Division IV organises astronomers studying the characterisation, interior and atmospheric structure, and evolution of stars of all masses, ages, and chemical compositions. The Executive Committee of the Division comprises the Presidents of the Five Commissions of the Division, and the Past Division President.

One of the main tasks of the Division is to advise the Executive Committee of the IAU on meetings proposed by members of the IAU. Members wishing to seek IAU support for proposed scientific meetings should follow the IAU rules for such meetings.

The Working Group on Hot Massive Stars has been officially recognized by the IAU Executive Committee during the XXIII General Assembly in August 1997. Its origins are the Hot Star Newsletter, launched in 1994, and a long tradition of interaction and collaborative research strengthened by a series of meetings on hot beaches. It gathers over 500 researchers working on OB stars, Luminous Blue Variables, Wolf-Rayet stars, and in general all topics related to the evolution of massive stars and to the physics and consequences of winds from hot stars. The very successful recent symposium on “Wolf-Rayet phenomena in massive stars and starburst galaxies” is an indicator of the increasing interest of the extragalactic community in the study of these extraordinary stars.

This triennial report (1996-1999) reviews the subject from a somewhat personal angle, mostly related to binary star formation and young binary star populations – a subject whose time had come in the early 1990s and is now in full swing.

Many astronomers have searched for binary systems among main-sequence stars, and two large-scale surveys published in 1991 and 1992 have already become classics. Well before they became famous for finding extrasolar planets (see below), observing teams led by Michel Mayor (Geneva Observatory) and Geoffrey Marcy (San Francisco State Univ., now Univ. of Calif, at Berkeley) spent many years searching for low-mass stellar companions of nearby stars. The late Antoine Duquennoy and Mayor surveyed all solar-type dwarfs (spectral types F7 through G9) within 20 pc of the Sun, while Debra Fischer and Marcy studied stars with somewhat lower mass (M dwarfs) slightly nearer to the Sun.

With an increasing wealth of data and analyses, as well as growing new areas of interest (such as spectral profiles for the search of extrasolar planets), it is no longer possible to present a comprehensive review on the area of Stellar Spectroscopy. As already stressed by the two predecessors as presidents of this Commission, Drs. D.L. Lambert and M.S. Bessell, the Astronomy & Astrophysics Abstracts and Institute for Scientific Information, NASA-ADS, Simbad databases, NIST spectroscopic database, among others, imply that these IAU reviews can now be seen as a guide to the field, presenting a survey of a variety of topics, providing no thorough coverage on each of them. A partial list of Proceedings, including topics related to Commission 29, is provided below.

Our Commission decided to proceed as before, with a rather comprehensive report, while focusing on the subjects where most progress has been achieved during the past three years. The colleagues who kindly contributed to it are W. Dziembowski (helio- and aster-oseismology), J. Guzik (intermediate-mass stars), G. Meynet (massive stars), G. Michaud (atomic diffusion), D. VandenBerg (low mass stars), G. Vauclair (white dwarfs), J.-P. Zahn (convection, rotational mixing).

Consistently with a trend observed in recent past triennial reports, progress in the theory of stellar atmospheres continues to be made in two different directions: 1) the traditional areas of continuum and line radiation transfer, line blanketing, atomic physics and atmospheric structures controlled by the joint conditions of radiative and hydrostatic equilibrium, and 2) in areas of emerging interest such as oscillations, velocity fields, winds and mass loss, chromospheres, coronae and magnetic phenomena. Particular attention is devoted also to the accurate determination of stellar elemental abundances and their implications for stellar interior structure and evolution as well as for the chemical enrichment of the Galaxy.

This report does not intend to give a complete review of all the papers that appeared since the previous General Assembly but to focus on a few subjects only.

The JD 16 was held on August 25, 1997 as one-day session with the title of “Spectroscopy with Large Telescope of Chemically Peculiar Stars”. It was supported by the Division IV and Commissions 14, 27, 29, 36, and 45.

The members of SOC were: G. Alecian, J. Babel, M. Gerbaldi, R. O. Gray, G. Mathys, P. North, M. Takada-Hidai (Chairperson), and J. Zverko (Co-chairperson).

15 talks and 18 contributed posters were presented on six topics of (1) model atmospheres and atomic data, (2) stellar parameters, (3) LTE and NLTE abundance analyses, (4) diffusion processes, (5) magnetic fields, and (6) variabilities. Approximate number of participants amounted to 50 at maximum.

This report covers the period July 1, 1996 (the closing date of the reports in the IAU Trans. 23A) through August 31, 1999. Since the reports of Commissions 27 and 42 that follow highlight the research made in the triennium, we limit ourselves here to organizational activities of the Division. The first three sections are devoted to the General Catalogue of Variable Stars (GCVS), the Information Bulletin on Variable Stars (IBVS), and the Archives of Unpublished Observations of Variable Stars, the important projects that serve us all. I am indebted to the authors, listed in the sections headings, for providing these summaries. The problems of naming and classifying variable stars, implicit in Sect. 2, are taken up in Sect. 5. The last section lists meetings sponsored by the Division.

For Commission 27 these triennial reports have traditionally been very compact literature reviews of all the fields relevant to our commission. For several triennia we have been discussing the relevance of them, and asking just who their readership is. It seems that only a few people read them, and fewer use them as introductions to the subject – supposedly one of their prime purposes. The major beneficiaries have been the writers, who have been forced to do three-year reviews of their subjects. The IAU EC gave us the option this triennium of a shorter, four-page report to which the majority of the SOC agreed.

This is the last triennial report of Commission 42 for this millennium. A great deal has been accomplished in the study of Close Binary Stars (CBS) since the discovery of the first close (eclipsing) binary, Algol, in 1783 by John Goodricke. Now, over 10,000 CBS (most eclipsing variables) are known. More than 5000 of these CBS were discovered over the last several years alone! And many more are expected to be detected over the next few years. Most of these stars were found as spin-offs of microlensing surveys. Interestingly, nearly half of these stars are found outside our Galaxy, primarily in the Magellanic Clouds and M31. Every type of star is represented as a member of a close binary. These include main sequence (as well as pre-main sequence) stars, giants, and supergiants, with the entire possible range of of spectral types and masses represented. Moreover, “dying” stars and “dead” stars, such as white dwarfs, neutron stars, black holes, and, more recently, even brown dwarfs and giant planets (e.g., 51 Peg) have been found as members of close binary systems.

Division VI of the International Astronomical Union deals with Interstellar Matter, and incorporates Commission 34. It gathers astronomers studying the diffuse matter in space between the stars, ranging from primordial intergalactic clouds via dust and neutral and ionised gas in galaxies to the densest molecular clouds and the processes by which stars are formed. There are approximately 730 members. The working groups in Planetary Nebulae and Cosmochemistry have served us well in organising periodic seminars in these subject areas. However, the Organising Committee has recognised that other developing areas of the ISM are not properly represented in the current organisation. In January 1997, the Division formed a new ISM working group on Star Forming Regions including cross-divisional representation to monitor progress in their fields and to help develop proposals for future IAU Symposia or Colloquia. In the future, especially in view of the rapid developments in spaceborne X-ray and IR astronomy, Division VI also hopes to form other working groups on the Hot ISM and the Extragalactic ISM.

The field of Molecular Astrophysics or “Astrochemistry” has grown considerably since its inception in the late 1930’s. Molecules have been observed in astronomical environments as diverse as comets in the solar system and galaxies at the highest redshifts. The common thread in these studies is that molecules are excellent probes of the physical structure and dynamics of such regions, owing to the complexity of their energy level structure and the resulting emission and absorption spectra. In addition, the chemical characteristics provide a powerful tool to study the evolution of astrophysical regions. Molecules also play an active role in the energy balance of clouds. Interstellar space is a unique laboratory in which chemical processes can occur that are not normally found on Earth. Indeed, astrochemistry is a highly interdisciplinary subject, linking the macrocosm (galaxies, stars, planets) with the microcosm (basic chemical processes and spectroscopy). The increased potential of ground- and space-based observational facilities over the full wavelength range provides a wealth of information about the physical environments in which molecules occur and makes it possible to study the development of molecular complexity throughout the Universe.

The scientific interests of Division VII are concerned with the Galactic system. Its two constituent commissions are Commission 33 (Structure and Dynamics of the Galactic System) and Commission 37 (Star Clusters and Associations). Please refer to the reports of these two commissions for the scientific highlights and lists of major conferences in this area.

Study of the Galactic system involves a wide range of astrophysics and astronomical techniques, and the fields covered by many other commissions are therefore of very significant interest to Division VII. In particular, astronomers with interests in the Galactic system could consider reading also the reports of Commissions 5, 7, 24-30, 34-36, 40, 44 and 45, among others.

This report lists some of the major conferences that took place or were published during the current period in the areas of interest to Commission 33. It then presents in summary form some of the scientific highlights in these areas. An expanded version of this report, including more related conferences, full references and a report of activities from the former Soviet Union, appears on the mid-2000 WWW page of the Commission: http://msowww.anu.edu.au/~ kcf/kcf_ftp/IAU/comm33report_1999.html.

With the exception of the activities associated with the XXIII IAU General Assembly in Kyoto, Japan, in August 1997, the report period (July 1, 1996 through June 30, 1999) has been a relatively quiet one for Commission 37. Commission activities have been restricted primarily to the consideration of proposals for IAU Symposia and Colloquia together with some activity related to cluster nomenclature issues. At the General Assembly the commission was involved in either supporting or co-supporting four Joint Discussion sessions and one of the accompanying Symposia. Eighteen new members were added to the commission, increasing membership by just under 10%.

The fields of research covered by Division VIII and its two Commissions have experienced remarkable progress over the last several years. This is due at least in part to the proliferation of major new observational facilities, and the addition of the several 8-m class telescopes presently being completed and new space facilities which will have a huge impact in the years to come. Many of the important recent scientific developments are summarized on the following pages in the reports of Commission 28 and Commission 47. These reports have been prepared in the “short” form, and are intended both to present the major scientific highlights and the most important conference proceedings and reviews for further reading.

This report covers the period July 1996 to June 1999. It has been prepared by the President of the Commission with contributions from the members of the Organizing Committee and Dr. E.M. Corsini. As discussed in Kyoto and decided by the Organizing Committee, the report is meant to be in the “short” version.

Cosmology is one of the most dynamically evolving areas of astrophysics today. Twenty years ago the estimates of the amplitude of the primordial fluctuations were about 10-3, almost a factor of 100 off of today’s measurements. Ten years ago we could only hope for high precision measurements of large scale structure, there were less than 5000 redshifts measured, and only a handful of normal galaxies with z > 1 were known. Computer models of structure formation had just begun to consider non-power-law spectra based on physical models like hot/cold dark matter. As a consequence there was considerable freedom in adjusting parameters in the various galaxy formation scenarios. In contrast, many of today’s debates are about factors of 2 and soon we will be arguing about 10% differences. The Harrison-Zeldovich shape of the primordial fluctuation spectrum, first derived from philosophical arguments can now be quantified from detections of fluctuations by COBE. The number of available redshifts is beyond 50,000, and soon we will have redshift surveys surpassing 1 million galaxies. N-body simulations are becoming more sophisticated, of higher resolution, and incorporating complex gas dynamics.

Division IX provides a forum for astronomers engaged in the innovation, development, and calibration of optical instrumentation and observational procedures, including data processing. The Reports of Commissions 9, 25 and 30 highlight the research topics covered from 1996 to 1999. Two Working Groups are associated with Comm. 9, viz. the Working Group on Sky Surveys, and the Working Group on Detectors; Commission 25 has one Working Group dealing with Infrared Astronomy. For a detailed account of progress over the last triennium, we refer to the following Reports of Commissions and Working Groups.