet radiation from OSOs by H E Smith, B T Soifer and others suggest that dust, although sometimes present, is not the dominant mechanism in determining the emission line intensity ratios in OSOs and in at least some Seyfert I galaxies. The observations support the hypothesis that the emission lines are formed in clouds that are very optically thick in the hydrogen lines. In a recent review, Cohen and Unwin (1981) report that of some 50 OSOs that have been mapped by VLBI, six (as of August 1981) have resolved features that show motions with "superluminal" velocities, ranging from 2.8 h- 1 to 10 h- 1 times c. The conventional explanation for the apparent super luminal speeds rests on a combination of fortuitous geometry and the finite speed of light, but even then relativistic ejection speeds are required, with Lorentz factors in the range 5 to 10, and the ejection must occur in a direction within, typically, 10° or 20° of the line of sight to the earth. With so few objects resolved, it is rather surprising that even six are observed with super luminal motions if the popular explanation is correct; at least, it would seem that most if not all OSOs eject matter at relativistic speeds. Zwicky (1937) suggested that galaxies, acting as gravitational lenses, should image background galaxies, and in his later life he often commented on his surprise that not even a single gravitational lens had been discovered. Subsequently, the Barnothys (1968) suggested the idea that OSOs might be gravitational lens events. Finally, the first probable gravitational lens has been found (Walsh et al. 25.141.094); that object, the double quasar 0957+561, has now been studied extensively, and appears to be actually several images of a distant quasar produced by a foreground cluster of galaxies. Roeder (27.158.325) showed that a transparent extended gravitational lens (as opposed to a point mass) must produce an odd number of images of a single source; in the modern models of 0957+561, the theory appears to be consistent with observations. Other likely gravitational lenses have been found since. In an interesting paper, Tyson (1981) uses the recent data on counts of galaxies with increasing magnitude to predict how many quasistellar objects might actually be enhanced images of early active nuclei galaxies, such as Seyferts, produced by gravitational lensing by intervening galaxies and clusters. He estimates K corrections for Seyfert galaxies and derives for the gradient of quasar counts with magnitude, d log NOSO/dm = 0.9, in agreement with present observations to 1Rth

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magnitude. The result is independent of lens model adjustable parameters, which directly affect only the absolute numbers of OSOs. Tyson finds that i f most OSOs to 18th magnitude are lens events, then an unreasonably large integrated mass of galaxies is required (Qgal > 1). On the other hand, it is an interesting possibility that a significant fraction of QSOs could be accounted for with this mechanism. I D Novikov (private communication) reports that the number, N, of sources as a function of the rate of radio flux, S, has been studied at A = 7.6 cm in the range 1 to 100 mJy with the RT-600 radio telescope in the Soviet Union. The log N - log S curve has a sharp slope at 1 mJy, contradicting earlier estimates made with statistical arguments. The behavior of the curve may be explained by either a rapid evolution of sources, or an approach to the "red horizon." REFERENCES Barnothy, J, and Barnothy, M F: 1968, Soienoe, 162, p 348. Cohen, M, and Unwin, S: 1981, presented at IAU Sym 97, Albuquerque, NM. Schmidt, M: 1981, presented at IAU Sym 97, Albuquerque, NM Tyson, J A: 1981, Ap. J, 248, p L89. Wyckoff, S, Wehinger, P A, and Gehren, T: 1~81, Ap J, 247, p 750. Zwicky, F: 1937, Phys Rev Lett, 51, p 290.

IV

COSMIC BACKGROUND RADIATION

There is still no definite detection of small-scale anisotropies in the cosmic background (3 K) radiation. I D Novikov (private communication) reports that the following upper limits have been obtained by observations with the RT-600 radio telescope:

Wavelength 7.6

cm

1.38 cm 2 cm

Angular Resolution 3' to 7'

IlT

T

10- 4 (near to 10- 5 )

7"

5 x 10-3

10"

5 x 10- 3

A large-scale dipole anisotropy, however, seems now to be well-established (Gorenstein and Smoot 1981; Fabbri et al. 27.066.306; Boughn et al. 1981). The combined data show a maximum of 3.78 ± 0.30 mK toward a = 11~6 ± 0~2; 6 = - 12° ± 5°. Boughn et al. also report a quadrapole component at the 4-0 level, whch they believe to be intrinsic, and Fabbri et al. report a "quadrapolelike" anisotropy as well. Their combined data suggest 6T/T ~ 3 x 10~5 at e = 6°, and 6T/T ~ 10- 4 at e = 90°. Peebles (1981) shows that such an anisotropy can result from gravitational potential gradients in an early universe with a fixed initial entropy per baryon number, even without large-scale mass fluctuations; indeed, he finds that the mass fluctuations need only be on a scale that would lead to the presently observed scale of clustering (~ 30 h- 1 Mpc).

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Richards and Woody (27.141.218) report what appear to be significant deviations of the cosmic background radiation from a blackbody spectrum, in the sense that the observed spectrum is more intense than a blackbody at the peak and less intense at higher frequencies; this distortion contains about 20 to 30 percent of the total energy. The observations of this deviation of the 3 K radiation from a perfect radiator are still in need of independent confirmation, but if real are difficult to account for by scattering mechanisms at a later epoch, which would be expected to heat rather than cool the radiation. Many authors, including Layzer and Hively (09.066.004), Rees (22.162.004), and Carr (1981) have thus suggested the possibility of creating the cosmic background radiation after the big bang, leading to a cold big bang in which formation of galaxies and stars is greatly facilitated. Although an early generation of stars (Population III) is easily produced, the difficulty is creating a near-blackbody spectrum. Rowen-Robinson et al. (26.162.026) and Wright (1981a) have suggested silicate dust heated by Population III stars at z - 200 to produce the excess radiation needed, but there are still difficulties in reproducing the long-wavelength tail. In a recent study, Wright (l981b) has found a solution witI'. a combination of Population III stars that burn from z = 300 to z = 134, and needle-shaped conducting dust grains; the total metal abundance required in this model is only Z - 10- 7 • In another study, Rana (1982) suggests that the microwave background radiation could be produced by thermalization of stellar and other radiation by long needle-shaped grains of graphite; in his model the thermalization ie of recent origin, at epochs of z - 10. REFERENCES Boughn, S P, Cheng, E S, and Wilkinson, D T: 1981, Ap J, 243, p L113. Carr, B J: 1981: MNRAS, 195, p 669. Gorenstein, M V, and Smoot, G F: 1981, Ap J, 244, p 361. Peebles, P J E: 1981, preprint of paper presented at the Vatican Study Week, on Fundamental Physics and Cosmology. Rana, N C: 1982, submitted to MNRAS. Wright, E L: 1981a, Ap J, in press. 1981b, preprint.

V.

COSMOLOGICAL MODELS

The conventional (Friedmann) evolving relativistic cosmologies with A = 0, combined with the "standard" model of the big bang, have achieved some remarkable success in predicting: 1) the expansion of the universe; 2) the correct (or nearly correct) H/He abundance ratio; and 3) the cosmic background radiation. A number of other observations are compatible with the conventional cosmologies, but are still to, uncertain to be regarded as confirming specific predictions or even providing a firm basis for the selection among possible Friedmann models; these include: 1) the shape of the Hubble law; 2) number counts of galaxies with magnitude, or of radio sources with flux; 3) number counts of galaxies or clusters with angular size; 4) D/H abundance ratio; 5) the mean cosmic density; 6) the possibility of massive relic neutrinos. Some observations, however, provide some problems with the conventional view, although none of these problems can yet be considered insurmountable. They include: 1) the short age implied by the most recent determinations of the Hubble constant, compared to those predicted by stellar structure theory; 2) the absence of observed small-scale anisotropies in the background radiation and consequent difficulty in understanding galaxy formation; 3) the deviations, if real, in the spectrum of the background radiation from that of a perfect radiator; 4) the large-scale isotropy of the universe, and problem of communication at t = 0; 5) the present excess of baryons over antibaryons (perhaps no longer much of a problem); 6) the unanswerable question about the nature of the universe at t < O.

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Perhaps these various problems along with the fact that abstract mathematical models are difficult to test (and hence eliminate), have been largely responsible for the considerable amount of work done recently in the field of theoretical cosmology. A number of such studies has been brought to my attention. It is difficult for me, as an observer, to evaluate all of them, but I shall at least attempt to summarize, or mention, a few. Particularly interesting results have been obtained from numerical simulation studies, such as those of Aarseth et al. (25.151.055 and 56) and Gott et al. (26.160.042), in which the behavior of from 1000 to 4000 point masses with random initial conditions, have been followed in expanding universes with n in the range 0.1 to 1. These simulations show that gravitational interactions between the masses result in a picture of clustering and superclustering that strongly resembles the present universe, and in particular produces a covariance function that is remarkably like that found from observation (e.g., Peebles and Growth 13.162.015). These simulations, however, do not in themselves account for the differences between the types of galaxies found within and outside rich clusters. Nor do they predict that most or all of the mass points assemble into sheets or "pancakes"; of course, it is by no means established that the "pancake" picture describes the real universe. McCrea and Rees organized a meeting of the Royal Astronomical Society in February 1979 to consider the problems of galaxy formation; a report of the meeting appears in the phiZ TPans Roy Soc London A, 296, pp 269-435, 1980. In particular, McCrea (1979) suggests that if sufficiently massive clouds of raw material of galaxies collide, a layer of shocked material is produced, which, with plausible parameters, breaks up into condensations with the masses of globular clusters. The primary condensations could produce high-mass, short-lived stars that soon explode, ejecting heavy elements for the production of the first "normal" stars. McCrea suggests that all original stars may have been so formed in globular clusters. The formation of primordial acoustic waves in the expanding universe, and their evolution near a singularity, have been considered by several Soviet cosmologists (Kompaneets et al. 1981; Lukash 1980; see also Mukhanov and Chibisov 1981). They propose that galaxies probably form from such waves, and consider the hypothesis that all physical modes of fluctuations have equal equipartition energies at to' The hypothesis leads to a new relation between the initial perturbation modes, and shows that an amplification of the potential perturbations near the singularity leads to a significant growth of the initial fluctuations, so that the initial amplitude of the perturbations can be less by orders of magnitude than was assumed previously. It has also been shown that the possibility of non-zero rest mass for neutrinos can have important effects on the processes of perturbation development and the formation of galaxies, improving the agreement between theory and observation (Bisnovatyi-Kogan, Lukash, and Novikov 28.162.057; Zel'dovich and Sunyaev 28.162.012; Doroshkevich et al. 28.061.002). Berstein and Shwartzman (1980) have derived the relation between the curvature and size of three-dimensional spaces with arbitrary topology. They find that for a constant negative curvature (k = - 1) the diameter of closed spaces is greater than 1.128 R, and for positive curvature (k = + 1) it is greater than 0.328 R, where R is the radius of curvature. The "simplest" model of the universe as a flat closed space (three-dimensional torus) is suggested, with all its parameters given in terms of atomic constants and current universal time. The total number of particles in this case is 2.87 x 10 76 , and the present diameter of the universe is 0.102 c H~1. Grishchuk and Zelmanov report on recent theoretical work at the Sternberg Astronomical Institute. Zelmanov (20.162.119) considered the Friedmann model with hyperbolic comoving space filled with dust-like matter (A = 0) in some non-comoving

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reference frames, and finds that in different frames of reference (including the comoving one) such features of the expanding (or contracting) universe as infiniteness or finiteness, the volume of space, the amount of mass, and the number of particles are not invariant, but are finite in some frames and infinite in others. The same is true of the age of the expanding universe. Spatial and temporal finiteness and infiniteness of the non-empty world is thus relative. Kharbedia (20.162.120, 22.162.009) has continued the work, and gives new examples of the relativity of spatial and temporal finiteness and infiniteness of some non-empty Friedmann models. Zalmanov and Kharbedia (21.162.009) have derived some necessary conditions for such relativities in the non-empty homogeneous isotropic cosmological models. Agakov (22.066.210; 1980; 1981) has found all homogeneous, stationary, rotating metrics that satisfy the Einstein field equations with the energy momentum tensor of a perfect fluid. He also considered the properties of solutions of the Einstein equations with a regular minimum of the scale factor of the comoving space, and investigated the behavior of the solutions near this regular minimum. Grishchuk and Popova (1981) and Grischuk and Polnarev (1980) have continued research on the physical processes in the very early universe and their possible consequences for its present structure. In particular, they show that modern theories of particle physics (namely, supergravity), as well as standard general relativity, admit the quantum process of graviton creation in the very strong gravitational field of the early universe. As a result the non thermal background of gravitational waves should exist now and in principle should be detectable. G.E. Tauber (private communication, 27 September 1981) reports that he finds time-dependent spherically-symmetric solutions of Einstein's field equations containing an arbitrary pressure and density distribution, which connects smoothly to a Friedmann universe for any desired equation of state. He matches the pressure at the boundary and finds conditions that limit the number of solutions to two. He suggests that these solutions may be applied to the description of lagging cores or initial inhomogeneities in the early universe. Davidson and McCrea (1981) have found an interesting development of Dirac's large number hypothesis (LNH). They show that if the LNH is assumed, then not only does the Newtonian gravitational constant decrease on an atomic time scale (G« t- l ), as inferred by Dirac, but the electrical force between two charged particles becomes stronger relative to their mutual gravitational force regardless of which of Dirac's two spacetime scales, atomic A or gravitational E (Einstein), is used. They conclude that the LNH implies an interesting reciprocity between atomic (or electrical) and gravitational phenomena in the A and E spacetimes, but it leaves open the problem of how to discuss simultaneously a combination of atomic and gravitational effects as they occur in the real world. Demaret (25.162.007, 28.162.009 and 92; 1980) and Demaret and Moncrief (28.066.070) have considered spatially homogeneous cosmological models of Bianchi types I, V, and IX, filled with a perfect fluid with an equation of state of the type p = (y - l)p (for values of y in the range 1 to 2). He finds the Bianchi models to be non-singular, in the sense that the quantum wave function becomes zero at the classical singularity. Such a model can be interpreted as a contracting universe bounding into an expanding one, due to quantum gravitational fluctuations. Among the more unconventional cosmologies is the G-varying cosmology of Hoyle and Narlikar. Narlikar and his associates have continued their study of the model (Canuto and Narlikar 27.162.006; Canuto et al. 1981; Narlikar and Rana 28.066.080) and argue that the model is con9istent with magnitude-redshift relation for galaxies, with the number-flux relation for radio sources, with the metric and isophotal angular size-redshift relation, and with the 3 K background. They further hold that it gives a better fit to the diffuse y-ray background than does the standard cosmology.

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Finally, Narlikar et al. say that the G-varying cosmology gives a better fit to the non-Planckian spectrum of the microwave background (as reported by Woody and Richards) than the standard cosmology. Also unconventional is the FIB cosmology of Barnothy and Barnothy. It is based on a perfect cosmological principle and a static Einstein universe. Time, length, and mass units of photons (and neutrinos) shift in relation to those of elementary particles; both the energy and wavelength of a photon increase exponentially with distance travelled, such that E and A are proportional to (1 + z)-I. The total energy in a beam of photons, however, is constant, so photons must decay (otherwise, their growing energy would increase the beam energy). Now, when ~E/E = ~A/A = 1.22, the spin of the photon goes from 1 to 1.5; then the photon decays into another photon of the same wavelength, but of spin 1, and a neutrino or antineutrino of spin 1/2. The photon thus loses 1/3 of its energy to a neutrino. Thus, after each such decay, the brightness of the source drops, which means that we would expect the number of sources as a function of redshift to show a periodicity with minima corresponding to steps in z of a factor 1.22. The Barnothys (1981) claim that 416 OSOs in seven complete samples show just this effect, as do 869 OSOs in another collection of incomplete samples. Still another cosmology is the chronometric one of Segal. In this model the universe is closed and static, and the redshifts are due to "aging" of light. One of the predictions of the model is a quadratic, rather than linear, Hubble law. In a number of recent papers (e.g., Segal 1979, 28.158.020; Segal and Segal 28.162.033); Nicoll and Segal 27.031.520; Nicoll et al. 1980), Segal and his collaborators present elegant arguments based on statistics of bright galaxies and on quasars to show that the quadratic law provides the closer'fit to the observations. Most observers, however, find the case unconvincing, especially in view of the very tight Hubble relation for first-ranked cluster galaxies, and they prefer to interpret the excess of large redshift OSOs as an evolutionary effect. One of the most exciting areas of modern cosmology, albeit one of the most speculative, concerns the relation between conditions of the very early universe and the nature of fundamental particles and forces. This union of theoretical physics and astrophysics at the earliest instant of time has resulted in the development of the g~nd unified theopies (GUTs). There is a recent review by Zel'dovich (1981). There was also a special conference sponsored by the National Science Foundation, "The Interaction of Particle Physics and Astrophysics," held in May, 1981, at the Institute of Theoretical Physics, University of California, Santa Barbara. There are no formal proceedings of that conference, but a summary, entitled "The Early Universe," has been prepared by Kolb and Turner (1981). REFERENCES 1980, Vestnik Mosk U, Sep 3, Fiz, astpon, No.2, 21, p. 80. 1981, ibid, No 2, 22, p 49. Barnothy, J M, and Barnothy, M F: 1981, BAAS, 12, p 852. Berstein, I Nand Shgwartzman, V F: 1980: ZhETF, 79, p 1617 & p 1628. Canuto V M, Owen, J R, and Narlikar, J V: 1981, A & A, 92, p 26. Davidson, W, and McCrea, W H: 1981, Ppoe R Soe Lond, A, 374, p 447. Demaret, J: 1980, BuZZ Aead R BeZgique, 66, p 473. Grishchuk, L P, and Polnarev, A G: t980, in CenepaZ ReZativity and Cpavitation, 100 Yeaps Aftep the Bipth of Einstein (ed A Held). Grishchuk, L P, and Popova, A D: 1981, Sov Phys JETP, ZET Ph, 80, No 1. Kolb, E Wand Turner, M S: 1981, Natupe, in press. Kompaneets, D A, Lukash, V N, and Novikov, I D: 1981, preprint, Spaee Reseapeh Agakov, V G:

Institute, USSR Aead Sei. 1980, Pisma ZhETF, 31, p 631.

Lukash, V N:

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REFERENCES

(Continued)

McCrea, W H: 1979, I"I'ish Ast"l' ,7. 14, P 41. Mukhanov, V F, and Chibisov, G V: 1981, preprint FIAN. Micholl, J F, Johnson, D, Segal, I E, and Segal, W: 1980, P"I'oe NatZ Aead Sei USA. 77, p6275.

Segal, I: 1979, P"l'oe NatZ Aead Sei USA. 77, p 10. Zel'dovich, YaB: 1981, Nauk. 133, p 479.

G.O. ABELL President of the Commission

48. HIGH ENERGY ASTROPHYSICS (ASTROPHYSIQUE DE GRANDE ENERGIE)

PRESIDENT: F. Pacini VICE-PRESIDENT: R. Giacconi ORGANISING COMMITTEE: J. Audouze, J.L. Culhane, K.I. Kellermann, E.N. Parker, E.E. Salpeter, I. Shklovski, J. Trumper In view of the broad range of topics covered by Commission 48 and the consequent inevitable overlap with other commissions, it is not feasible to produce a comprehensive self-contained report. The commission therefore restricts its report to a selected list of accessible recent review articles and conference reports, where up-to-date summaries of various topics can be found. Such a list is given below. A.

REVIEW ARTICLES Baym, G. & Pethick, C.: Astrophys. 17

1979, Physics of Neutron Stars, Ann. Rev. Astron.

Cesarski, C.: 1980, Cosmic-Ray Confinement in the Galaxy, Ann. Rev. Astron. Astrophys. 18 Culhane, J.L.:

1981, Extragalactic X-Ray Astronomy Science Progress 67, p. 223

Dolgov, A. & Zel'dovich, Ya.B.: Rev. Mod. Phys. 53, p. 1

1981, Cosmology and Elementary Particles,

Kellermann, K.I. & Pauliny-Toth, I.: Astron. Astrophys. 19.

1981, Compact Radio Sources Ann. Rev.

Lewin, W. & Joss, P.: 1981, X-Ray Bursters and the X-Ray Sources of the Galactic Bulge Space Science Rev. 28 Miley, G.: 1980, The Structure of Extended Extragalactic Radio Sources, Ann. Rev. Astron. Astrophys. 18 B.

CONFERENCE PROCEEDINGS Proc. IAU Symposium No. 94 "Origin of Cosmic Rays" (Bologna 1980) Proc. IAU Symposium No. 95 "Pulsars" (Bonn 1980) Proc. IAU Symposium No. 99 "Extragalctic Radio Sources" (Albuquerque 1981) Proc. Royal Astron. Society Meeting "Gamma Ray Astronomy" (London 1980) Proc. Uhuru Memorial Symposium, Washington Academy of Sciences (Washington 1980) Proc. 17th Cosmic Ray Conference IUPAP (Paris 1981) Proc. 9th Texas Meeting on Relativistic Astrophysics Optical Sets in, Galaxies ESA-ESO Workshop 1981

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49:

THE INTERPLANETARY PLASMA AND THE HELIOSPHERE (PLASMA INTERPLANETAIRE ET L'HELIOSPHERE)

PRESIDENT: H.J. Fahr VICE-PRESIDENT: I.W. Roxburgh ORGANIZING COM}1ITTEE: J.L. Bertaux, S. Cuperman, A.Z. Dolginov, S. Grzedzielski, H.U. Keller, F. Paresce, C.S. Weller I.

INTRODUCTION

This commission is intended to study the following problems: (1) the solar corona, i.e. the region of the origin of the solar wind; (2) the heliosphere, i.e. the region dominated by the supersonic solar wind as it expands through the neutral component of the interstellar medium; (3) the heliospheric interface, i.e. the region in which the interaction between the two counterstreaming magnetized plasmas, the subsonic solar wind and the interstellar medium, takes place. The activities of this commission cover both theoretical and observational investigations of these three regions. In the following presentation members of this commission will give status reports with concern to ongoing investigations in the aforementioned scientific fields of this commission. II.

BASIC RESULTS OBTAINED IN THE USSR DURING 1979-1981 WITH CONCERN TO COMMISSION 49 (INTERPLANETARY SPACE) (A. Z. Dolginov) A.

Solar Wind Plasma Studies

The study of the solar wind plasma via measurements performed in 1979-1981 by means of broad-angle instruments on board the Earth satellites Prognoz 4 and 6 was continued. Physical processes in interplanetary space connected with the propagation of the shock waves generated by the solar flare on January I, 1978 were investigated by means of complex measurements of plasma, magnetic field and energetic particles performed aboard the Soviet space probe Prognoz 6 and the West German space probes Helios I and 2 at three different points in the solar system. The interplanetary shock wave was observed as a "piston wave" on Helios I and as a "blast wave" on Helios 2 and Prognoz 6. This result demonstrated the absence of a direct relation between the characteristics of the interplanetary shock wave and the time of energy release on the Sun. It seems that there are no pure "blast waves" at all. Such waves are registered only if the point of observation is inappropriately connected by the magnetic lines with the point of the flare. The possibility of proton acceleration up to the energy of several MeV in the oblique shock waves during the time of the order of I min (shock-spike) was shown. An essential increase of proton flux with the energy 1,4-5,8 MeV observed aboard the Prognoz 6 satellite in the vicinity of the oblique shock wave front is evidence for an acceleration process in such waves. There is up to now no theoretical explanation for this effect. The study of plasma characteristics and electron spectra at energies of about 1 MeV with Prognoz 4 shows that the source of electrons in the region near the magnetopause is the same as considered by Meng and Anderson (1970). The essential difference of the electron flux behaviour in different magnetospheric regions shows that the source of electrons is the outer radiation belt on the dayside of the magnetosphere. A model of the system of currents in the vicinity of Venus is proposed. It is based on the measurements of plasma and electron fluxes performed aboard the Venus satellites Venera 9 and 10. 651

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References Gringauz, K.1., Kurt, V.G. et al.: 1980, "The January 3, 1978 event: an example of shock acceleration in interplanetary space", report at VIII MPAE - Lindau Workshop on acceleration of particles by shock waves throughout interplanetary and interstellar space, Katlenburg-Lindau, FRG, October 1980. Kurt, V.G., Stolpovsky, V.G. et al.: 1980, "Energetic particle solar wind plasma and magnetic measurements by Prognoz 6 during the large scale interplanetary disturbance of Jan. 3-4, 1978", preprint KFKI-1980-32, Central Research Institute for Physics, Budapest. Mineev, Yu. V., Spirkova, E.S. et al.: 1980, "Prognoz 4 observations of electrons accelerated up to energies of 2 MeV and of the cold plasma between the magnetopause and the bow shock", preprint KFKI-1980-29. Gringauz, K.I., Verigin, M.I. et al.: 1979, J. Geophys. Res. 84, 2123. Gringauz, K.1., Verigin, M.1. et al.: 1979, "Low energetic electrons in the Venus optical umbra detected by Venera 9 and 10 - the source of the night ionosphere. Comparison with the Pioneer-Venus satellite measurements", preprint Pr-534, Space Research Institute, Moscow. Gringauz, K.I.: 1981, Adv. Space Res. 1, 5, Cospar 1981. B.

Solar Cosmic Rays

A study of solar cosmic rays was continued in 1979-1980 by the Prognoz satellites and the Venera space probes. Proton acceleration has been shown to take place in all cases where the electrons are also accelerated, even in the faintest flares at a small total energy release in the absence of a second acceleration stage in the shock wave. The energy loss by particles during their propagation in interplanetary space, resulting in a falloff of the spectrum in the low energy range, has been studied. The inclusion of such a loss has made it possible to derive the same altitude of generation for protons as for electrons. The gamma ray emission from solar flares has been studied theoretically. The nuclear reactions of the flare-accelerated heavy nuclei have been shown to contribute much to the gamma ray flux. For example, if particles are accelerated in a flare up to rather small energies below 10 MeV/nucleon, then all the gamma rays will be produced in the nuclear reactions of heavy nuclei. References Kurt, V.G., Logachev, Yu.I. et al.: 1979, Izv. Acad. Nauk SSSR ser. fiz. 43, 3519. Kurt, V. G., Logachev, Yu.1. et al.: "Energetic solar particle spectra according to Venera 11 and 12 and Prognoz 5 and 6 measurements", Proc. 17th ICKC, Paris 1981, Paper SN2, 1-11. Kuzhevsky, B.M.: "Some consequences of the application of solar gamma astronomy to solar cosmic ray studies", Provo Vllth European Symp. on Cosmic Rays, Leningrad, 1980, p. 263.

c.

Solar Wind Plasma Turbulence

A method to map the interplanetary plasma turbulence based on the scintillation index for more than 150 sources per day was elaborated. The following results have been obtained in observations carried out in 1975-79: a) the polar regions of the interplanetary plasma are essentially perturbed during the solar activity cycle (in the years of the activity solar maximum the structure of the interplanetary plasma has a quasi-spherical symmetry, in the years of the activity minimum it is elongated in the equatorial direction); b) there exists a strong correlation (the correlation coefficient reaches 0,75) between the scintillation index averaged over all sources and the geomagnetic A index. p

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References Vlasov, V.I., Chashey, I.V. et al.: 1979, Geomag. and Aeron. 19, 401. Vlasov, V.I.: 1981, Geomag. and Aeron. 21, No.3; Preprint, FIAN kg 161, 1979. Shishov, V.I., Vlasov, V.I. et al.: 1981, Geomag. and Aeron. 21, No.5. D.

Radio Scintillations

A theory of nebular radio source scintillations was elaborated. The statistics of scintillations indicates the discontinuity structure of the solar wind which consists of many jets. The velocity distribution of the interplanetary plasma was obtained. The possibility of geomagnetic activity predictions using scintillation data has been considered. References Lotova, N.A. and Chashey, I.V.: 1980, Astron. J. USSR 57, 328. Blums, D.F. and Lotova, N.A.: 1981, Geomag. and Aeron. 21, 209. Lotova, N.A. and Chashey, I.V.: 1981, Geomag. and Aeron. 21, 435. Blums, D.F. and Lotova, N.A.: 1981, Geomag. and Aeron. 21, 9, Lotova, N.A. and Blums, D.F.: 1980, Geomag. and Aeron. 20, 1124. Blums, D.F. and Lotova, N.A.: 1981, Geomag. and Aeron. 21, 178. E.

Particle Acceleration

A theoretical analysis of solar cosmic ray propagation and acceleration by shock waves in the interplanetary medium was developed. The explanation of the temporary and spectral features of cosmic ray observation was put forward. Charged particle adiabatic invariants for an oblique shock wave field have been considered on the basis of the Krylov-Bogolubov asymptotic method. The energy gain of fast particles has been calculated. A theory of cosmic ray acceleration by weak solar flares was developed. The abundance anomaly (He 3 and heavy elements) was explained. A general consideration of events which accompany the events in radio, X-ray and optical bands was performed. A theory of MHD waves in an inhomogeneous and moving medium has been developed. Nonlinear effects and destruction of the waves have been considered. The theory has been applied to the MHD wave evolution in the interplanetary medium. Some abrupt interplanetary magnetic field intensity variations observed aboard the spacecrafts at the heliocentric distance from 0.3 to 2.2 AU are explained by the heliographic longitudinal dependence of solar wind flow. An analysis of the observational results proves the existence of a large extension of the corotating streams. The discrepancy of the magnetic field intensities, obtained at various heliocentric distances, with those predicted by Parker's model is explained as a result of some solar magnetic field variation. References Toptyghin, I.N.: 1980, Space Sci. Rev. 26, 157. Bykov, A.M., and Toptyghin, I.N.: Izv. AN SSSR ser. fiz. 44, No. 12, 1980; 45, No.4, 1981. Ganov, S.P. and Toptyghin, I.N.: 1979, Radiofizica 22, No.4. Vasil'jev, V.N. and Chirkov, A.G.: 1981, Izv. AN SSSR ser fiz. 45, No.4. Kocharov, L.G.: 1980, Izv. AN SSSR ser. fiz. 44, No. 12. Dolginov, A.Z. and Muslimov, A.G.: "Correlation of the interplanetary magnetic field enhancements with the solar wind velocity variations".

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III.

FREE NEUTRALS IN INTERPLANETARY SPACE: SOURCES AND COUPLING TO THE SOLAR WIND PLASMA (S. Grzedzielski) A.

Introductory Remarks

This report deals with the problems related to the presence of free neutral atoms (molecules) in interplanetary space. The scope of the subject was substantially broadened in recent years as in situ measurements based on direct counting of energetic neutrals or on indirect analysis of plasma signature variations ascribed to neutrals (and dust) began to supplement the classical optical (Lv) detection methods. The new important Voyager results are discussed in somewhat greater detail. The point sources of neutral gases in the Solar System include terrestrial planets, comets, Jupiter (10), Saturn (Titan), and as a possible candidate (although not confirmed as yet) the Sun. The extended sources consist of the all-pervading neutral interstellar wind and, possibly, the interplanetary dust. Excluded from the present report are the terrestrial planets and the comets. Although, at least in the case of Venus, copious fluxes of neutrals seem to penetrate into the solar wind well ahead of the planet, in both of these types of objects the emission of neutrals is intimately linked with the structure of their ionospheres/exospheres. Neutral fluxes ahead of even the bow shock may also be a typical feature of active comets at heliocentric distances ~ 3 AU. This issue will hopefully be elucidated during the planned missions to the Halley comet (encounter in March 1986). B.

Jupiter and Saturn as Sources of Neutrals

The Pioneer and Voyager data together with the Earth-based (visual) and Earthorbiting (mainly UV; Copernicus, IUE) spectroscopic observations indicate that the systems of Jupiter and Saturn may leak free neutrals to the interplanetary space. With the energy per particle less than 0.01 eV in the atmospheres of Jupiter and Saturn no direct escape seems possible (Trafton, 1981). However, the energetics of escape from 10 and (possibly) Titan looks much more promising (Cheng, 1980; Dessler, 1980; Eviatar and Siscoe, 1980; Pollack and Witteborn, 1980; Shemansky, 1980; Smyth, 1981; Trafton, 1981). Enhanced sputtering rates for the icy satellites (Johnson et aI., 1981) may also contribute to the production of neutrals. The neutral H cloud associated with Titan (Barker et al., 1980; Broadfoot et aI., 1981a; Clarke et aI., 1981; Judge et aI., 1980; Sittler et al. 1981) extends probably from 8 to 25 Saturn radii and may contain up to 2 x 10 34 neutral H atoms (Broadfoot et al., 1981 a). Also dust and neutrals seem to be present in the E-ring region (Sittler et al., 1981). For most of the time the Titan torus is probably contained within the magnetosphere of Saturn (Bridge et al., 1981), and the H atoms, if ionized by (mainly) electron impact, will have little chance of escaping. On the other hand, charge exchange with the radiation belt protons may lead to high energy neutrals. During the approach of Voyager 1 to Saturn such neutrals (of energy exceeding 40 keV) seem indeed to have been observed (Kirsch et al., 1981b; also Stone and Miner, 1981). The estimated loss rate is ~1024 neutrals/so At times of enhanced solar wind pressure part of the cloud may extend out of the magnetosphere (Pioneer 11 flyby, Wolfe et aI., 1980; also Sittler et aI., 1981) and H may charge-exchange with the solar wind magnetosheath. If, for instance, Titan happened to be exposed to the magnetosheath protons for 1/4 of its orbit (; 3.4 x 105 s), ~1030 neutral H atoms of ~1 keV energy could be produced (rate 3 x 10 24 at./s). 10 can be a much stronger and permanent source of neutrals. Several escape mechanisms from the 10 surface/atmosphere were proposed: volcanic activity (plumes), Jeans' escape (also via the Lagrange point), exobase exposure to the Jupiter magnetospheric plasma, sputtering of surface and/or atmosphere (Pollack and l~itteborn, 1980; also Cheng, 1980; McElroy and Young, 1975; Smith et aI., 1979 Haft et al., 1981). Loss rates spanning 5 orders of magnitude, up to 10 8 g/s (;10 3 S02molecules/s)

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are being suggested (Cheng, 1980; also Haff and Watson, 1981), although the estimates (of eventual ion supply) based on mass loading of the 10 plasma torus point towards rather lower values of 10 28 ions/s, and the (model dep~ndent) estimates inferred from the intensity of the observed 0 and S emission lines yield 10 27 ions/s (Shemansky, 1980; Broadfoot et aI., 1981b; Brown and Ip, 1981). The escaping neutrals (S02' SO and then Sand 0) move in the 10 torus with the Keplerian velocity (17 km/s)~and~are upon ionization (mostly by the low energy electrons) picked up by the v x B electric field of the corotating Jovian magnetosphere (corotation speed = 74 km/s at 10). Hence they acquire cyclotron gyration energies of up to 90 eV/nucleon. A subsequent charge exchange of such an ion with a torus neutral creates neutral atoms of energies ranging up to 1.5 keV for the o atoms. Such energization associated with the intramagnetopause rather than with the bow shock phenomena is also suggested by the Voyager I and 2 observations of heavy ions (Zwickl et al., 1980). Dissociative attachment of < 10 keV electrons on S02 may even lead to higher energies: the reaction products (S and 0 atoms) are left with a small additional energy that allows them to climb ballistically up in the gravitational field of Jupiter. They may then charge exchange in regions with higher corotational velocities. Thus neutrals with energy ranges of tens-of-keV can be produced. Only a very tiny fraction of all 10 neutrals may be involved in this last process (Cheng, 1980). Such very energetic neutrals (14 - 61 keV) could have possibly been detected by Voyager I during the approach to Jupiter (230 - 100 Jovian radii from the planet, Kirsch et al.~ 198Ia). The inferred total neutral loss rate by Jupiter is (if isotropic) ~ IOL5 at./s. Since the bulk of Jovian neutrals will rather have energies < I keV, the reported neutral flux does not necessarily contradict the high loss rate (~1030 at./s) favoured by Cheng. Adopting this high rate both for 0 and S escaping isotropically with ~80 km/s (at infinity) one obtains that the 10 neutrals may dominate (by mass) over the neutrals of interstellar origin within 1/4 AU from the planet. In this case the mass loading of the solar wind by the Jovian neutrals (ionization time = 2.7 x 10 7 s at Jupiter orbit) may slow down the solar wind by ~1.5 km/s upon arriving at 60 Jovian radii from the planet (expected solar wind ion temperature increase ~ 3000 K). The production of neutrals, if depending on the volcanoes, may also be a strongly time-dependent phenomenon (Cheng, 1980). In any case variations in the 10 torus are observed (Sandel et aI., 1979; Warwick et aI., 1979). C.

Outgassing from the Interplanetary Dust

For an interplanetary grain saturated with the solar wind particles, which seems to be the case for the inner solar system, the desorption of neutrals will keep pace with the impinging ion flux (Holzer, 1977). Beyond a few AU from the Sun the amount of dust seems to be too small (Stanley et aI., 1979) to yield a measurable effect unless there exist in these regions some unknown sources of fine dust grains. One such possibility was recently put forward by Mendis et aI. (1981): beyond 5 AU from the Sun submicron grains can be electrostatically levitated and removed from the cometary nuclei, yielding a dust blow-off rate comparable to that observed in medium bright comets during perihelion passage between 3 AU and 0.5 AU. However, the best known and most promising dust source is the outer part (r > 4 solar radii) of the circumsolar dust cloud (Leinert et al., 1978; Beard, 1979; Mukai and Yamamoto, 1979) in which the suhlimation rate may still be low enough to enable the magnetite dust to survive (Mukai and Schwehm, 1981). The production of neutrals by dust outgassing in that region was investigated by Fahr et al. (1981) for a model distribution of dust grains based on the Helios data (Leinert et al., 1978). The erosion rate seems to be sufficiently small to virtually ensure all hydrogen to desorb as H2' 5% of which is subsequently dissociated into H atoms. However, desorption as SiH or CH with an 80% recovery of atomic H by subsequent dissociation is also under discussion (Fahr et al., 1982). Helium will appear in atomic form. As the thermal speeds of the dust-generated neutrals are small compared to the (circular) orbital velocities of the parent grains, the resulting density of neutrals will essentially be determined by the local (very fast) ionization

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rate compensating the local production of neutrals. For a plausible value of the dust density parameter r = 2 x 10- 19 cm- I Fahr et al. (1981) obtain nH",IO- 2 at./cm3 (nHe'" 10- 3 at. fcm3 ) at 4 solar radii. Charge exchange of the outgassed neutrals with the solar wind protons will constitute a source of I keV H atoms and also (after "pick up") of keVfnucleon He+ and H+ ions that do not exist in the primary solar wind. The dust-generated neutral cloud should shine in the resonantly scattered solar Ly-a and He-584 A lines. These emissions could be within the reach of observational capabilities for look angles close to the Sun «6 0 ) if the above value for r is realistic (Fahr et al., 1981). However, r could as well be much smaller and the intensity varies directly with r. Also complicated dust grain dynamics (Morfill and Grlin, 1979) could alter the calculated intensity spectra. D.

Neutrals of Interstellar Origin

The external local interstellar medium constitutes by far the strongest source of neutrals to the interplanetary space. Assuming a 100 AU heliosphere radius, a 20 km/s inflow velocity, and 0.05 atoms/cm3 neutral external density, the source strength is ~7 x 1035 at./s. Almost all information on these neutrals is obtained by analyzing the scattered solar H I Ly-a and He I A584A lines. Recently, first H I Ly-B measurements were reported (Shemansky et al., 1979); also the reality of a previously reported absorption feature in the solar spectrum and attributed to neutral H was assessed (negative conclusion, Meier, 1979; Artzner et al., 1981). The general picture is rather well understood (Fahr, 1974; Holzer, 1977; Thomas, 1978). In recent years the data are interpreted in terms of the so-called "hot" (Meier, 1977; Wu and Judge, 1980) model which describes how an initially isotropic and Maxwellian velocity distribution of neutrals changes when it is convected towards and then "falls" into the gravitational well of the Sun (Danby and Carom, 1957) with a net loss of particles due to ionization (Meier, 1977; Fahr, 1978). The salient features of the distribution of neutrals are a large cavity for H and a smaller one for He accompanied by a very long island of increased He density as a result of gravitational focusing. Recent successes in the investigation of interplanetary resonance radiation at 1216 A and at 584 A are reviewed in the contribution following this report. E.

Coupling of the Newly ·Ionized Particles to the Solar Plasma

The ionization proceSRes do not practically alter the momentum of a neutral atom undergoing ionization. The newly ionized particles (new ions) inherit the velocity distribution function characteristic for the parent neutrals. Two problems arise: (I) will (and on what time scale) the velocity distribution function of the new ions "relax" to the distribution function of the background plasma?, and (2) if yes, will this then significantly affect the general state of the solar wind? A positive answer to (I) was given almost a decade ago for a-type distribution functions of the neutrals in a series of papers by R.C. Davidson, R.E. Hartle and C.S. Wu. The time scales were short compared to the flow time scales of the solar wind. Recently the problem was discussed again by Curtis (in the context of the Venus exosphere, 1981) and Grzedzielski and Rozmus (1982) for a more realistic case of finite temperatures of the new ions. Again the time scales proved to be short: for an equilibrium situation (production of new ions by ionization compensated by their loss through particle-unstable wave interaction) the relaxation time scales on a linear theory are between 102 s (at ~I AU) and loS s (at ~100 AU) both for hydrogen and helium. The number density of the "unrelaxed" new ion population is then between ~lcr6and ~10-9 cm- 3 . The theoretical short time scales may possibly be in conflict with an observational datum on the He+ ions: as shown by Paresce et al. (1981) an upper limit for the interplanetary He II A 304 A emission can be used to set a lower limit of 109 s for the decrease of the suprathermal He+ velocity towards the bulk solar wind speed. The rare occurrences of the He+ ions being detected in the interplanetary shock waves are attributed to traces of "cold" chromospheric plasma carried away by the flare ejecta (Schwenn et al., 1980; Gosling et al., 1980)'.

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If the short time scales do apply, one can treat (2) in terms of fluid dynamics (in any case the mass loading in a direction perpendicular to the magnetic field is rather beyond doubt). The dust-generated neutrals do not significantly affect the solar wind flow (Ripken and Fahr, 1980; Fahr et al., 1981). A measurable effect, even at moderate solar distances, can probably result from the solar wind being slightly decelerated, heated-up and deflected by the downwind helium island (Grzedzielski, 1980). However, the solar wind can be influenced by the mass loading of neutrals, especially at large heliocentric distances, and the predicted deceleration and heating of the solar wind plasma can in the future be tested against the measurements: as estimated by Bteszynski and Grzedzielski (1982), the expected solar wind velocity gradient at the positions of Pioneer 10 in 1986 and Voyager 1 in 1989 will be 5 km/s per 10 AU. Petelski et al. (1980a, 1980b) have discussed the fluid-like interaction of the solar wind with the interstellar neutrals (on the stagnation line only) when the ionization rate is increased by the so-called critical velocity effect (observed in the laboratory when the energy of the bulk motion of the neutrals relative to the background plasma exceeds the ionization energy). By scaling up the laboratory results to the interplanetary conditions, a significant enhancement of ionization is obtained for heliocentric distances ~ 10 AU. However, the exceedingly long growth time scale for the "turbulent heating" of the ionizing electrons may raise doubts as to the legitimacy of the scaling over so vast a gap of values. Assuming the approach to be valid, Petelski et al. obtain a much more rapid deceleration of the solar wind, and the terminating shock becomes very weak or non-existent (cf. also Petelski, 1981) with the heliosphere radius significantly diminished. The neutral interstellar atoms were also suggested to be the source of the so-called "anomalous" component of the cosmic rays (enhanced He, N, 0, Ne at ~10 MeV/nucleon, Fisk et al., 1974; Fisk, 1976). These atoms, upon ionization in the solar cavity, may then be swept back to the outer heliosphere and accelerated on the way to ~10 MeV/nucleon. Then, having high rigidities now (single ionization!) they easily diffuse back again into the inner heliosphere. The recent intercomparison of the Helios 1 and 2 and Pioneer 10 cosmic ray data (McDonald et al., 1981) indicates that near solar maximum most of the modulation must occur beyond 23 AU, and that the "anomalous" and galactic cosmic ray helium intensities are well correlated. This suggests that the required interplanetary acceleration of the "anomalous" component probably occurs beyond the modulation region. The discussion of the modulation data (especially for the high energy particles) is hindered by the poorly understood role of large-scale drifts (Fisk, 1981) and the dependence of modulation on the changes of "waviness" of the interplanetary current sheet (Jokipii and Thomas, 1981). F.

Neutral Species and the Boundary of the Heliosphere

If one assumes that the temperature of the ionized component of 1ISM (local interstellar medium) is ~104 OK as deduced from the analysis of neutral gases, then the Mach number M of the interstellar gas flow past the heliosphere is ~ 1. The heliosphere then must be compressed in the upwind direction, with the ionized component deflected around the flanks and the neutral· component going (almost) directly inside. Even in the simplest case of a fluid-like description of the solar wind plasma ramming against the interstellar plasma, the problem is difficult. The boundary values have to be stated on surfaces (inner shock, tangential discontinuity, outer shock) that depend on the solutions themselves. This difficulty was circurnr vented by Baranov et al. (1979) by finding the stationary solution as an asymptotic case of the non-stationary ones. Knowing the plasma flow between the surfaces, Baranov et al. are able to estimate the relative number of the primary interstellar H atoms that go through unaffected by charge exchange with the deflected interstellar plasma (the analysis wa; also extended to the case when the force upon the deflected flow due to momentum transfer from 1ISM by charge exchange with interstellar neutral hydrogen is taken into account, Baranov et al., 1981).

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These results bear on the discussion of the intriguing question of the anomalous observed H/He ratio (cf. Part IV). Assuming that the standard ratio 10 holds in LISM, two (extreme) views can be proposed: (a) the observed ratio is ~5 instead of 10 because H in LISM is ~50% thermally ionized while He stays neutral. This agrees nicely with the ~15 000 K temperature deduced from the Mariner 10 data as shown by Blum et al. (1980, 1981); (b) ~50% of the neutral H from (predominantly neutral) LISM is retained by charge exchange in the transition layer while the neutral He atoms go through, in view of the very small charge exchange cross section with the protons. However, in case (b) the population of neutral H atoms inside the heliosphere may significantly be affected by the H atoms that charge-exchanged in the shocked interstellar gas. This effect was as yet not evaluated. Other complications will result if the LISM magnetic field is strong enough to influence the structure (i.e. destroy the axial symmetry) of the discussed boundary layers or if it reconnects with the interplanetary magnetic field of solar origin (Akasofu and Covey, 1980; Ahluwalia, 1981). References (mainly period 1979-1981) Ahluwalia, H.S.: 1981, Adv. Space Res. 1, 151. Ajello, J.M., Witt, N. and Blum, P.W.: 1979, A & A 73,260. Akasofu, S.-L. and Covey, D.N., 1981: Planet. Space Sci. 29, 313. Artzner, G. et al.: 1981, A & A 100,205. Baranov, V.B.: 1981, Comm. on Astrophys. 9, 75. Baranov, V.B., Lebedev, M.G. and Ruderman, M.S.: 1979, Astrophys. Space Sci. 65,441. Baranov, V.B., Ermakov, M.K. and Lebedev, M.G.:·1981, pis'ma v Astr. Zh. 7, 372. Barker, E.S. et al.: 1980, Ap. J. 242, 383. Beard, D.B.: 1979, Ap. J. 234, 696. Bieszynski, S. and Grzedzielski, S.: 1982 (in preparation). Blum, P.W., Grzedzielski, S. and Witt, N.: 1980, Astrophys. Space Sci. 70,583. Blum, P.W., Grzedzielski, S. and Witt, N.: 1981, Adv. Space Res. 1, 197. Bourgin, M.S.: 1981, Comm. on Astrophys. 9, 157. Bridge, H.S. etal.: 1981, Science 212, 217. Broadfoot, A.L. et al.: 1981a, Science 212, 206. Broadfoot, A.L. et al.: 1981b, J. Geophys. Res. 86,8259. Brown, R.A. and Ip, W.-H.: 1981, Science 213, 1493. Bruhweiler, F.C. and Yoji Kondo: 1981, Ap. J. Let. 248, L 123. Cheng, A.F.: 1980, Ap. J. 242, 812. Clarke, J.T., Moos, H.W., Atreya, S.K. and Lane, A.L.: 1981, Nature 290, 19. Cook, J.W., Meier, R.R., Brueckner, G.E. and VanHoosier, M.E.: 1981, A & A 97,394. Curtis, S.A.: 1981, J. Geophys. Res. 86, 4715. Danby, J.M. and Camm, G.L.: 1957, MNRAS 117, 50. Dessler, A.J.: 1980, Icarus 44, 291. Dorman, L.I. and Ptuskin, V.S.: 1981, Astrophys. Space Sci. 79, 397. Eviatar, A. and Siscoe, G.L.: 1980, Geophys. Res. Let. 7, 1085. Fahr, H.J.: 1974, Space Sci. Rev. 15, 483. Fahr, H.J.: 1978, A & A 66, 103. Fahr, H.J., Ripken, H.W. and Lay, G.: 1981, A & A 102, 359. Fahr, H.J., Ripken, H.W. and Lay, G.: 1982, Plasma- dust interactions in the solar and cometary environment, Proc. IAU Symp. ERMA IV, Dubrovnik, 1981. Fisk, L.A., Kozlovsky, B. and Ramaty, R.: 1974, Ap. J. Let. 190, L105. Fisk, L.A.: 1976, J. Geophys. Res. 81, 4646. Fisk, L.A.: 1981, Adv. Space Res. 1, 41. Frisch, P.C.: 1981, Nature 293, 377. Gosling, J.T. et al.: 1980, J. Geophys. Res. 85, 3431. Grzedzielski, S.: 1980, planet. Space Sci. 28, 799. Grzedzielski, S. and Rozmus, W.: 1982 (in preparation). Haff, D.K., Watson, C.C. and Yuk L. Yung: 1981, J. Geophys. Res. 86, 6933. Hakamada, K. and Akasofu, S.-I.: 1981, J. Geophys. Res. 86, 1290. Holzer, T.E.: 1977, Rev. Geophys. Space Phys. 15, 467. Johnson, R.E., Lanzerotti, L.J., Brown, W.L., Armstrong, T.P.: 1981, Science 212, 1027. Jokipii, J.R. and Thomas, B.: 1981, Ap. J. 243, 1115.

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Judge, D.L., Wu, F.-U. and Carlson, L.W.: 1980, science 207, 431. Keller, H.U., Richter, K. and Thomas, G.E.: 1981, A & A 102,415. Keller, H.U. and Thomas, G.E.: 1979, A & A 80, 227. Kirsch, E.,Krimigis, S.U., Kohl, J.W., Keath, E.P.: 1981a, Geophys. Res. Let. 8,169. Kirsch, E., Krimigis, S.M., Ip, W.H., and Gloeckler, G.: 1981b, Nature 292,718. Kumar, S. and Broadfoot, A.L.: 1979, Ap. J. 228, 302. Kunc, J.A.: 1980, planet. Space Sci. 28, 815. Leinert, C., Hanner, M. and pitz, E.: 1978, A & A 63, 183. McDonald, F.B. et al.: 1981, Ap. J. Let. 246, L 165. McElroy, M.B. and Young, Y.L.: 1975, Ap. J. 196, 227. Meier, R.R.: 1977, A & A 55, 211. Meier, R.R.: 1979, A & A 79, 277. Mendis, D.A., Hill, J.R., Houpis, H.L.F., Whipple, E.C. Jr.: 1981, Ap. J. 249,787. Morfill, G.E. and Grtin, E.: 1979, Planet. Space Sci. 27, 1283. Mukai, T. and Schwehm, G.: 1981, A & A 95, 373. Mukai, T. and Yamamoto, T.: 1979, P.A.S. Japan 31, 585. Paresce, F., Fahr, H.J. and Lay, G.: 1981, J. Geophys. Res. 86, 1003. Petelski, E.F.: 1981, J. Geophys. Res. 86, 4803. Petelski, E.F., Fahr, H.J., and Ripken, H.W.: 1980a, A & A 87, 20. Petelski, E.F., Fahr, H.J., and Ripken, H.W.: 1980b, Solar and Interplanetary Dynamics, Dryer & Tandberg-Hanssen (Eds.) p. 159. Pollack, J.B. and Witteborn, F.C.: 1980, Icarus 44, 249. Ripken, H.W. and Fahr, H.J.: 1980, Astron. Mitteilungen 50,46. Sandel, B.R. et al.: 1979, Science 206, 962. Schwenn, R., Rosenbauer, H., Muehlhauser, K.-H.: 1980, Geophys. Res. Let. 7, 201. Shemansky, D.E.: 1980, Ap. J. 242, 1266. Shernansky, D.E., Sandel, B.R. and Broadfoot, A.L.: 1979, J. Geophys. Res. 84, 139. Sittler, E.C., Scudder, J.D. and Bridge, H.S.: 1981, Nature 292, 7Il. Smith, B., Shoemaker, E.M. and Kieffer, S.W.: 1979, Nature 280, 738. Smyth, W.H.: 1981, Ap. J. 246, 344. Stanley, J.E., Singer, S.F., and Alvarez, J.M.: 1979, Icarus 37,457. Stone, E.C. and Miner, E.D.: 1981, Science 212, 159. Thomas, G.E.: 1978, Ann. Rev. Earth planet. Sci. 6, 173. Trafton, L.: 1981, Revs. Geophys. Space Phys. 19, 43. Wallis, M.K. and Hassan, M.H.A.: 1978, planet. Space Sci. 26, I I l. Wallis, M.K. and Wallis, J.: 1979, A & A 78, 41. Warwick, J.W. et al.: 1979, Science 206, 991. Weller, C.S. and Meier, R.R.: 1979, Ap. J. 227, 816. Weller, C.S. and Meier, R.R.: 1981, Ap. J. 246, 386. Witt, N., Ajello, J.M. and Blum, P.W.: 1979, A & A 73,272. Witt, N., Ajello, J.M. and Blum, P.W.: 1981, A & A 95, 80. Wolfe, J.H. et al.: 1980, Science 207, 403. Wu, F.-H. and Judge, D.L.: 1979a, Ap. J. 231, 594. Wu, F.-H. and Judge, D.L.: 1979b, J. Geophys. Res. 84, 979. Wu, F.-H. and Judge, D.L.: 1980, Ap. J. 239, 389. Hu, F.-M., Suzuki, K., Carlson, R.W. and Judge, D.L.: 1981, Ap. J. 245, 1145. Xue-Pu Zhao and Hundhausen, A.J.: 1981, J. Geophys. Res. 86,5423. Zwickl, R.D., Krimigis, S.M., Armstrong, T.P., and Lanzerotti, L.J.: 1980, Geophys. Res. Lett. 7, 453.

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IV. A.

EXTRAPOLATION TO THE NEARBY INTERSTELLAR MATTER (F. Paresce)

Observational Access to the Local Interstellar Medium

Two basic and complementary perspectives can be adopted in order to determine the correct ISM parameters at or near the heliopause. The first is that of the ISM gas residing in the inner solar system that has already transited through the solar wind - ISM boundary region and the second is that of the gas residing at distances of 1-10 pcs from the sun that has yet to flow past the sun but will do so in the next 104-105 yrs. A comparison of the two sets of measurements should yield valuable information on the boundary conditions and, conversely, on their effect on the ISM conditions. It will, of course, also be assumed that the gas is uniform over distances of ~1 pc or less. B.

The "Inside" Aspect of the LISM

As a matter of fact, the relatively high speed of the neutral ISM gas with respect to the sun (~20 km/s- l ) allows its deep penetration into the solar system before it can be appreciably ionized. Most ISM particles can be found at ~90% of their undisturbed interstellar density values within a region of 1-5 AU of the sun. Within this region can also be found the highest densities of ions resulting from the ionization of the ISM neutrals. This proximity of the ISM to the sun can be conveniently exploited by observers in or near the earth. A careful analysis of the solar ultraviolet spectrum (see for example, White, 1977) shows that there are a number of intense emission lines that could, in principle, resonate with ISM particles or their derivatives. These include the prominent CII, 1336; 01, 1304; HI, 1216; NIl, 1085; HI, 1025; OIl, 834; He I, 584; He II, 304 A chromospheric emission features. Due to experimental limitations, only the HI, 1216 and the He I, 584 A lines amongst these can be used effectively for this purpose. Very recently the He II, 304 A line emission structure has been explored to a limited extent (Paresce et al., 1981; Lay et al., 1980). Recently first HI Ly-S measurements were reported (Shemansky et al., 1979). Recent observations of the resonantly scattered hydrogen Lyman-a and He 1,584 A interplanetary emissions have been extremely useful in confirming, extending and appreciably narrowing the earlier range of acceptable ISM parameters (Thomas and Krassa, 1971; Bertaux and Blamont, 1971; Paresce et al., 1973). A wide variety of techniques and observing platforms have been exploited, including low spatial and spectral resolution (Weller and Meier, 1976, 1979, 1981), low spatial and high spectral resolution (Freeman et al., 1976, 1980; Fahr et al., 1978; Lay et al., 1980), high spatial and low spectral resolution (Freeman et al., 1977, 1979), high spatial and spectral resolution (Adams and Frisch, 1977) detectors from earth orbit and a similar mixture of measurements from interplanetary probes (Broadfoot and Kumar, 1978; Ajello, 1978; Bertaux et al., 1976, 1977; Ajello et al., 1979). Since the ISM parameters are not measurable directly by any of these techniques because they are too intimately interrelated,they are obtained only as a result of comparisons with theoretical models with free adjustable parameters. A vigorous effort has been expended on the development of suitable and accurate models. These now take into account, in one way or another and with varying success, the effects of non zero gas temperatures, mUltiple scattering and electron and proton heating enhanced ionization by nonthermal and thermal electron impact (Meier, 1977; Thomas, 1978; Wallis and Wallis, 1979; Wu and Judge, 1978, 1979, 1980; Wallis and Hassan, 1978; Fahr, 1978; Keller et al., 1981; Petelski et al., 1980). Other special effects such as solar variability (Thomas, 1976), galactic emission (Thomas and Blamont, 1976), solar line shape uncertainties, solar wind and radiation anisotropies (Witt et al., 1979; Kumar and Broadfoot, 1978), neutralization of solar wind H+, He++, and He+ by zodiacal dust (Holzer, 1977; Fahr et al., 1981) penetration of interstellar dust (Bertaux and Blamont, 1976), enhanced solar wind - ISM interaction due to electron impact ionization of hydrogen (Petelski et al., 1980) have been

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considered but it is not yet clear what their contributions to the overall uncertainties of the experimental determinations are. In a recent workshop organized by the Max Planck Institut fur Aeronomie in Lindau, West Germany in 1980, a number of observers and theoreticians have attempted to reach a consensus on the appropriate values of the ISM gas parameters deduced by these techniques. Because of the considerable experimental and theoretical difficulties it is not too surprising that there exists a rather discomfitingly wide range of possible physical parameters. This state of affairs is also due, in part, to the undeniable fact that the scattered intensities are not always very sensitive to any one particular parameter. The rather diffuse character of the very few features observable in the backscattered radiation pattern at 1216 and 584 A represents a substantial obstacle to the goal of acquiring accurate values of the ISM parameters. The distant hydrogen density nR should be in the range of 0.04,::: n R .::: 0.08 cm- 3 the helium density between 0.008 ~ n Re ~ 0.015 cm- 3 , temperature between -1 6000 .::: T ~ 14 000 oK, the LSR velocity vector of modulus 15 ~ Ivl .: : 20 km/s oriented along the direction 250 ~ 1 ~ 315 0 , -25 ~ b ~ _20. Although the scatter of the measurements within the cited ranges seems fairly uniform, there is a slight tendency that cannot, at present, be ignored or conclusively ascribed to observational error, for the helium observations to yield higher gas temperatures than the hydrogen observations by a few thousand oK and a slightly different flow direction by ~15-200. The accuracy of measurement will have to be increased substantially to confirm this surprising effect. Nevertheless, it seems to be clearly established that the gas is in a lukewarm phase, slightly ionized and possessing an inherent motion originating roughly from the direction of the Scorpius-Centaurus region of the galaxy. A serious problem that is often overlooked concerns the validity of the assumption that the ISM conditions obtained by probing its structure out to, at most, a few tens of AU from the sun are at all appropriate for the gas at a few hundred or a few thousand AU at or near the solar bowshock and heliopause. As was mentioned before, because of our ignorance of the precise physical characteristics therein, it is difficult to assess the magnitude of this effect. Conventional wisdom has it that helium will flow through undisturbed due to the smallish or negligible cross sections for the relevant interactions while hydrogen will have a harder time, especially if the bulk velocity is low (Fahr, 1974; Wallis, 1978; Ripken and Fahr, 1982). Thus, it should always be kept in mind that there is a far from negligible probability that the quoted value of n R at least is lower, perhaps substantially lower, than the appropriate value at large distances from the interaction region. One might even be tempted to attribute the putative temperature and flow direction differences in the hydrogen and helium gases seen in the inner solar system to unspecified mechanisms operating near the solar wind - ISM boundary. Two concepts that should be pursued vigorously in the near future are 1) direct in situ sampling of the interplanetary wind particles by means of a direct particle detector on an interplanetary probe and 2) high spectral resolution observations of the two most prominent lines. An instrument to carry out the former investigation was built for the forthcoming ESA solar-polar mission so that ISM neutrals will be measured out to ~ 5 AU and also at high ecliptic latitudes (Rosenbauer and Fahr, 1977). This technique should represent a considerable leap forward in measurement accuracy and has the fundamental advantage of being able to unravel the tight interdependencies between density, temperature, and velocity. High spectral resolution is another high priority in this field both as a means of separating terrestrial from interplanetary emission (Adams and Frisch, 1977) and, even more important, to actually resolve the line. Preliminary low sensitivity measurements of this sort have been recently attempted on the Re I, 584 A line using resonance gas cell methods and have yielded promising results (Freeman et aI., 1976, 1980; Fahr et aI., 1978; Lay et aI., 1980). Spectral resolution and separation problems can best be overcome by the use of large earth-orbiting telescopes with high resolution spectrographs such as IUE or, better, the upcoming Space Telescope that could be used to observe the Lyman-a line to determine its Doppler shift with respect to the geocoronal line for various view directions and times of year.

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Imprecise as these measurements may be, they are extremely useful for our understanding of the structure of interstellar matter. The fundamental aspect here is that they probably represent the most direct evidence for the existence of the lukewarm phase first postulated by Field et al., (1969) and whose presence was only otherwise inferred from HI 21 cm absorption and emission observations (Radhakrishnan, 1974; Baker, 1979 and references therein). Since this gas is very inconspicuous in optical and ultraviolet absorption line studies, some have even argued that it does not exist at all (Scott et aI., 1977). It is now clear, however, that the very undeniable presence of a hot tenuous gas at T~105 -10 6K implied both by OVI absorption and soft X-ray and EUV diffuse background observations (Jenkins, 1978a,b; Tanaka and Bleeker, 1977; Cowie et al., 1979; Fried et al., 1980; Davelaar et al., 1980; Paresce and Stern, 1981) and the presence of cooler clouds absolutely requires a gas at an intermediate temperature. In this picture, the hot low density phase is maintained in these conditions by the repeated passage of supernova or stellar wind shock "aves (McCray and Snow, 1979 and references therein) that also compress, accelerate and partially or totally evaporate the cool (T~10-1000K) gas clouds. Consequently, at the outer edge of these clouds, transition regions of intermediate temperature, density, and ionization structure represent the conductive interfaces between these two extreme phases (McKee and Ostriker, 1977). The ionization level of the resultant lukewarm (~104K) plasma is maintained in a precarious equilibrium by a complex and probably very spatially variable combination of cosmic ray, stellar and diffuse EUV radiation in the 50 - 1000 A range, the latter originating in the hot surrounding gas. Precise boundaries between the various phases are, of course, only useful schematizations of this complex and dynamic phenomenon. C.

Ionization Conditions in the ISM

The backscatter measurements of the ISM in the solar system can playa vital role in confirming or sharpening our understanding of this gas phase especially since it allows, in principle, a separation of the parameters that are often seriously interlocked in the interpretation of interstellar absorption lines. In fact, once the 50-3000 A radiation field near the sun is determined precisely, these observations should yield a complete and unique solution to the ionization structure and the heating mechanisms of the ISM. Specifically, assuming a normal cosmic H/He abundance ratio of 10 is valid, the degree of ionization of hydrogen implied by the backscatter measurements can be as high as ~50% with an associated electron density ne~0.05 cm- 3 . To maintain this state of affairs in a gas at 104K in photoionization equilibrium requires an ionization rate G ~ C(n~/nH ~ 2.1O- 14 s- 1 where C( is the recombination coefficient at that temperature. Similar values were obtained by Meier (1980). Since, under these assumptions, G ~ fooa(V)FvdV where a(v) is the photoionization cross section of hydrogen, G depen~s crucially on the radiation field intensity below 910 A impinging on the atom. Assuming Fv to be constant in the region just below the ionization edge, the required photon flux near the edge corresponding to the computed G is of the order of 10-20 photons cm- 2 s- 1A-1. Ionization by EUV photons below ~400 A will tend to decrease this number somewhat. Several attempts have been made recently to measure the intensity of the diffuse EUV radiation field in the solar vicinity (Paresce and Bowyer, 1976; Sandel et al., 1979) or to estimate it semi-empirically (Grewing, 1975; Blum and Fahr, 1976). In practice all that is available presently are measurements of specific intensity in a few directions as opposed to a total flux Fv that is necessary to compute G. Between 912 and ~200 A, only upper limits several orders of magnitude above the required flux have been determined which, then, cannot be used to constrain the ISM model described. The semi-empirical models constructed to account for the observed ionization structure of ISM clouds are consistent with the data reported here as long as the radiation temperature is less than 10 OOOoK (Blum and Fahr, 1976) to avoid the very high values of electron density determined by Grewing (1975). It is clear that little progress can be made in this field until precise measurements of the radiation field in the EUV are carried out, hopefully, in the next few years with the launch of an EUV Explorer.

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663

Large-Scale Diagnostics of the ISM

Independently of the question of how the warm ISM is maintained, it is interesting to determine its extent and structure in all directions around the sun. Interstellar hydrogen absorption of stellar spectra at 1216 A or of white dwarf emission in the EUV (Cash et al., 1979 and references therein) provides some information on this important question. Although the number of stars that can be observed in this way is dishearteningly small and the spatial coverage quite limited, it is rather clear that the very local hydrogen density of ~0.05 cm- 3 is roughly maintained out to a distance of ~4 pcs. A possibly higher density of ~O.I cm- 3 may be more appropriate in the range 1.3 - 3.5 pcs, so that the sun may be immersed in a slightly lower density region than the immediate surroundings. This result should be viewed wi'th some skepticism, however, since the quoted difference may well be within experimental errors and/or due to the assumption of negligible interaction with the heliopause. Beyond ~ Ilpcs, the density definitely drops to values oscillating between 0.01 and O. I cm- J with most stars below 0.05 cm- J • Beyond approximately 75 pc the density increases past O. I cm- 3 . For distances out to ~500 pc, the measured hydrogen column densities towards hot stars (Bohlin et al., 1978) show substantial variations from place to place in the sky, confirming the expected patchiness of the local ISM. Thus, the presence of a tenuous cloud of gas just in front or surrounding the sun of total column density 2- 5·]018 cm 2 and diameter of ~5 pc can be clearly inferred from these results. Since the column density remains roughly constant with distance beyond ]0 pc out to ~ 75 pc in many d.irections (HZ43 is the most notable example of this remarkable behaviour), the neutral hydrogen density must plummet to very low values beyond the edge of the cloud in which the sun is imbedded. This is logically interpreted as the rough boundary between the warm and the hot phase of the ISM and is consistent in general with the latest results of the EUV diffuse background observations (Paresce and Stern, 1981) that require a fixed slab of ~2. 10 18 cm- 2 of absorption in front of the hot plasma emission region that extends out to '" 100 pcs. If McKee and Ostriker's (1977) model is to be taken literally, the weakly ionized lukewarm phase in which the sun is apparently immersed should be located on the periphery of a cool, dense cloud a pc or so away that is slowly evaporating into the hot ISM beyond. Vidal-Madjar et al., 1978 have suggested that such a cloud may be at a distance of;:: 0.03 pc (2.]04 AU) from the sun in the direction of the Sco-Cen association. This claim is based on the possible existence of a strong HI density gradient in the local ISM, of a far UV flux anisotropy and on differences in the D/H ratio in different lines of sight. These premises have been disputed, however (McClintock et al., 1978). Since most diffuse clouds in the ISM are found to be marshalled in sheets rather than spheres (McCray and Snow, 1979) and the McKee and Ostriker model does allow for the existence of small clouds (R"'0.5 pc) without a core, its failure to be detected should not be unduly disturbing. A final noteworthy although highly speculative point that has been discussed at some length recently concerns the effects on solar and planetary structure and evolution of an encounter or repeated encounters with a dense (nH ~ ]02 cm- 3 ) interstellar cloud (Talbot and Newman, 1977; McKay and Thomas, 1978; Butler et al., 1978; Fahr, 1980; Ripken and Fahr, 1982 and references therein). It is, in fact, very unlikely for the sun to have avoided dense clouds in its ~5. 10 9 yr. lifetime. Approximately 10 2 such'encounters are expected, of which "'10 could have involved clouds with nH in excess of 10 3 cm- 3 . The practical consequences on the earth including the triggering of ice ages are of great significance and have been discussed in detail by McKay and Thomas (1978). As the hydrogen density at the heliopause increases, its position is shifted closer and closer to the sun. The crucial parameter here is the value of ~ for which the supersonic wind is confined by the ISM to a region whose radius is smaller than 1 AU in the case of the earth. Using the similar mass, momentum and energy continuity equations with interaction terms describing the present low density ISM-solar wind scenario, Ripken and Fahr (1982) have shown that this critical point is reached at n H '" 1.2.10 2 cm- 3 . This surprisingly low value implies that the earth has probably resided many and long times in the

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undisturbed ISM and without its normal solar wind shield. Effects on the sun, however, should be minimal for even the densest ISM clouds cannot completely choke off the solar wind. References Adams, T.F. and Frisch, P.C.: 1977, Ap. J. 212, 300. Ajello, J.M.: 1978, Ap. J. 222, 1068. Ajello, J.M., Witt, N. and Blum, P.W.: 1979, A & A 73, 260. Baker, P.L.: Global physical characteristics of the HI gas, in "The large scale characteristics of the galaxy", ed. W.B. Burton, IAU Symp. No. 84, D. Reidel, Dordrecht, p. 287, 1979. Bertaux, J.L. and Blamont, J.E.: 1971, A & All, 200. Bertaux, J.L. and Blamont, J.E.: 1976, Nature 262, 263. Bertaux, J.L. et al.: 1977, Nature 270, 156. Bertaux, J.L. et al.: 1976, A & A 46, 19. Blum, P.W. and Fahr, H.J.: 1976, Astrophys. Space Sci. 39, 321. Bohlin, R.C., Savage, B.D. and Drake, J.F.: 1978, Ap. J. 224, 132. Broadfoot, A.L. and Kumar, S.: 1978, Ap. J. 222, 1054. Butler, D.M., Newman, M.J. and Talbot, R.J.: 1978, Science 201, 522. Cash, W., Bowyer, S. and Lampton, M.: 1979, A & A 80, 67. Cowie, L., Jenkins, E.B., Songaila, A., and York, D.G.: 1979, Ap. J. 232, 467. Davelaar, J., Bleeker, J.A.M. and Deerenberg, A.J.M.: 1980, A & A 92, 231. Fahr, H.J.: 1974, Space Sci. Rev. 15, 483. Fahr, H.J.: 1978, A & A 66, 103. Fahr, H.J.: 1980, Mittg. Astron. Ges. 47, 233. Fahr, H.J., Lay, G. and Wulf-Mathies, C.: 1978, Space Res. 18, 393. Fahr, H.J., Ripken, H.W. and Lay, G.: 1981, A & A 102, 359. Field, G.B., Goldsmith, D.W. and Habing, H.J.: 1969, Ap. J. Let. 155, L149. Freeman, J., Paresce, F. and Bowyer, S.: 1979, Ap. J. Let. 231, L37. Freeman, J., Paresce, F., Bowyer, S. and Lampton, M.: 1976, Ap. J. 208, 747. Freeman, J. et al.: 1977, Ap. J. Let. 215, L83. Freeman, J., Paresce, F., Bowyer, S. and Lampton, M.: 1980, Astron. Astrophys. 83,58. Fried, P.M., Nousek, J.A., Sanders, W.T. and Kraushaar, W.L.: 1980, Ap. J. 242, 987. Grewing, M.: 1975, A & A 38, 391. Holzer, T.E.: 1977, Rev. Geophys. Space Phys. 15, 467. Jenkins, E.B.: 1978a, Ap. J. 219, 845. Jenkins, E.B.: 1978b, Ap. J. 220, 107. Keller, H.U., Richter, K. and Thomas, G.E.: 1981, A & A 102, 415. Kumar, S. and Broadfoot, A.L.: 1978, A & A 69, L5. Lay, G., Fahr, H.J. and Wulf-Mathies, C.: Spectrometric investigations of He-l/ll resonance emissions with a rocket-borne multisensor resonance cell instrumentation, Proc. 5th ESA-PAC Symp. on European Rocket and Balloon Progr. and Related Research, Bournemouth, 1980. (ESA SP-152, 445, 1980). McClintock, W., Henry, R.C., Linsky, J.L. and Moos, H.W.: 1978, Ap. J. 225, 465. McCray, R. and Snow, T.P.: 1979, Ann. Rev. Astr. Ap. 17, 213. McKay, C.P. and Thomas, G.E.: 1978, Geophys. Res. Let. 5, 215. McKee, C.F. and Ostriker, J.P.: 1977, Ap. J. 218, 148. Meier, R.R.: 1977, A & ASS, 211. Meier, R.R.: 1980, A & A 91,62. Paresce, F. and Bowyer, S.: 1976, Ap. J. 207, 432. Paresce, F. and Stern, R.: 1981, Ap. J. 247, 89. Paresce, F., Bowyer, C.S. and Kumar, S.: 1973, Ap. J. Let. 183, L87. Paresce, F., Fahr, H.J. and Lay, G.: 1981, J. Geophys. Res. 86, 10038. Petelski, E.F., Fahr, H.J., Ripken, H.W., Brenning, N., Axnas, 1.: 1980, A & A 87,20. Radhakrishnan, V.: The observational evidence for an intercloud medium, in Galactic Radio Astronomy, ed. F.J. Kerr and S.C. Simonson, IAU Symp. No. 60, D. Reidel, Dordrecht, p. 3, 1974.

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Ripken, H.W. and Fahr, H.J.: Solar wind interactions with neutral hydrogen inside the orbit of the earth, in Lecture Notes in Physics, Springer-Verlag, Heidelberg, 1982. Ripken, H.W. and Fahr, H.J.: Modification of interstellar gas parameters in the heliospheric interface, preprint, 1982. Rosenbauer, H. and Fahr, H.J.: Direct measurement of the fluid parameters of the nearby interstellar gas, using helium as tracer, Technical Proposal NASA/ESA 1977 . Sandel, B.R., Shemansky, D.E. and Broadfoot, A.L.: 1979, Ap. J. 227, 808. Scott, J.S., Jensen, E.B. and Roberts, W.W.: 1977, Nature 265, 123. Shernansky, D.E., Sandel, B.R. and Broadfoot, A.L.: 1979, J. Geophys. Res. 84, 139. Talbot, R.J. and Newman, M.J.: 1977, Ap. J. Suppl. Ser. 34, 295. Tanaka, Y. and Bleeker, J.A.M.: 1977, Space Sci. Rev. 20, 815. Thomas, G.E.: Interaction of interstellar neutral hydrogen and the solar system, AGU Int. Symp. Solar-Terr. Phys., Boulder, Colo., 1976. Thomas, G.E.: 1978, Ann. Rev. Earth planet. Sci. 6, 173. Thomas, G.E. and Blamont, J.L.: 1976, A & A 51,283. Thomas, G.E. and Krassa, R.F.: 1971, A &A 11, 218. Wallis, M.K.: 1978, Space Res. 18, 401. Wallis, M.K. and Hassan, M.H.A.: 1978, planet. Space Sci. 26, Ill. Wallis, M.K. and Wallis, J.: 1979, A & A 78, 41. Weller, C.S. and Meier, R.R.: 1976, Ap. J. 203, 769. Weller, C.S. and Meier, R.R.: 1979, Ap. J. 227, 816. Weller, C.S. and Meier, R.R.: 1981, Ap. J. 246,386. White, O.R., ed.: The solar output and its variations, Colorado Associated Universities Press, Boulder, 1977. Witt, N., Ajello, J.M. and Blum, P.W.: 1979, A & A 73, 272. Wu, F.M. and Judge, D.L.: 1978, Ap. J. 225, 1045. Wu, F.M. and Judge, D.L.: 1979, Ap. J. 231, 594. Wu, F.M. and Judge, D.L.: 1980, Ap. J. 239, 389. Wulf-Mathies, C. and Blum, P.: 1976, Space Res. 16, 665.

50.

IDENTIFICATION AND PROTECTION OF EXISTING AND POTENTIAL OBSERVATORY SITES (PROTECTION DES SITES D'OBSERVATOIRES EXISTANTS ET POTENTIELS) (Committee of the Executive Committee)

PRESIDENT: F.G. Smith VICE-BRESIDENT: A.A. Hoag ORGANIZING COMMITTEE: C.A. Anguita, W. Mattig, C. Blanco, F. Bertola, M.F. Walker, J.T. Jeffries, R. Cayrel. 1.

Joint IAU/CLE Report

The most noteworthy action by this Commission is the issue in 1980 of "Guidelines for minimizing Urban Sky Glow near Astronomical Observatories" (Cayrel and Smith, 1980). This is a joint publication of IAU and CIE (Commission Internationale de l'Eclairage). It represents a practical approach to the most serious problem facing all observatories: the increase of light pollution from urban areas. Taking the previous recommendations of Commission 50 into account, the report shows how natural and artificial sky glow affects astronomical observations, describes methods of avoiding excessive artificial sky glow, and shows how public regulations have been successfully applied to protect individual observatories. 2.

Identification of Observatory Sites

Some of the qualities required of an observatory site are easy to assess: freedom from cloud, freedom from sky glow, ease of access. Others may require extensive measurement: seeing, sky transparency, water vapour content. Although simple methods may be available for their measurement, little is known about the relative merits of good sites in these latter respects. The Commission is therefore studying techniques of measurement and assessing the results of all available measurements. In particular, the growing importance of infra-red observations has emphasised the need for water vapour measurements at high altitude sites. Sites for solar observations have been surveyed by the Joint Organisation for Solar Observations (Brandt and Wtlhl, 1971); favourable daytime conditions have been found at Roque de los Muchachos Observatory on La Palma. There is justifiable anxiety about the availability of sufficient first-class sites with a reasonable geographic distribution. A wide distribution is obviously desirable so that all observers can have reasonably easy access to first-class instruments: there is, however, a vital observational need for a spread in longitude for the study of variability in astronomical objects. The location of suitable sites will require many observations and a deeper Understanding of the atmosphere. 3.

Monitoring existing sites

Working observatories are busy places, and regular objective measurements of sky conditions are seldom made and recorded. The Commission emphasises the value of such measurements, not only to the work of each observatory but to atmospheric physics. Seeing conditions are sometimes determined by local circumstances, such as poor dome design or local topography (Hartley et al. 1981), but there is always a component of seeing originating in the atmosphere which at some sites and on some occasions reduces to the order of ! arc sec. A radio-sonde investigation 667

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COMMISSION 50

by Barletti et al. (1977) suggests that sub-arc second seeing might often be available at goo~ sites. ~f such conditions can be sufficiently relied upon, the next generatlon of optlcal telescopes should be designed to take advantage of them. Sky transparency has a particular interest. Dr. P.J. Edwards (Physics Department, University of Otago 1 Dunedin, New Zealand) suggests that extensive measurements of atmospheric extlTIction at existing high altitude observatories might be of benefit in atmospheric studies. He already has a network of five observatories in New Zealand to produce data on a routine basis, and he would welcome collaborators from other countries. Night sky brightness is known to vary through geographical factors and solar activity. A systematic observational study would be of great interest in the choice of astronomical sites. The Commission would be glad to receive proposals for such a study. 4.

Recent site-testing campaigns

The National Centre for Science and Technology in Saudi Arabia has commissioned the National Research Council Canada to test sites for optical telescopes. The testing is organised by Dr. Elmar Brosterhus, who recently published test results for Mt Kobau in British Columbia (Brosterhus et al. 1972). A summary of the results of the British tests on La Palma, Hawaii and Maderia has been published by McInnes (1981). Yunnan Observatory, of Academia Sinica, tested three sites in Binchuan in 1979 and 1980 (Huang Yin-Liang et al. 1981). A search using satellite infra'-red photographs has led to the choice of an observatory site at Laguna de Otun, 3,950 m altitude, in Columbia (reported by Dr. Jonge Arias de Greiff, Director, Observatorio Astronomico Nacional, Bogota). A new site survey at Mauna Kea and other sites in USA, organised by Dr. Crawford of Kitt Peak National Observatory, includes measurements of ahsorption by water vapour. The results will be valuable both for infra-red and millimetre wave astronomy. 5.

Satellite Power System

A proposal to place a network of very large solar power collectors in orbit round the earth (the SPS system) has disastrous implications both for optical and for radio astronomy. If the system at present under study were eventually to be put into operation, reflected sunlight from the satellites, each of which might have 55 km2 of solar cells, would remove all possibility of dark sky observations over a large proportion of the sky (Boyce, 1980). The Commission brings this to the attention of the General Assembly of the IAU. References Barletti, R., Ceppatelli, G., Paterno, L., Righini, A. and Speroni, N.: 1977, Astron. &Astrophys. 54, 649. Boyce, P.B.: 1980, Bull.Amer.Astron.Soc., 12,501. Brandt, P.N. and Wtlhl, H.: 1971, Joint Organisation for Solar Observations Annual Report 1970. Brosterhus, E., Pfannenschmidt, E. and Younger, F.: 1972, Jr.R.astr.Soc. Canada, 66, No.I. Cayrel, R. and Smith, F.G.: 1980, "Guide Lines for minimising Urban Sky Glow near Astronomical Observat0ries", Publication IAU/CIE No.I. Hartley, M., McInnes, B. and Smith, F.G.: 1981, Q.Jr.R.astr.Soc. 22, 272. Huang Yin-Liang et al: 1981, Acta Astrophysica Sinica, 1, 158. McInnes, B.: 1981, Q.Jr.R.astr.Soc. 22, 266.

WORKING GROUP FOR PLANETARY SYSTEM NOMENCLATURE (NOMENCLATURE DU SYSTEME PLANETAlRE) (Committee of the Executive Committee) PRESIDENT: P.M. Millman. VICE-PRESIDENT: H. Masursky. MEMBERS: B.Yu. Levin, D. Morrison, T.C. Owen, G.H. Pettengill, V.V. Shevchenko, B.A. Smith, V.G. Tejfel', E.A. Whitaker. CONSULTANTS: J.M. Boyce, W.E. Brunk, K.P. Florenskij, A.M. Kollikov. The Working Group is assisted by five nomenclature Task Groups. These prepare the detailed lists of names for discussion by the WGPSN. The membership of the Task Groups is listed below:MOON V.V. Shevchenko (Chairman), A. Dollfus, F. EI-Baz, K.P. Florenskij, H. Masursky, P.M. Millman, S.K. Runcorn, E.A. Whitaker. MERCURY D. Morrison (Chairman), M.E. Davies, A. Dollfus, K.P. Florenskij, O.J. Gingerich, J.E. Guest. VENUS G.H. Pettengill (Chairman), D.B. Campbell, R.M. Goldstein, M.Ya. Marov, H. Masursky. MARS B.A. Smith (Chairman), A. Dollfus, M.Ya. Marov, D.Ya. Martynov, H. Masursky, S. Miyamoto, C. Sagan. OUTER SOLAR SYSTEM T.C. Owen (Chairman), K. Aksnes, M.S. Bobrov, A. Brahic, M.E. Davies, N.P. Erpylev, H. Masursky, B.A. Smith, V.G. Tejfel'. The seventh meeting of the WGPSN was held in Budapest, Hungary, 6 June, 1980, and the eighth meeting in Bath, England, 16 April, 1981. The ninth meeting is scheduled for 16 August, 1982 in Patras, Greece. It has been noted that the WGPSN has lacked a direct contact with the People's Republic of China and steps are being taken to correct this. Guidelines for naming newly-discovered satellites of the planets in the outer solar system have been formulated. The following names have been assigned:Jupiter XIV 1979 Jl Adrastea Jupiter XV 1979 J2 Thebe Jupiter XVI 1979 J3 Metis. General guidelines have also been established for naming topographical features on the solid surfaces of the satellites in the outer solar system. In addition to words associated with the myths surrounding each satellite name the following categories have been used for names on seven of the satellites of Saturn - MlMAS, Morte Darthur; ENCELADUS, Arabian Nights; TETHYS, Odyssey; DIONE, Aeneid; RHEA, Creation Myths; HYPERION, Sun and Moon Dieties; IAPETUS, Song of Roland. Initial notation for newly discovered planetary rings has been outlined in conformity with the notation used for other discoveries in the solar system. Examples of the recommended preliminary notations are:1982 U8R for the eighth ring discovered in 1982 around Uranus; 1984 NIR for the first ring discovered in 1984 around Neptune. A "GAZETTEER of Planets and Satellites (as approved by the International Astronomical Union)" is nearing completion and will contain approximately 3400 names used on 18 planetary bodies. This is a joint effort of the Working Group, assisted by the Task Groups. The detailed lists of names added since the last General Assembly in Montreal, 1979, will be published in Transactions of the I.A.U. Vol. XVIIIB. P •M. MILLMAN

President of IAU/WGPSN 669