We have taken part to an exceptionally rich colloquium, characterized by a large amount of information in all fields of physics, and a remarkable collection of observational data. Our understanding of what is going on inside the stars has changed in a radical manner during the last years, on one side because the observations are bringing new kinds of information, and on the other side because theory in its development is taking into account a number of processes, some of them having been completely ignored only ten years ago.

It is impossible to draw here a complete list of problems. There are many cases where some inconsistency could be found in the theory itself or some contradiction between observational data and theory. I recommended that such a list should be drawn carefully. The participants to the round table discussion will give their contribution, helping to open the way to new fields of research and to new discoveries.

As it is impossible to approach all the problems concerning the inside of the Sun, a number of questions will not be taken into consideration during the meeting. In this brief overview of the presently unsolved questions I shall insist on some special aspects of the solar properties: the variations of the solar radius, the generation of the solar wind, some interesting effects due to the presence of a strong gradient of 3He, the history of the rotating Sun. The presence of the planetary system suggests that the Sun might have been a T Tauri star, with an accretion disc and may have started on the mains sequence as a fast rotating star. A sketch is given of the possible consequences.

The GALLEX collaboration aims at the detection of solar neutrinos in a radiochemical experiment employing 30 tons of Gallium in form of concentrated aqueous Gallium-chloride solution. The detector is primarily sensitive to the otherwise inaccessible pp-neutrinos. Details of the experiment have been repeatedly described before [1-7]. Here we report the present status of implementation in the Laboratori Nazionali del Gran Sasso (Italy). So far, 12.2 tons of Gallium are at hand. The present status of development allows to start the first full scale run at the time when 30 tons of Gallium become available. This date is expected to be January, 1990.

The place of stellar physics in Astrophysics is not the same as it were 50 years ago. Stellar evolution theory has been one of the preferred places of numerical calculations, and as a consequence, standard evolution models, from the homogeneous pre-main sequence star to the final stages, white dwarfs, neutron stars, supernovae, has become sort of archetype of numerical analysis and computation, the essence of perfection.

The absence of concensus on several of the problems which have been discussed during the meeting is perhaps the best demonstration of the usefulness of the Symposium.

We consider stellar evolution in low mass stars (1–3 Mo) near the main sequence with the hypothesis that mild turbulence is present within the all star. Turbulent transport of the elements is modeled by diffusion equations where the diffusion coefficient is chosen to be D = R✶eν where ν is the kinematical viscosity and R✶e is a Reynolds number. We consider the effects of the growth of the gradient of the mean molecular weight on turbulence. The main consequences of diffusion on stellar evolution are (1) an increase of the life time near the main sequence and (2) a change of the radial distributions of chemical species (12C, 13C, 14N, 160) (figure 1). The inhibition of the turbulence, when the gradient of mean molecular weight reaches a certain critical value, allows the evolution towards the red giant branch. When stars evolve towards the giant branch, chemical species are dredged up to the surface. At this stage models with and without diffusion, predict substantially different surface abundances (in particular the 12C/13C and C/N ratios). Comparison between models and the available data on giants during the first dredge-up show that abundance anomalies can be explained if turbulent mixing is present during the main sequence phase (figure 2).

After the first suggestion by Schatzman (1963) that accreting white dwarfs, close to the limiting mass, might be the progenitors of type I Supernovae, the problem was not studied until Schatzman (1974) described the competition between collapse dominated by beta decay, which would lead to neutron star formation and collapse dominated by nuclear reactions leading to stellar disruption.

The presence of a mild turbulence inside rotating stars has been considered by Howard et al (1967) and by Bretherton et al (1968) in connection with the problem of the solar flattening, raised by Dicke (1970). The possibility of using abundance determination to test the existence of that turbulence has been considered by Schatzman (1969).

A summary of the main results and problems concerning explosive and eruptive stars is given. The way in which the observations are related to the internal structure problems is briefly explained. Suggestions for further work are made: (1) dynamo theory, supersonic turbulence, stability of the envelope of T Tau stars; (2) rate of exchange of matter in close binary as the final clue to the thermal runaway theory of novae.

During the 13th IAU General Assembly in Prague it was decided that each nation adhering to the IAU should be represented in Commission 46 by one member interested in the teaching of Astronomy. Six nations were already represented by the members of the Organizing Committee. For all other nations the Commission President contacted the head of the National Delegations to the IAU with the request to designate one IAU member of the particular country as member of Commission 46. With only a few exceptions every IAU member nation designated a representative in this Commission which now contains representatives of 33 nations. It is hoped that the missing nations in our Commission will also soon be represented by an IAU member active in the promotion of Astronomy education. Each member is responsible to (a) promote the teaching of Astronomy in his own country, (b) to keep in touch with the Astronomy teachers of his country, and (c) to communicate to the Commission President any programs and developments, problems and needs concerned with Astronomy education in his country. It is also hoped that institutions in countries not yet adhering to the IAU but which might wish to start some Astronomy teaching, could contact the Commission and, in some specific cases, could designate a Consulting Member to the Commission.

During the period under review, theoretical work in the field of stellar constitution and evolution of stars has been effectively continued by several teams permanently working in Belgium, Denmark, France, German Democratic Republic, German Federal Republic, Italy, Japan, Poland, the United Kingdom, the U.S.A., the U.S.S.R. as well as by individual scientists in Argentina, Bulgaria, Czechoslovakia, India, Sweden and others. Most attention has been given during the past three years to analysis of late stages of stellar evolution, rotation, evolution of binaries, loss of mass on various stages of evolution, stellar stability, neutrino astrophysics, physical processes in the presupernovae stage. The discovery of pulsars has raised extremely the general interest for white dwarfs and neutron stars, and consequently the number of papers with new hypotheses concerning quasi-stellar sources has substantially dropped.

Many new evolutionary sequences of stellar models for various masses and different chemical compositions have been computed using improved numerical techniques and large computing programs. It is regretted that many of these results are difficult to compare mainly because of the differences in the input physics and the way the numerical results are being published. This is a field in which a closer international co-operation is highly desirable, especially on the following points: exchange of ideas on the programs presently under way and the planned programs in order to avoid unnecessary duplications: agreement on the numerical results which should be published; exchange of technical informations: (input physics, computing methods, detailed results of computations, opacity tables, etc.). Several attempts in this direction have been undertaken during the period under review (for example, Commission 35 Circular Letters NN 1–7 containing information on current work, publication by the U.S.S.R. Academy of Sciences of the Cox and Stewart’s Opacity Tables for 23 mixtures, several joint international projects for using the same programs, etc.), but the problem still remains to be solved.

There is astrophysical evidence for the existence of shocks propagating in regions of variable density. We have therefore the choice of discussing first the physics of shocks in a variable density atmosphere, or the astrophysical phenomena. Following Kaplan's preliminary report, we shall describe first the astrophysical facts, for the reader to be able to understand the connection of the physics with the astrophysics.

Strong radio emissions are associated with solar flares. It seems worth while, therefore, to examine whether radio emission associated with flares and eruptions in nonstable stars could be observed. The first problem in this respect is establishing the threshold of sensitivity necessary to receive anything during an eruption or a flare; the second one is naturally fixing the duration of the radio emission, which can be much shorter in a given wavelength than the optical emission.

Deux mécanismes importants de perte de masse s'accompagnent d'une grande perte de moment angulaire:

1. 1° une étoile en contraction et en rotation peut perdre de la matière le long de son équateur. Sa vitesse de rotation est alors telle qu'à l'équateur la gravité et la force centrifuge s'éuilibrent;

2. 2° l'étoile peut perdre de la matière par des processus éruptifs. La perte de moment angulaire est d'un ordre de grandeur très différent suivant que la matière éjectée est ou non guidée par les lignes de force d'un champ magnétique.

One seeks the condition of spontaneous collapse of a layer of interstellar matter by the method of marginal stability. The radiation field is included in this treatment of the gas-dynamic properties of the interstellar material. The optical model used is that of Ambartsumian's, which neglects interlocking.