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).