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We describe the results of the GALLEX solar neutrino experiment after completion of the project. In particular, we summarize the results for GALLEX IV (12 solar runs) and for our 71As - spiking experiments. The integral GALLEX result for all 65 solar runs (GALLEX I–IV) is (78 ± 8) SNU (1σ). This is only slightly more than half of the expected rate. The significance of this deficit is assured. • directly by the results from our two 5Cr neutrino source experiments (at the 10% - level), and • indirectly by means of experiments in which 71Ge is generated within the target solution from beta-decaying 71As (at the percent level). GALLEX at Gran Sasso is now succeeded by Gallium Neutrino Observatory). The GNO status as of October 1998 is reported.

After 5.5 years of data taking, GALLEX ended its experimental phase. The solar neutrino production rate, 76.4 ± 8 SNU, represents about 55% of the predicted rate. The As tests prove, at the 1% level, the reliability of the technique and the detection of 51Cr neutrino, with the nominal efficiency (93.0±8%), control the response of the detector to neutrinos in the solar energy range.

Since May 1991, the GALLEX experiment — installed in the Gran Sasso Underground Laboratory — is continuously monitoring the solar neutrino signal by measuring the 71 Ge production rate in a target of 30.3 tons of nat Ga. The measured signal 77.1 ± 8.5 (stat) +4.4 – 5.4 SNU (1 σ ) [1] is well below the Standard Solar Model (SSM) prediction: ⋍ 120–130 SNU. To exclude unknown systematic effects as responsible for the observed deficit, an experiment with a (62.5 ± 0.4) PBq 51 Cr neutrino source has been performed 2. , 3. . The ratio R=0.97 ± 0.11 between measured and expected Cr-produced 71 Ge demonstrates that the deficit cannot be ascribed to unknown experimental systematics. Although astrophysical reasons could still remain as a possible explanation of the “solar neutrino puzzle”, we recall that the GALLEX result, when considered together with the results of the other solar neutrino experiments, would allow to strongly constrain the neutrino masses and mixing angles in the framework of the MSW effect.

This report confronts the different aspects of the solar interior from the experimental and theoretical points of view, discussing photospheric abundances, neutrinos and acoustic mode measurements. The theoretical approach mainly concerns the classical framework of stellar evolution, nevertheless, particle interpretation of the data and astrophysical solutions invoked in the last 10 years are coherently examined.

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.

Pre-Main-Sequence stars with masses between 2 and 5 M⊙ (Herbig Ae/Be stars) have radiative subphotospheric envelopes. However, they possess strong stellar winds and show definite signs of activity which could be linked to surface magnetic field. Therefore, they must lose angular momentum at a significant rate.

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 aim of this work is to present a transport process which is likely to have a great importance for the internal constitution of the stars.

We report the GALLEX solar neutrino results for the measuring period GALLEX III, the period from 12 October 1994-4 October 1995. Counting for these runs was completed on 29 March 1996. The GALLEX III result (14 runs) is [53.9 ± 10.6(stat.) ± 3.1 (syst.)] SNU (1σ). This is 15.8 SNU below but statistically compatible with the new combined result for GALLEX (I+II+III) (53 runs), which is [69.7 ± 6.7(stat.) −4.5 +3.9 (syst.)] SNU (1σ) or (69.7 −8.1 +7.8 ) SNU with errors quadratically added. We also give the preliminary result from our second 51 Cr-source experiment: the measured detector response is 83±10% of expectation. The combined result from both GALLEX 51 Cr-source experiments is 92±8% of expectation.

Should we approach the solar neutrinos problem having in the principle of Occam’s razor? Which means: do not introduce any new physics before being sure that the currently known physics does not work. All attempts until now have failed. A brief summary of the difficulties of the problem is presented. The phenomenological approaches of Schatzman and Maeder (1981), Berthomieu et al. (1984) and of Lebreton and Maeder (1987) are analysed. The importance of the disagreement between these last models and the results of helioseismology is discussed, and it is shown to be smaller than previously estimated. The need for another process is obvious. It is shown, according to the suggestion of Press (1981), that internal waves generated by turbulent motion in the convective zone, can behave as a new agent of mixing. Recent results obtained by Montalban and Schatzman (1993), based on a plume model suggested by Rieutord and Zahn (1993), confirm the previous results of Schatzman (1993) and of Montalban (1993). Despite radiative damping, the diffusion coefficient diverges when approaching the centre of the star, but this effect is limited by the work done by the diffusion process against the μ-gradient. Work is in progress in order to check whether the effect of this transport process is valid and can lead to a better prediction of the solar neutrino flux without being in disagreement with helioseismology data

The radiochemical GALLEX experiment, which has been measuring the solar neutrino flux since May 1991, has performed an investigation with an intense man-made 51 Cr neutrino source (61.9 ± 1.2 PBq). The source, produced via neutron irradiation of ≈ 36 kg of chromium enriched in 50 Cr, primarily emits 746 keV neutrinos. It was placed for a period of 3.5 months in the reentrant tube in the GALLEX tank, to expose the gallium chloride target to a known neutrino flux. This experiment provides the ratio, R , of the production rate of Cr-produced 71 Ge measured in these source exposures to the rate expected from the known source activity: R = 1.04 ± 0.12. This result not only constitutes the first observation of low-energy neutrinos from a terrestrial source, but also (a) provides an overall check of GALLEX, indicating that there are no significant experimental artifacts or unknown errors at the 10% level that are comparable to the 40% deficit in observed solar neutrino signal, and (b) directly demonstrates for the first time, using a man-made neutrino source, the validity of the basic principles of radiochemical methods used to detect rare events (at the level of 10 atoms or less). Because of the close similarity in neutrino energy spectra from 51 Cr and from the solar 7 Be branch, this source experiment also shows that the gallium detector is sensitive to 7 Be neutrinos with full efficiency.

The galliumchloride detector operated by the GALLEX-collaboration in the Gran Sasso Underground Laboratory responds primarily to pp-neutrinos. They are produced in the primary fusion reaction of hydrogen into deuterium and directly coupled to the solar luminosity. Standard Solar Models predict ca. 58% of the total signal expected in GALLEX (123-132 SNU) to be due to pp-neutrinos. The relative pp-neutrino dominance becomes even larger if the deficit of higher energy neutrinos (as observed in the Homestake- and Kamiokande experiments) is considered. During the first data taking period, 15 solar runs had been performed within the exposure period 14.5.1991 - 29.4.1992. The result, 81 {+-} 17 {+-} 9 SNU provided the first experimental evidence for pp-neutrinos from the Sun. At the same time, it confirmed the depression of higher energy neutrino fluxes relative to the model predictions. Here the authors report the results of 15 more solar neutrino runs, covering the period 19.8.92 - 13.10.93. They obtain 78 {+-} 13 {+-} 5 SNU. Evaluated together, the result for all 30 runs is 79 {+-} 10 {+-} 6 SNU. While the SNU rate of GALLEX I is well reproduced the statistical error has been reduced so substantially that a value of signal +2{sigma}more » is required to accommodate not only pp-and pep- but also the {sup 7}Be-neutrino induced {sup 71}Ge-production. Contrary, the fate of {sup 8}B-neutrinos has only little discernible effect on the GALLEX data. In conclusion, with the present errors GALLEX constitutes a 2.5 {sigma} problem for {sup 7}Be neutrinos within the frame of {open_quotes}astrophysical{close_quotes} solutions. Alternatively, the particle physics solution (MSW-effect) can consistently explain all available solar neutrino results, leading to a most probable mass scale with the muon-neutrino at approximately 3 meV (milli-eV). However, since the GALLEX result allows the presence of pp and pep neutrinos at full strength. the latter explanation of the data is not forced.« less

We report the solar neutrino results from the complete set of runs in the exposure period, GALLEX II, from 19 August 1992 - 23 June 1994. Counting for these runs was completed on 10 December 1994. The GALLEX II result (24 runs) is [75.2±9.7 (stat) −4.6+4.1 (syst)] SNU (1 σ). After three years of recording the solar neutrino flux with the GALLEX detector, the combined result from the 39 completed solar runs (GALLEX I+II) is [77.1±8.5 (stat) −5.4+4.4 (syst) SNU (1 σ) or 77.1 −10.1+9.6 SNU with errors combined in quadrature. The combined error (± 13%) has now approached a level where the limits on the derived contribution of 7Be neutrinos to the GALLEX signal confront the predictions of solar models.

The first period (GALLEX I) of data taking in the GALLEX solar neutrino experiment has been completed. From 14 May 1991 to 29 April 1992, the experiment observed the solar neutrino flux using neutrino capture by 71 Ga to form 71 Ge. Counting ended on 2 November 1992. The final result from the 15 runs of this periodpis (81±17 [ stat .]±9 [ syst .]) SNU (1 σ ). The first 6 runs of GALLEX II recorded the neutrino signal from 19 August 1992 to 3 February 1993. The preliminary result for this period is (97±23 [ stat .]±7 [ syst .]) SNU (1 σ ). With counting data considered until 29 April 1993, the joint result for all 21 runs is (87±14 [ stat .]±7 [ syst .]) SNU (1 σ ). The present neutrino recording period GALLEX II is continuing with one solar exposure every four weeks.

International audience; We have measured the rate of production of $^{71}$Ge from $^{71}$Ga by solar neutrinos. The target consists of 30.3 t of gallium in the form of 8.13 M aqueous gallium chloride solution (101 t), shielded by $\approx$ 3300 m water equivalent of standard rock in the Gran Sasso Underground Laboratory (Italy). In nearly one year of operation, 14 measurements of the production rate of $^{71}$Ge were carried out to give, after corrections for side reactions and other backgrounds, an average value of 83$\pm$19 (stat.)$\pm$8 (syst.) SNU (l$\sigma$) due to solar neutrinos. This conclusion constitutes the first observation of solar pp neutrinos. Our result is consistent with the presence of the full pp neutrino flux expected according to the "standard solar model" together with a reduced flux of $^8$B+$^7$Be neutrinos as observed in the Homestake and Kamiokande experiments. Astrophysical reasons remain as a possible explanation of the solar neutrino problem. On the other hand, if the result is to be interpreted in terms of the MSW effect, it would fix neutrino masses and mixing angles within a very restricted range.

The GALLEX collaboration is performing an experiment for the detection of neutrinos coming principally from the p-p fusion reaction in the Sun, via the reaction ve +71Ga →71Ge + e-. The experiment is running in the Gran Sasso Underground Laboratory of INFN, using as a target 30.3 tons of gallium in the form of 8.13 molar aqueous GaCl3 solution. A report is given of the status of GALLEX after the end of the operations devoted to the removal from the solution of the cosmogenically formed Ge isotopes, completed in the middle of 1991. The experiment is now collecting data on solar neutrinos and the data analysis is in progress. Preliminary results concerning the first year of measurement are presented.

The GALLEX result 83 ± 19 (stat.) ± 8 (syst.) SNU is two standard deviations below the predictions of stellar model calculations (124–132 SNU). To fit this result together with those of the chlorine and Kamiokande experiments requires severe stretching of solar models but does not rule out such a procedure, leaving the possibility of massless neutrinos. It clearly implies that the pp neutrinos have been detected. The Mikheyev-Smirnov-Wolfenstein (MSW) mechanism provides a good fit, and the GALLEX result fixes the Δm 2 and sin 2 2 θ parameters in two very confined ranges (around Δm 2 = 6 × 10 −6 eV 2 and sin 2 2 θ = 7 × 10 −3 and around Δm 2 = 8 × 10 −6 eV 2 and sin 2 2 θ = 0.6). Explanations of the solar neutrino problems based on the decay or magnetic interactions of neutrinos are disfavoured.

The new and the old. It is unpleasant for scientists to hear in a speech results which have been known for years and have already been mentioned in 10 different lectures.

The Stanford group1 has recently detected solar global oscillations in the range 160–370 min and interpreted them as internal gravity modes of degree l = 1 and l = 2. Other observations2,3 also indicate the existence of low-degree solar gravity modes. Whereas the high-degree 5-min oscillations are sensitive to the properties of the convective zone essentially, the low-frequency modes (gravity modes) are sensitive to the physical conditions in the solar core. Other constraints on the solar core are given by the observed value of the neutrino flux, which is lower than the flux predicted by the standard models, and by the splitting of the low-degree 5-min oscillations. As far as the neutrino flux is concerned, a possibility to reduce it has been explored by Schatzman and Maeder4 by introducing a turbulent diffusion mixing. In this paper we study the influence of such mixing on the periods of low-degree l gravity modes, which do not present the difficulties of the high-degree gravity modes5. We find that these periods depend strongly on the pseudo-Reynolds number4, and we derive the range of this parameter compatible with the recent observational results.

Stellar rotation generates instabilities1 which have not been taken into account in classical computations of stellar evolution. In particular, these instabilities may produce turbulent diffusion with important consequences over long time scales. Thus it has been shown2,3 that the loss of angular momentum which occurs in the external stellar layers due to stellar wind and magnetic braking4 leads to a redistribution of angular momentum. We show here that there are observational and theoretical reasons to suspect that a slow diffusion process due to a mild turbulence is operating in stellar interiors. Turbulent diffusion may have important consequences for the solar neutrinos problem and the (3He/4He) ratio at the solar surface.

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.

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.

The field is supposed to be independent of z but is periodic in x and y. m and n being integers, the field has neutral lines along the z axis for the coordinates: kx = (m + 1/2) pi and ly = (n + 1/2) pi , k and l being the wave numbers of the periodic structure. The force-free field considered here has been derived for further application to the theory of sunspots and solar flares. Consideration is given for the stability problem using a uniform gas in which the z free field is imbedded. The contribution to stability of an arbitrary perturbation in the neighborhood of the neutral lines is discussed. Compared to the case of cusped geometries, the fluid is not confined by the magnetic lines of force and, consequently, has no reason for being stabilized by the curvature of the lines of force. (B.O.G.)

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.

other effects of the magnetic field, although we know quite well that in the plage areas, and probably in the chromosphere, this is a very crude assump­ tion. We shall also disreg ard the dynam ics of convective zones, because for the Sun this is not properly an atmospheric problem. As far as the Sun is con­ cerned, we shall restrict our discussion to a rather thin layer, the high photo­ sphere and the low chromosphere. The relevance of such a restricted study to astrophysics is twofold: first, the dynamics of atmo sphe res free from mag­ netic fields presents such a varie ty of physical problems, some of which have not been studied, that it is wort h while to discuss the work that has been done in the field and to situ ate the yet-t o-be-discove red areas with respect to the

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.

Some ideas are developed concerning solar flares which have been presented earlier by the author (Schatzman, 1966a). Emphasis is laid on the problem of energy transport; from the energy supply to the region of the optical flare, on the storage of low energy cosmic ray particles in a magnetic bottle before the beginning of the optical flare, and the mechanism which triggers both the optical flare, and the production of high-energy cosmic rays. The relation between solar and stellar flares is considered.

It is possible to predict the amount of gamma rays which are produced in various astronomical objects = gamma rays due to nuclear reactions, to bremsstrahlung, to cosmic rays, to annihilation of matter and anti-matter. These predictions are compared to the results of the observations with Explorer XI and are used to suggest new experiments. The following experiments are suggested: (1) to measure the γ flash associated with Supernovae; (2) to study the energy spectrum of γ rays from radio-sources; (3) to study the γ rays produced in the galaxy, in the halo, and in extragalactic nebulae.

The nuclear physics of the spallation reactions leading to the formation of lithium, beryllium, and boron from proton bombardment on light nuclei is reviewed. A large amount of experimental data is gathered, including in particular several measurements made at Orsay with the 150-MeV synchrocyclotron. A simple rule is devised which classifies quite neatly the cross sections in term of their isotopic spin parameters. This rule can be used to predict the results of unmeasured reactions. For 12C and 16O target nuclei, more accurate determinations are made with the help of calculations based on statistical models. All this information is used to determine the formation ratios of the Li, Be, and B isotopes in CNONe, first by protons of fixed energies, second by cosmic ray protons with an extended energy spectrum. We do not know of course the exact shape of the spectrum giving rise to these Li Be B, but we may assume that they are of the type commonly found in cosmic ray physics: exponential in rigidity or power of kinetic energy. Fortunately, the isotopic ratios thereby obtained are largely insensitive to the shape of the spectrum. Different ratios could of course be obtained from certain special types of spectra (for instance from much steeper spectra). This possibility is only briefly discussed here; it will be more fully discussed in a companion paper. The nuclear reactions possibly responsible for the alteration of the ratios after their formation are discussed next. Finally, the observations of these elements in natural settings are summarized, compared and discussed in terms of the formation and destruction rates, and some conclusions are drawn. The astronomical information gathered so far is consistent with the following picture: each star generates its own Li, Be, B, by proton irradiation of the stellar atmosphere. The isotopes 6Li and 7Li are later partly depleted by proton capture reactions, presumably at the bottom of the convective zone. One of the main results of this paper is that, within the uncertainty of the evaluation, the meteoritic 11B to 10B ratio is equal to its formation ratio on CNONe. This result therefore leads, for the formation of the light elements in the solar system, to a model somewhat different from the FGH one. The 7Li to 6Li formation ratio has a value smaller than the meteoritic one, but the alteration can be ascribed to (p, α) reactions at temperatures between 2 and 4 million degrees at the bottom of the surface convective zone of the young sun, and this process would not alter the 11B10B ratio. A tentative picture of the history of the solar system would go as follows: from energetic considerations, we are led to think that the Li Be B have been formed even before the Hayashi (fully convective) phase of the sun. The 7Li6Li ratio would then have been altered during the Hayashi phase. This material would still later have been separated from the sun. An alternative picture is also sketched, based on the assumption of a special type of proton spectrum, of the kind mentioned above.