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.