Japanese activities related to radio astronomy in Antarctica are briefly reviewed.

The Japanese base, Showa, is located on the coast and is based on rocks rather than ice. A 10 metre diameter microwave antenna has been built at the Showa station and a series of VLBI experiments have been made between the Showa base and a station in Japan in 1988–1989. The experiments have been geophysically motivated and an accurate measurement of the location of the Showa base was determined relative to Japan, which has a well determined position relative to other continents.

The station Vostok is on the polar cap at an altitude of about 3500 m. Vostok comprises a special complex for geophysical research together with accommodation and power generating facilities. Its location far inland at a high altitude provides a unique astroclimate. From 1958 to 1980, the mean annual temperatures were -55.3°C at Vostok, -49.3°C at Amundsen-Scott (S. Pole), and -11.3°C at Mirny (near the coast). Mirny recorded an average of 199 days/year with strong wind, Vostok only 3.2. The mean number of days/month with heavy cloud were 3.4 at Vostok, 4.0 at Amundsen-Scott, and 6.6 at Mirny. The number of days/year with little cloud: Vostok : 361, Mirny : 174.

An Indian expedition to Antarctica (to the coastal base Maitri) in the 1989/90 summer made observations of the Sun to study the evolution and decay of supergranules, an experiment which benefited greatly from uninterrupted sessions of a few days. The instrument comprised a heliostat, a 1.2 Å bandwidth blue filter, and a 10 cm aperture lens of about 3 metre focal length with recording on film. During January and February, one continuous period of more than 100 hours completely clear sky occurred, during which the transparency of the atmosphere was excellent. However, at times the seeing was a little poor. More than 2500 photographs were made at 10 minute intervals, as well as some at shorter intervals for studying the evolution of other solar features such as flares.

The Center for Astrophysical Research in Antarctica is a new National Science Foundation Science and Technology Center formed to explore and exploit the unique advantages of the Antarctic Plateau for astrophysical observations.

French astronomers have been involved in research programs in Antarctica since 1979 when a successful campaign on helioseismology was done by a collaboration between the Nice University and the Bartol foundation. Several campaigns followed on this subject. In 1984 sub-mm observations of the diffuse galactic emission were done by a collaboration between the LPSP (Verrières le Buisson) and the Bartol foundation. These showed the high quality of the site for such observations not only because of the low water vapour content, which gives good transparency, but also because of the very low sky noise.

The characteristics which make Antarctica interesting for astrophysical research are: i) atmospheric transparency, ii) remoteness iii) geographical and geomagnetic position. Because of previous experience of observation from arctic sites in northern Europe and from isolated mountain sites, groups of Italian astrophysicists were immediately ready to go to Antarctica and bring their equipment to places not easily accessible, in a difficult environment when, about ten years, ago, the antarctic regions became more accessible.

The South Pole air shower experiment (SPASE), a joint Bartol Research Institute and Leeds University project, has been operational since the austral summer of 1987/88. It is a cosmic ray telescope searching for cosmic gamma rays at energies up to 1000 TeV. Although it has a relatively small area (6800 m2), it is situated at an altitude of 2800 m and has a 24 hour coverage, making it very competitive. The angular resolution of 0.°8 at 200 TeV is state-of-the-art in gamma ray astronomy. The astronomical programme includes searches for gamma ray sources, searches for anisotropy in the cosmic ray sky and measuring the energy spectrum over the range 1014-1016 eV.

Many people, including Wernher von Braun, have drawn an analogy between the manned exploration of the solar system and scientific stations in Antarctica. Some of the Space/Antarctic parallels are quite obvious, such as the necessity to select small groups of highly trained individuals who can work together in isolation for extended periods, or in the case of the Moon/Antarctic comparison, the long day/night cycle. However, the parallel can be carried considerably further to include the types of science to be done, and, in some cases, there is even a strong similarity in environmental conditions. It may be worth while to build a new Antarctic station just to learn more about how to do planetary exploration.

These largely historical remarks were meant for those in the audience that had not followed the developments in recent years.

One of the great achievements of astrophysics in this century was the discovery of the source of the solar (and stellar) energy: the fusion of hydrogen into helium. It became also clear that once the conditions for hydrogen burning become unfavourable the star switches to the burning of helium: a contraction of the central region increases the temperature and pressure until the helium starts to burn into carbon and oxygen. In this way one imagines that stars during their lifetime go through successive phases of atomic fusion, with the endproduct of the previous phase as the fusion element for the one following. This succession can continue until the iron core is reached; thereafter the fusion becomes exothermic, and is no longer a viable source of energy; perhaps a supernova should follow here. As we know now (and will be discussed here), this succession is interrupted by mass loss; most stars do not develop beyond the second core, one of carbon and oxygen.

The far IR colors of circumstellar shells are delimited by those with masers; few other objects share the same colors. The resulting (25–12)µm color range is primarily due to secular increases in the mass-loss rate, up to a progenitor-mass dependent maximum. Only the most massive progenitors can sustain the mass-loss rate required by the reddest shells.

1. (1) Mira variables define the tip of the AGB for low mass stars (cf. Feast and Whitelock 1987 fig. 1).

2. (2) The kinematics of Mira variables are a function of period (e.g. Feast 1989 and earlier references) and for Miras in globular clusters the period is a function of metallicity (e.g. Feast 1981). Hence the Mira period sequence is not an evolutionary sequence but represents the sequence of AGB tips for stars of different initial mass and/or chemical composition and/or age.

3. (3) Mira are surrounded by circumstellar dust shells. The mass loss rates are a function of period and light amplitude (Whitelock et al. 1987, Whitelock et al. 1991, Whitelock 1990). The results suggest evolution with increasing pulsation amplitude and mass loss but little change in log P ((2) and (3) do not preclude some (small) change in log P during evolution nor possible phases of decreasing light amplitude and mass loss).

Computations of AGB stellar evolution which include the effects of mass loss are still relatively rare. However, in order to relate numbers of Mira variables, OH/IR stars and carbon stars to associated stellar populations, it is necessary to understand evolutionary timescales on the AGB.

The dominant factors controlling very late AGB evolution are shell flashes and mass loss, and some quantitative estimate of the latter is needed for stellar evolution calculations. The favoured mechanism for the production of the large mass loss rates observed in late AGB stars such as OH/IR stars and dust-enshrouded carbon stars, which have mass loss rates up to a few times 10−5 M⊙ yr−1 (see van der Veen and Rugers 1989 for a compilation), is a dual process involving the lévitation of matter above the photosphere by large-amplitude radial pulsation followed by the formation of grains on which radiation pressure acts to drive the circumstellar material away from the star (Castor 1981; Holzer and MacGregor 1985; Hearn 1990). The studies by Wood (1979) and Bowen (1988) show that, by themselves, neither pulsation nor radiation pressure acting on grains can produce the very large mass loss rates from AGB stars.

Asymptotic giant branch star models are reviewed in relation to luminosity observations and chemical abundance observations of these stars.

The evidence of an exponential distribution of neutron exposures for reproducing the solar-system s-isotopes between Zr and Pb, the main component, comes from a phenomenological analysis of the s-path in the σN versus A plot (see Käppeler, Beer and Wisshak, 1989). The resulting mean neutron exposure is τ0 = 0.30 ± 0.01 mb−1. The study of branchings with no or weak temperature dependence (95Zr; 147Nd, 147,148Pm; 185W, 186Re) allows one to derive an effective neutron density nn =(3.4±1.0)×108cm−3. On the other hand, an effective temperature is obtained from the branchings 134’135Cs, 151Sm, 154Eu and 176Lu: T8 = 3.4 ± 0.5 (Käppeler et al., 1990). Although the phenomenological approach is very useful because it is independent of stellar models, nonetheless it can only lead to effective physical conditions, symplifying the complexity of the astrophysical sites.

Some recent results on planetary nebulae research are discussed.

The idea that planetary nebulae (PN) originate from the outer atmospheres of red giant was first proposed by Shkloskii (1956). In the early 1970’s, it was generally believed that PN were created by a sudden envelope ejection; however, the exact nature of the instability responsible for the ejection was not understood. Furthermore, it was not clear how the observed masses of PN are related to the amount of mass ejected, and there was no explanation of how the observed shell morphologies of PN could be created by such instabilities. From the observed sizes and expansion velocities of PN, we know that the dynamical lifetime of a PN is ~104yr. During this period, the star has to evolve from the red side of the H-R diagram, where the envelope is ejected, to the blue side of the H-R diagram, where the stellar temperature is high enough to photoionize the ejecta. If the star evolves too slowly, the nebula will have dispersed into the interstellar medium before it is ionized. If the star evolves too fast, then the nebula will only be illuminated for a short time before the stellar luminosity drops on the white dwarf cooling track (Renzini 1982). It is therefore surprising that PN is such a common phenomenon, with ~30000 PN estimated to be in the Galaxy now.

A short review is presented on the various methods to construct the HR diagram for central stars of planetary nebulae (CPN).

Over the last several years, evidence has been unfolding that the surface abundances of white dwarfs may evolve as the stars cool. It is possible that some post-AGB stars enter the white dwarf sequence with far less hydrogen and helium than predicted by standard theory of the quenching of shell sources, and with atmospheres dominated by C and O. The interplay of diffusion and episodes of convective mixing may lead first to He-rich atmospheres, then H-rich, and finally He-rich again.

It is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of helium burning, mostly carbon and oxygen. The exact proportions of C and 0 are unknown because of uncertainties in the nuclear rates of helium burning.

The one great point of similarity between the coronae of hot and cool stars is that both are spatially extended regions of more-or-less tenuous gas that is flowing outward, and at least some of which is at a temperature in excess of 106 K. Coronae defined in this way are almost universal among stars—excepting cool supergiants—but this similarity may hide significant differences in the processes that produce coronae. There are two rather different paradigms for their origin: the cool-star paradigm and the hot star paradigm.

The coronae of cool stars like the sun are of such a low density that radiative cooling is inefficient; the outward flow is weak enough that there is a fairly extended subsonic flow region. The outer corona is heated by a flux of wave energy, and some of this energy is then conducted inward to heat the inner corona. The outflow is driven by the pressure of the heated gas, assisted perhaps by wave pressure. The structure of the corona is greatly affected by the topology of the magnetic field, which channels the outflow and governs the transport of energy and momentum by waves.