This report covers the period July 1, 1987, to about June 30, 1990. The task of preparing the individual sections has been carried mainly by members of the Organizing Committee and chairmen of the Working Groups. All authors have to be thanked for this service to the community. The authors were free to emphasize what seemed important to them, rather than to attempt completeness. It is hoped that the abbreviated references are self-explanatory; in some cases the code numbers of Astronomy and Astrophysics Abstracts are used. A + sign stands for et alii.

In the triennium under review, from the late second half of 1987 to the early second half of 1990, Commission 29 has sponsored or cosponsored the following IAU Conferences: Coll. No. 106, “Evolution of Peculiar Red Giant Stars,” Bloomington, Indiana, July 1988; CoU. No. 114, “White Dwarfs,” Hanover, New Hamsphire, August 1988; Coll. No. 113, “Physics of Luminous Blue Variables,” Val Morin, Quebec, August 1988; Coll. No. 122, “Physics of Classical Novae,” Madrid, Spain, June 1989; Symp. No. 143, “Wolf-Rayet Stars and Interrelations with Other Massive Stars in Galaxies,” Denpasar, Indonesia, June 1990; Symp. No 148, “The Magellanic Clouds and their Dynamical Interaction with the Milky Way,” Sydney, Australia, July 1990; Symp. No. 145, “Evolution of Stars: the Photospheric Abundance Connection,” Druzba, Bulgaria. August 1990.

The work of IAU Commission 31 is contained in the following sections contributed by the Members.

The two Working Groups installed during the period 1984-1987 :

This report is intended to provide references to works done during the triennium 1988-1990 (including references for 1987) in the general field of galactic structure.

“Astronomy and Astrophysics Abstracts” provides an exhaustive list of works related to galactic structure and dynamics and it is not the aim of this report to duplicate this already existing service. Only a selection of works, illustrating some trends and highlights (a subjective view !), are described here and will certainly allow a comprehensive view of the broad domain of galactic research.

This report covers the period summer 1987 – summer 1990. It is divided into sections written by various experts in each subfield. I would like to thank the many individuals who worked hard in preparing this report. Without their cooperation and hard work this report would not exist.

The following summaries usually begin with a list of general references in the particular subfield (monographs, catalogs, and relevant symposia). Subsequent references to these volumes are sometimes identified by only the editor’s name, underlined, plus a page number. All references are given with only one name, followed by a + sign if there are additional authors. The citations in the Soviet and Chinese literature are given in the corresponding journals of English translations, which of course provide the references to the original journal. I have edited several contributions to force them to fit into just slighdy more than the space we were allowed, but all papers originally cited are in this version.

In previous reports, short reviews of the recent developments in a few selected major topics have revealed themselves very valuable and we go on with this useful practise. The subjects are: Stars of very low luminosity: red, brown and white dwarfs (F. D’Antona), Solar models (P. Demarque) and a short note on The observation of the solar neutrinos by the Kamiokande collaboration (Y. Totsuka), The HR diagrams for massive stars in the Magellanic Clouds (Ed. L. Fitzpatrick), Late evolution of asymptotic giant branch stars: clues from IR and radio observations (S. Kwok), SN 1987A (J.C. Wheeler), Binary and millisecond radio pulsars and evolution of close binaries (E. van den Heuvel), Progresses in computational methods for stellar models (G. Meynet). I am very grateful to the authors for providing promptly these very useful reviews.

This report is the assembled and edited contributions of several members of the organizing committee, and as such ranges widely in style and content. It is not our intent to give here a complete review or full coverage of research falling within the domain of our commission. Instead, it is a sample of some of the more important issues studied during the last three years.

The following commission members have contributed to this report:

W.J. Altenhoff, H. Andernach, J. Baars, R. Chini, R.J. Cohen, J.J. Condon, Y. Fukui, R. Güsten, J.M. van der Hulst, C. Henkel, W. Huchtmeier, M. Ishiguro, T. Krichbaum, M, Kundu, A. Lazenby, W. Reich, P. Roelfsema, S.E. Thorsett, R. Tuffs, CM. Walmsley, H. Wendker, R. Wielebinski, T.L. Wilson (organizer), A. Witzel

Aperture Synthesis Telescopes - Commissioning tests and observations have been made using three antennas in the Australia Telescope (AT), spaced up to 2km apart, and the first image of a radio source observed at 6cm was produced in 1989. The IRAM millimeter array in France comprizing three 15-m antennas has been commissioned at 3mm. A fourth antenna is planned as well as operation at 1mm. The three element Berkeley-Illinois-Maryland Array (BIMA) at Hat Creek is being expanded to six 6-m antennas and a new correlator with 1024 channel up to 830MHz bandwidth. Plans to expand to 9 antennas are final. The Owens Valley three-element millimeter array has been operated at 1mm, the shortest wavelength for the radio interferometry; a digital correlator with 500MHz bandwidth is under construction and the array will be extended to 6 antennas. In Japan at NRO the Nobeyama Millimeter Array equipped with SIS receivers and 320MHz bandwidth "FX" correlator is now operational at 3mm and 7mm wavelengths. New SIS receivers for 1mm and 2mm are under construction and a sixth 10-m antenna is planned. The Cambridge 5-km telescope, now the Ryle Telescope, has been substantially upgraded. The overall sensitivity of the instrument is being increased by a factor of ~20. The Giant Metrewave Radio Telescope, being built at Khodad near Pune in India, has made considerable progress and is expected to be operational by 1992-93.

During the XXth General Assembly the Commission agreed to support a motion by Commissions 19 and 31 that a history be prepared of the Bureau Internationale de l’Heure and the International Polar Motion Service; the rider wad added that the two authors proposed (B. Guinot and S. Yumi) obtain the services of a professional historian of astronomy, to advise and assist where possible.

By the end of the XXth General Assembly in Baltimore, the number of Commission 42 members had increased to 305. Subsequently, D. Ya. Martynov has died and 11 new members have been added.

The last Draft Report showed a healthy rate of growth in citations of Sections 117 (Close Binaries), 119 (Eclipsing Binaries), and 120 (Spectroscopic Binaries) of Astronomy and Astrophysics Abstracts from 1982 through 1986. The number of these citations has continued the mean trend with 976 and 1015 references for 1987 and 1988, respectively. As the Past-President remarked, these counts are considerable underestimates of the total literature concerning close binaries (hereafter, CB’s). A personal appreciation of the total corpus of work is that quality remains very high and content has become much richer as more and more associations have been made with generalized stellar studies. In part, this may be traced to the everincreasing awareness by the general community of the experiments in stellar evolution which Nature runs in CB’s.

The 1987-90 triennium has been a prosperous one for space astronomy. The field has benefited from diverse activities, ranging in style from the continued operation of some old instruments, such as uv spectrographs aboard IUE and Voyager, to the introduction of completely new observing techniques, such as the Hipparcos mission to perform astrometry over large angles and the radio Very Long Baseline Interferometry (VLBI) demonstration with the NASA’s Tracking and Data Relay Satellite System (TDRSS). We have witnessed some important highlights in space astronomy which significantly enhanced our understanding of some fundamental problems in astrophysics. For instance, the COBE satellite offered a tremendous gain in the precision of measuring the cosmic background radiation, and initial results seem to authenticate the simple character of this microwave radiation. As noted in the previous report of Commission 44, Supernova 1987A in the Large Magellanic Cloud was the brightest supernova since the one sighted by Kepler in 1604. There have been remarkable improvements in astronomical instruments since Kepler’s time, and the fruits of our good fortunes with 1987A are now appearing in the literature. Finally, the long anticipated launch of our biggest enterprise in space astronomy, the Hubble Space Telescope, occurred in the spring of 1990.

As an introduction to this report I would like to cite two comments from the book MK Process and Stellar Classification (ed. by R.F. Garrison, 1984). The first is from the article by W.W. Morgan The MK system and the MK process: “The MK system furnishes a satisfactory frame of reference for stars of Population I in the solar neighborhood; but when we consider the variety of stellar spectra encountered in our galaxy and in other stellar systems we are unable to classify many stars satisfactorily from the MK standards alone. What we now require is a more general frame of reference – or frames of reference – that will accept with precision a greater variety of ‘specimens’ (stellar spectra).” The second is an excerpt from one of the conclusions in the article by D.L. Crawford The relationship between the MK system and photometric classification: “The future potential of all this classification work is great. Technological change is rampant, and most interesting. New and powerful 1(λ) machines will be with us soon, as well as direct CCD photometers. Their power is great and we’ll all end up using them. The opening of new wavelength regions is a fantastic advantage to classifiers. The challenges and opportunities are vast.”

During the last three years there have been technical improvements in CCD detectors and as a result they are now much better adapted to the needs of photometry and spectroscopy. Signal processing by modern computers now permits rapid utilization of large quantities of information. Technical progress in detectors and computer science now provides us with powerful and relatively low-cost tools for computation, and leads us to view with optimism the development of the powerful 1(A) machines anticipated by Crawford.

Commission 46 is a commission somewhat out of the ordinary and can in some ways be considered as an extended arm of the Executive Committee of the IAU. National Committees or Adhering Bodies in each member country nominate one person per country to be the national representative to the Commission. The National Representative maintains liaison between the Commission and the home country, writes a national triennial report on the development of astronomy education and votes on financial matters. Other IAU astronomers, with a special interest in education, can become regular individual members of the Commission. Non-IAU members can be invited by the Commission to serve for one triennial term, this is renewable.

The last three years have been very fruitful ones in cosmology research. Brilliant achievement on the spectrum and homogeneities of cosmic microwave background radiation by COBE satellite is an example. It is, however, obviously impossible to review achievements in all fields in the number of pages allocated to our commission. This report, as in past reports, consists of some details of only some selected topics. I invited six active colleagues to collaborate in the preparation of this report. The topics are 1) Large Scale Structure and Motion (A. Dekel), 2) Formation of Galaxies and Large Scale Structure (S. Shandarin), 3) Active Galactic Nuclei in Cosmology (P.A. Shaver), 4) Cosmic Microwave Background Radiation (R. B. Partridge), 5) Primordial Nucleosynthesis (H. Reeves) and 6)The Cosmological Parameters (V. Trimble). Unfortunately, review on Early Universe could not be included because of the limit of page number, though it was planned originally. Recent developments in this area would be seen in the proceedings of recent international conferences (for example, Nobel Symposium 79 on ”The Birth and Early Evolution of Our Universe” Graeftavallen, Sweden, June, 1990, ed. B.-S. Skagerstam, World Scientific)

The heliosphere is a unique laboratory for in situ studies of fundamental astrophysical plasma processes on a vast range of scales. Commission 49 of the International Astronomical Union is devoted to the study of the heliosphere and the plasma processes therein. Traditionally Commission 49 has worked with other IAU Commissions on solar-heliosphere relations, solar wind-planet/comet interactions, and the solar wind-interstellar medium interaction. During the last few years, we have aimed to improve communications between the members of Commission 49 and the plasma physicists in other areas of astrophysics. To that end, this Report focuses on the plasma processes in the heliosphere. The report consists of two reviews: “MHD Flows in the Heliosphere” by S. Suess, which emphasizes the large-scale processes; and “Plasma Processes in the Heliosphere” by F. Verheest, which emphasizes the small-scale processes. These reviews and the accompanying bibliographies should be valuable to plasma physicists in many different fields as a source of ideas and as a guide to the recent heliospheric plasma physics literature. Copies of the Report can be obtained by writing to me at NASA/GSFC; Code 692; Greenbelt, MD 20771, USA.

In this review a few plasma processes in the heliosphere are highlighted. Undoubtedly the major event from mid-1987 to mid-1990 was the Voyager 2 fly by of Neptune on 25 August 1989, of which results are now becoming available. However, most papers dealt with the processing and interpretation of the results from the fly by of Uranus (on 24 January 1986), as well as from earlier encounters with Jupiter and Saturn. Similarly, there continued to be great interest in results from the spacecraft missions to comets P/Giacobini-Zinner and P/Halley in 1985-1986. Mention should also be made of the Phobos missions to Mars and its satellites which yielded valuable scientific results, though unfortunately prematurely aborted. Of necessity, only recent literature will be cited, as these references include earlier ones.

In the recent years, science have become able to give more definite answers to the questions of the abundance of planetary systems, of the pathways of chemical evolution leading to the emergence of simple self-reproducing structures, to the origins of life within and beyond the Solar System. At the same time a new question has been raised: the duration of life-sustaining environment, what is a prerequisit for the emergence of technology. Thanks to the fast progress of computer technology, the search for intelligent radio signals has become affordable. The number of observatories participating in this venture increases rapidly. Preparations are in progress for a large scale systematic survey.