This subsection reports results on the existence and nature of the possible unseen matter near the Sun, the local density of disc and halo stars, the respective luminosity functions and the local distributions of some special type objects. It summarizes work relating to the space density of stars of different types in the plane of the Galaxy and dealing with photometric stellar studies in the Milky Way fields of strong interstellar extinction. It also reviews galactic models relevant to the local structure.

The local interstellar medium was the subject of a meeting held in Madison Wisconsin in June 1984. Much of the discussion centered around the structure of the local interstellar medium (LISM). Results presented at the meeting included observations of the very local interstellar medium within a parsec of the sun probed by spacecraft using backscattered solar radiation (38.131.240, 38.131.241). The diffuse warm gas in the LISM has been explored by a variety of means including various UV and optical absorption lines (38.131.243), chromospheric Lyman α (38.131.245), Mg I and Mg II (38.131.246, 38.131.247, 38.131.248, 38.131.249, 39.131.004), Hα emission (38.131.254) and Na (38.131.255, 38.131.256, 38.131.257). Other probes of the diffuse gas come from hot DA dwarfs (38.131.253), EUV and continuum absorption (38.131.263), observations of β Canis Majoris (38.131.250), and HI and radiocontinuum observations (38.131.273). The surprising existence of a cold component is inferred from CO observations (38.131.267) and possibly from extinction maps (38.131.258, 38.131.260, 38.131.266). The hot component is seen by means of soft X-rays (38.131.265, 38.131.280), Fe XIV (38.131.264), and OIV lines (38.131.262). An observational overview was presented by York and Frisch (38.131.244) and Cowie presented a theoretical model of the LISM as a supernova remnant (38.131.279).

The previous report on structure and dynamics of the galactic system was given by Wielen (41.155.100). The recently recommended values for solar distance to the galactic center (8.5 kpc) and our rotation speed around it (220 km.s-1) were discussed by Trimble (42.155.043).

The distance scale of the Galaxy was reviewed by Barkhatova et al. (40.155.088). A discussion of typical corrugation scales in the Galaxy was given by Spicker and Feitsinger (42.155.003), who concluded that three distinct scales seem to exist: 1-2 kpc, 4-8 kpc, and > 13 kpc. These corrugations are reflected in the distribution of O and B-stars and HII regions, and to a lesser extent in the HI distribution. Feitzinger and Spicker (39.155.026) investigated the corrugation phenomenon for the (heliocentric) longitude range 10° ≤ l ≤ 240° as derived from HI studies.

One of the highlights of the study of the galactic environment is the demonstration that companions and hydrogen clouds surrounding our Galaxy form a ring-like structure similar to that surrounding external polar-ring galaxies. Probably this feature is common in giant galaxies. Dwarf galaxies may possess their own dark coronas, which fact, if confirmed, puts severe constraints on the nature of dark matter. Available evidence confirms earlier suggestions that our Galaxy with its massive corona, companions, and surrounding gas forms a single system with many mutual interactions. Most companions of our Galaxy as well as the main hydrogen streams are located in a narrow strip inclined 70° to the galactic plane.

The interest in stellar orbits focussed on two areas: Firstly, on the existence of non-classical integrals of motion (“third integral”) and on the occurence of stochastic or chaotic motions in systems with two or three degrees of freedom. While the case of three degrees of freedom is the more realistic one, results on systems with only two degrees of freedom can be applied to situations such as the motions of stars in the co-moving meridional plane of axisymmetric galaxies or in the equatorial plane of spiral or barred galaxies. Secondly, there is continuing interest in the orbital motions of stars in triaxial systems, which may represent either triaxial elliptical galaxies or galactic bars. The ultimate aim of many of the studies on stellar orbits is to build self-consistent models of stellar systems on the basis of the individual orbits of the stars.

Reviews on numerical methodes for simulating gravitating have been given by Aarseth (42.151.078), Saslaw (40.003.011), Anosova (40.042.119), Tajima, Clark, Craddock, Gilden, Leung, Li, Robertson, and Saltzman 41.151.104), Contopoulos and Magnenat (41.151.086), Martinet and Pfenniger (43.151.034, 43.151.100), and Pfenniger (40.151.025, 43.151.092).

During the triennium under review some proceedings and books have been published in the USSR concerning the field of galactic research. Among them there are the proceedings of the international colloquium “Stellar Catalogues: Data Compilation, Analysis, Scientific Results”, held in Tbilisi, USSR, 10-15 September, 1984 (Kharadze and Kogoshvili, 1985), and “Problems of Astrometry” (Podobed, 1984). A number of books were published: “The Galaxy” (Marochnik and Suchkov, 1984), “Physics of Gravitating Systems”, volumes I and II (Pridman and Polyachenko, 1984ab), “Stellar Astronomy” (Agekyan, 1985), “Magnetic Fields in Space” (Bochkarev, 1985), “Methods in the Qualitative Theory of Dynamical Systems in Astrophysics and Dynamics” (Bogyavlensky, 1985), “Supernovae and Stellar Wind: Interaction with the Gas of the Galaxy” (Lozinskaya, 1986).

The previous report started with optimistic remarks about the increasing importance of the study of interstellar matter in astronomy. This trend has largely been confirmed in the 1985-87 period and it is clear that the subject of our Commission is one of the most active fields of astronomical research. This is also shown by the rapidly growing number of members and by the constitution of new working groups. The major new event in the period has undoubtly been the availability of IRAS data.

This report of Commission 35, as in past reports, consists of some details of only a few selected topics. This is necessary because a survey of the entire field of stellar formation, structure, stability, evolution, explosion, and nucleosynthesis for the three year period from mid-1984 to mid-1987 would be excessively long. Our topics here, in order from early to late evolutionary pahses are: Convective Overshooting (N.H. Baker), Mass Loss (I. Appenzeller), Novae (M. Livio), Presupernova Models and SN1987A (K. Nomoto), and Structure of X-Ray Bursting Neutron Stars (M.Y. Fujimoto and D. Sugimoto). In addition, Asteroseismology (H. Shibahashi) is reported briefly as one of the new disciplines now being developed. About two decades ago, Professor Martin Schwarzschild suggested convection, mass loss, and calculation of models through supernova stage as ones of the most important problems to attack. Though great progress has been achieved in these topics, we still have some fundamental questions concerning physical mechanisms involved. This is the reason why these topics are selected for this report.

Commission 36 acted or acts as a sponsor or a cosponsor of the following Symposia and Colloquia.

(l)Symposium No. 122: “Circumstellar Matter”, Heidelberg, FRG (June 1986), (2)Symposium No. 132: “The Impact of Very High S/N Spectroscopy on Stellar Physics”, Paris, France (June 1987), (3)Colloquium No. 95: “Second Conference on Faint Blue Stars”, Tucson, AZ, USA (May 1987), (4)Colloquium No. 102: “UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas”, Beaulieu-sur-Mer, France (September 1987), (5) Colloquium No. 106: “Evolution of Peculiar Red Giant Stars”, Bloomington, IN, USA (July 1988), (6)Colloquium No. 108: “Atmospheric Diagnostics of Stellar Evolution: Chemical Peculiarity, Mass Loss and Explosion”, Tokyo, Japan (September 1987).

The last three years have been very productive for cluster research, especially now that observations with CCDs have become so routine. After a section on recent meetings, and one on data catalogues (by J.-C. Mermilliod), subsequent sections of this report go into details on individual topics: associations (P.E. Nissen), open clusters (G.L.H. Harris), globular clusters and cluster systems (R.E. White) and dynamical theory (D.C. Heggie).

The rapid growth in the volume of observational data has meant regrettably that the information has had to be tabulated in an even more compressed form than in earlier Reports. As in previous Reports, three-figure references are to Astronomy and Astrophysics Abstracts, and two-figure references to Physics Abstracts. Most entries cover publications from 1 July 1984 to 30 June 1987, but some exceptions are noted under the individual sections. For abbreviations see §6.

The present report covers the period 1 February 1985 to 30 November 1987. During this period a total of 23 travel grants were awarded as follows:

The following commission members have contributed to this report:

M Birkinshaw, R J Cohen, J J Condon, T J Cornwell, J R Dickel, P A Feldman, R Genzel, M Goss, V Kapahl, Gopal Krishna, M Kundu, A G Lyne, C R Masson, A C Readhead, W Reich, J M Riley, A J Turtle, J M van der Hulst, T L Wilson.

Commission 41 has been involved in one colloquium and one symposium since the last report:

IAU Colloquium 91 on “The History of Oriental Astronomy” was held in New Delhi, November 13-16, 1985, preceding the XlXth General Assembly. Members of the scientific organizing committee were S.M.R. Ansari, E.S. Kennedy, D. King, R. Mercier, O. Pedersen, D. Pingree, G. Saliba, Xi Ze-Zong and K. Yabuuti. The colloquium was co-sponsored by the International Union for the History and Philosophy of Science, and by a number of organizations in India: the Council of Scientific and Industrial Research, New Delhi, the Department of Science and Technology, New Delhi, the Indian Institute of Astrophysics, Bangalore, the Indian National Science Academy, New Delhi, the Tata Institute of Fundamental Research, Bombay, and the University Grants Commission, New Delhi. The local organizing committee, chaired by G. Swarup, made possible a number of local excursions, including a conducted tour of the great stone open air observatory, built in the city by the enlightened Maharadjah Jai Singh in the 18th century. The colloquium brought 84 participants from 19 countries. 46 papers were presented of which 10 were invited, covering aspects of astronomy in the far east and middle east since the earliest civilizations. Papers from Colloquium 91 have now been published in book form: History of Oriental Astronomy, G. Swarup, A.K. Bag, and K.S. Shukla, editors, Cambridge University Press, Cambridge, England, 1987. Contributions are divided into three broad categories: ancient astronomy and its characteristics, ancient elements and planetary models, and medieval astronomy. Within these are papers on the characteristics and achievements of early astronomy in the eastern half of the world, including inter-regional development and mutual influences, ancient data relating to eclipses, supernovae and comets, medieval astronomical developments, instruments and early observatories, and the interplay between observational and theoretical astronomy. A short introductory paper by the revered historian E.S. Kennedy opens the book, as it set the stage for the colloquium in New Delhi: “We find (astronomy) originating a few centuries before the Christian era in two disparate cultures, Mesopotamia and the Hellenistic world. From the Mediterranean it passed to India, there to flourish. Thence the centroid of activity moved westward, residing in the lands of Islam during medieval times, more recently in Europe. Now astronomical research is carried out throughout the entire world.”

During the XlXth General Assembly of the IAU in Delhi the number of members of Cotrmission 42 increased to 260. This simply reflects the growing interest and importance of our field. Growing is not only the number of astronomers involved in research on CBS but also the number of papers resulting from that activity. As an example one can quote the numbers of papers listed during the last few years in Sections 117 (Close Binaries), 119 (Eelipsing Binaries), and 120 (Spectroscopic Binaries) of the Astronomy and Astrophysics Abstracts: 705(1982), 775(1983), 836(1984), 1080(1985), and 911(1986); note that many additional references could be added to these numbers from other sections. Naturally, such numbers alone do not reflect the quality and even less so the position and significance of the CBS field. Here one could perhaps mention an impressive record of successful research proposals involving requests for the observing time on large, ground based telescopes and on space instruments. Indeed, in spite of a very strong competition from other fields, programs involving CBS are usually placed very high on the priority lists (cf. Sections 2D and 2E). Obviously, the close binary systems, their evolution, and the physical processes which occur in them (accretion, stellar winds, nuclear burning, etc) appear interesting and important not only to those who are involved in their studies but also to astronomers from other fields.

The tragic loss of Space Shuttle Challenger and her 7 crew members in January 1986 has seriously affected the astronomical research from space in the U.S.A. and, to a lesser extent, in Western Europe. The incident has caused setbacks in a number of space projects, including the delay in the launching of the Hubble Space Telescope. Nevertheless, the field of space astronomy remained active during the present reporting period (1984 July through 1987 June).

X-ray astronomy has continued to flourish in the three years covered by the present report (to June 1987) despite the continuing scarcity of new missions. The European EXOSAT has probably made the greatest impact during this period, carrying out over 2000 separate observations up to it’s loss of attitude control in April 1986. A major reason for the success of EXOSAT was the unusual spacecraft orbit which provided uniquely long source exposures, uninterrupted by Earth occultation, of up to 70 hours duration. The continuous light curves of many galactic and extragalactic sources have proved particularly valuable in studying details of time variability over a broad frequency range and in this respect the EXOSAT data archive is unlikely to be superceded in this century. For several months after the demise of EXOSAT, astronomers had no operational X-ray satellite for the first time since the launch of Uhuru in 1970. This unfortunate state of affairs ended in February 1987 with the successful launch of the Japanese ASTRO-C satellite. Three months later, observations began with several X-ray instruments on board the Soviet MIR space station and at the time of writing both GINGA (the post-launch name of ASTRO-C) and the MIR instruments are working well.

Results from the IUE satellite, summarized in the section which follows this one, continue to dominate the literature for research topics which rely on observations in the ultraviolet. This trend may be accentuated in the near future, as we experience the natural attrition of papers based on results from previous major missions which are no longer operating, such as TD-1, Copernicus, ANS and BUSS. The Challenger accident on January 28, 1986 abruptly halted flights of new orbital facilities which depend on the Space Shuttle and has created long and somewhat indefinite postponements in the eventual manifesting of payloads ranging in size from simple experiments in Getaway Special (GAS) and Spartan carriers, to telescopes of intermediate size on Spacelab (such as those which were to fly on the Astro mission in March 1986) to the Hubble Space Telescope. Suborbital missions, i.e., sounding-rockets and balloons, will probably dominate the extra-IUE uv astronomy scene until there is a re-establishment of a vigorous launch schedule for expendable vehicles and/or the Space Shuttle.

The period from 1984 through 1987 saw no new infrared space missions. Investigations, however, continued with airborne, balloon, and rocket activities, and follow-up analysis of data from the Infrared Astronomical Satellite (IRAS). Two major ephemeral events occurred during this time, the Comet Halley apparition and SN 1987a, the supernova in the Large Magellanic Cloud. With improved analysis on the database and follow-up observations new results have been forthcoming from IRAS. This work may help astronomers understand everything from the origin and evolution of quasars to the composition of material in cometary nuclei.

Radioastronomy can use space technology either to go close to the source of the radioemission to increase the sensitivity of the observations and have different viewing geometry, or to avoid the effect of the Earth’s environment, i.e. to extend the useful frequency range below the ionospheric cut-off of a few megahertz and at submillimeter wavelengths. A third field which will certainly develop in the future is the use of space to increase the spatial resolution of radio-interferometry for imaging radiosources.