This report will try to review briefly the work achieved from 1982 to 1984 in different “subjects to be considered by Commission 31 Time” as adopted in Grenoble 1976. It contains also information provided by Commission members, for which hearty thanks are to be given. The limitation of space required the abbrevation of some institution reports.

Several authors have contributed to this report: L. Blitz (Section V), W.B. Burton (Sections IIIB and IVB), J. Einasto (Section VII), B. Fuchs (Sections VIC and VID), W. Hermsen (Section VIF), G. Lynga (Sections IIIA and IVA), M. Mayor (Section II), M. Miyamoto (Sections VIB and VIE) and R. Wielen (Sections I, VIA, and editing). The layout of this report follows previous practice. The galactic center is included in Sections IV and V. The references are, as far as possible, coded by their numbers (VV.CCC.NNN) in the bibliography “Astronomy and Astrophysics Abstracts” (AAA). VV identifies the volume of AAA, while CCC.NNN gives the subject category and the serial number within that volume.

This section contains work dealing with the Milky Way characteristics in the solar neighbourhood and supported by observations with wavelengths shorter than 1 mm. Thus, results are collected from gamma-ray, X-ray, UV, optical and IR observations in the different subsections. These are (1) the volume closest to the sun, (2) more distant objects at low galactic latitudes, and (3) objects at high galactic latitudes. Overall properties of the Galaxy and evolutionary effects are presented in Section IV.

Several regional surveys of southern HI made with the Argentine 100-m telescope were published (30.155.031). HI and other data were used by Dolidze (30.155. 044) to study the local distribution of gas and star forming regions. The Perseus arm region was the subject of an analogous study by Gerasimenko (34.155.139). Vallée (34.155.005) used rotation measure data from extragalactic sources in the direction of the Perseus arm to determine the magnetic field structure there and to constrain gravitational collapse theories of magnetic compression. HI in the direction of the Puppis window was surveyed by Stacy and Jackson (32.131.277) and used to study the turbulent characteristics of the interstellar medium. HI related to Gould“s Belt was studied by Pöppel and Olano (32.155.024, 33.155.030). Salter (34. 131.014) reviewed radio and other observations pertaining tc Loop I, the North Polar Spur, and considered the influence which this structure might have on the local medium.

Wollman et al. (32.155.001) present high-resolution 2 um spectra of three red giant stars in the core of the Galaxy. The properties of 0H/IR stars were studied by Baud et al. (29.131.023), Olnon et al. (29.155.032), Habing et al. (34.155.048), and Baud (34.155.042). Vanderspeck and Ricker (34.041.001) determined absolute coordinates for 19 stars within 2’ of the galactic center for epoch 1958.3 and 1976.3 and calculated their proper motions. Mould (33.155.013) obtained the radial-velocity dispersion for M stars in the nuclear bulge.

Reviews of implications of the recent observational data concerning the galactic structure were given by Bok (33.013.022) and Blitz et al. (33.155.115).

The recent data of the rotational velocity in the Galaxy were discussed by Blitz (33.155.023) and Knapp (33.155.053). A method to derive the circular velocity at the sun was proposed by Lynden-Bell and Frenk (30.155.053).

The spiral structure of galaxies is probably related to density waves, primarily governed by gravitational forces. Density waves may result from an inherent instability of galaxies against spiral perturbations as conceived in the conventional density-wave theory or may be forced by other internal or external perturbations of the gravitational field, such as neighbouring galaxies or oval distortions and bars in the inner regions of the galaxies. Reviews of recent developments on the various aspects of gravitational theories of spiral structure have been given by Ambastha and Varma (30.151.029), Athanassoula (33.151.051, 1984), Contopoulos (32.151.021, 34.151.103), Donner (30.151.085), Hunter (34.151.053), James and Wilkinson (29.151.023), Kalnajs (33.151.024), Kormendy (32.151.049), Lin (32.151.040, 33.151.025, 33.151.071), Lin and Bertin (30.151.068, 1984), Lin and Roberts (30.151.045), Martinet (30.151.043), McElroy (34.157.160), Norman (33. 157.088), Pasha and Tsitsin (34.151.042), Sorensen (29.151.024), Thonnard (31.158. 357), and Toomre (30.151.021). Seiden and Gerola (31.151.084) reviewed the theory of formation of spiral structures by stochastic self-propagating star formation in galaxies.

The global stability of galactic disks against various kinds of instabilities and oscillations have been analyzed by Abramyan (32.151.085), Aoki (37.151.053), Caimmi and Dallaporta (32.151.012), Chalov (32.151.083), Durisen and Bacon (29.151. 059), Hachisu (32.151.047), Ishibashi and Ando (37.151.055), lye (37.151.028), lye, Ueda, Noguchi and Aoki (33.151.028, 1984), Morozov (29.151.047), Nishida, Yoshizawa, Watanabe and Inagaki (30.151.084), Nishimoto (33.151.095), Nuritdinov (29.151. 083), Tajima (29.151.095), Vandervoort and Welty (29.151.077), Vandervoort (31.151. 044, 32.151.022, 34.151.055), Watanabe, Inagaki, Nishida and Tanaka (30.151.083), Wiegandt (31.151.023, 31.151.024), and de Zeeuw, Franx, Meys, Brink and Habing (33. 151.053). Local stability criteria which take into account the multi-component nature of galactic disks have been developed by Abramyan (33.151.076), Balbus (33. 151.111), Churilov and Shukhman (29.151.048), Grishchuck and Zeldovich (29.151.082), Grivnev, Ivannikova and Maksumov (1984), Jog and Solomon (37.151.013, 37.151.014), Morozov (29.151.009), Ogorodnikov and Osipkov (1980), and Polyachenko and Fridman (29.151.011).

Computer simulations provide a powerful tool for investigating the evolution of gravitating systems.

During the triennium under review many papers reported on studies of the structure of the galactic magnetic field. Andreasyan used rotation measures (RM) of large samples of extra-galactic radio sources and pulsars (29.156.001) or radio sources (32.156.002), and Inoue and Tabara (31.156.011) used in addition optical polarization of stars to investigate the direction of the large-scale regular magnetic field. Thomson and Nelson analyse the RMs of 459 extragalactic sources (32. 161.001) to determine the best fit parameters for a galactic magnetic-field model, and find agreement with their earlier work using pulsars (27.156.009). Similarly, Sofue and Fujimoto (33.155.011) show that the characteristic features of the RM distribution on the sky are well reproduced by a model in which the magnetic field is in a bisymmetric, two-armed logarithmic spiral configuration. Finally, Welter, Perry and Kronberg (37.159.096) present a statistical analysis of the (Galaxy-corrected) residual rotation measure (RRM) of 116 QSOs.

It has become more evident during the last three years that the study of interstellar matter is paramount to understand the evolution of the universe and its constituents. From observations of the present state of the interstellar medium, in our galaxy, in other galaxies, and between galaxies, it is possible to test theories of: evolution of the universe, formation and evolution of galaxies, formation and evolution of stars and of the evolution of the interstellar medium itself. The amount of information on the interstellar medium that has been gathered during the 1982-1984 period has been very large and the theoretical models that have been ellaborated to explain these observations have been very numerous, these facts show that the subject of our Commission constitutes a very active field of astronomical research.

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, pulsation, and explosions for the three year period from mid-1981 to mid-1984 would be excessively long. Our topics here, in order from the most massive stellar classes to the least are: Massive Stars (R.M. Humphreys), Rotation in Late Type Stars (W. Benz), Helioseismology (J. Christensen-Dalsgaard), Planetary Nebula Central Stars (E.M. Sion), Pulsations in Hot Degenerate Dwarf Stars (A.N. Cox and S.D. Kawaler), and White Dwarfs (V. Weidemann). There is some overlap in the reviewing of these last three reports because the topics are very closely related. Concentration in this dying stage of stellar evolution seems appropriate because of the great current interest in these matters.

Commission 36 acts as a sponsor or co-sponsor at the following symposi and colloquia: IAU Colloquium No. 90 “Upper Main Sequence Stars with Anomalous Abundances”, Crima, USSR (May 1985), IAU Colloquium No. 89 “Radiation Hydrodynamics in Stars and Compact Objects”, Copenhagen, Denmark (June 1985), IAU Symposium No. 120 “Astrochemistry”, Goa, India (December 1985), IAU Colloquium No. 87 “Hydrogen Deficient Stars and Related Objects”, Bangalore, India (December 1985).

According to dynamo theories, the interaction between convection and rotation is responsible for the generation of magnetic fields in solar-type stars. Stellar observations can explore the ways the global parameters, like the surface rotation and internal structure, affect the production of magnetic fields. In this very brief review I wish to concentrate on recent progress in understanding the evolution of stellar rotation, and the dependence of stellar cycles and magnetic activity on rotation, internal structure, and age.

Wolf-Rayet (WR) stars are the helium-burning remnants of massive stars (initial mass ≲30 M©), which have lost their outer hydrogen-rich layers through the processes of Roche lobe overflow to a companion or mass loss by a strong stellar wind. The characteristic emission-line spectrum which defines the WR spectral type is produced by a stellar wind that is so dense and opaque, that the radiation of all lines and continua arise from material in the wind. Because the wind completely screens any radiation emitted by the hydrostatic core of the star, the spectra of WR stars are nearly impossible to interpret quantitatively, and the basic parameters — such as mass, luminosity, temperature, and chemical composition — are poorly determined.

The main characteristic of white dwarf atmospheres is a pressure that is at least two orders of magnitude higher than in main sequence star atmospheres of the same effective temperature. This is due to the high gravity (log g ≈ 8), extreme metal under-abundances (Δlog εM ≳ 2.5), and (in many cases) the replacement of hydrogen by helium as the main constituent. As consequences the atmospheres are very thin (ΔR ≲ a few km) and the level populations of all species are given by the Boltzmann distribution (perhaps with the exception of the extreme outer layers, Greenstein 1973, Pilachowski 1984). Thus, models can be calculated under the assumption of plane parallel radiative transfer and local thermodynamic equilibrium, which facilitates the numerics very much;but special care has to be taken of pressure effects (e.g., broadening of spectral lines, quenching of levels, changes in the dissociation-ionization equilibria). In addition, the proper consideration of convection, which is very effective and may reach into the optically thin layers, makes the construction of model atmospheres for white dwarfs rather tedious and costly.

Accretion discs are a popular ingredient among theorists for modelling a number of high energy astronomical objects like quasars, active galactic nuclei (Rees 1984) and galactic X-ray sources (Levin and van der Heuvel 1983). However, the observational evidence (as opposed to the strong theoretical presumption) that accretion discs exist in these objects is weak, and in only one case has some attempt been made to argue the case for a disc on the basis of its spectral properties (Malkan 1983). Indeed the structure of accretion discs is sufficiently ill-understood that any progress in this area must rest on a strong interaction between theoretical modelling and the actual observation of accretion discs in action.

The last three years have been very productive for cluster research. This report, on activities in the field, has been compiled by the members of Commission 37. It begins with sections on recent meetings, and on data catalogs (G. Lynga). Detailed tables of work on associations (P.E. Nissen), open clusters (G.L.H. Harris) and globular clusters (R.E. White) are then given. A section on cluster dynamics (D.C. Heggie) follows, and the final section concerns present trends in cluster research (C. Pilachowski).

While the chief function and methods of operation of the Commission have remained much the same as in the past, there has been a gradual evolution in the nature of the proposals submitted. A greater fraction now come from countries in which the study of astronomy on a professional basis is as yet very recent and more proposals are being received from relatively young astronomers, although admittedly the distinction between a “young” and an “established” astronomer is not always easy to make. The commission may wish to consider whether or not it is advisable to reconsider its guidelines. Grants awarded during the interval 30 November 1981 and 31 January 1985 were the following.

The last triennium marked the 50th anniversary of the paper describing the first observations of cosmic radio emission by Karl Jansky in 1933. Sullivan (82 Classics in Radio Astronomy, Reidel) has published a collection of the major historical papers in radio astronomy, and collections of papers discussing the historical development have been published by Sullivan (84 Early Years of Radio Astronomy, Cambridge Univ. Press) and by Kellermann and Sheets (84 Serendipitous Discoveries in Radio Astronomy, NRAO).