Many of the important events in the life of a star occur, or are thought to occur, during the red giant or supergiant phase of evolution. For example, in heavy and intermediate mass stars supernova explosions terminate normal evolutionary processes while in lower mass stars the stellar envelope is entirely removed giving rise to planetary nebulae and, subsequently, white dwarfs. Theoretical calculations suggest that before the onset of these rather drastic events, a significant amount of nucleosynthesis occurs, giving rise to enhanced surface abundances of He, C, N and s-process elements (e.g., Iben and Truran 1978; Renzini and Voli 1981); loss of the envelope material by stellar winds, planetary nebula ejection and supernova explosions produce overall galactic enrichment in these elements.

Although transient decreases in cosmic ray intensity of the type first reported by Forbush (1937) have been observed and studied for more than 40 years using a variety of detectors at many locations, from medium depths underground to those on spacecraft far from Earth, the precise nature of the physical process causing these events is not yet clear (see, for example, McKibben 1981).

The realization that the nuclei of planetary nebulae are stars which evolve with a time-scale of ~ 104 yr (O’Dell,Seaton) has prompted several theoretical investigations of the late stages of stellar evolution (Vila, Divine, L’Ecuyer). Vila has assumed that all nuclear burnings have ceased in these stars, and that the energy release is entirely gravitational. He showed that the inclusion of neutrino energy-loss processes based on the universal Fermi interaction of Feynman and Gell-Mann reduced the theoretical evolution time by two orders of magnitude to a value comparable with the observed time. His theoretical models, however, have effective temperatures greater than those observed by a factor of six.

The radio source, Cen A, is large and complex with many peaks in the brightness distribution over an area about 4 x 10 degrees. The peculiar elliptical galaxy NGC 5128 lies between the two strong inner radio brightness peaks and is centred on a weaker central radio source. This radio source is in the centre of the dust lane which divides the galaxy and may be related to the infrared, X-ray and γ-ray sources.

Baseline ripple measurements are of two general kinds, those associated with on-source mechanisms and those with off-source mechanisms (Poulton 1974; Morris 1974). We are here principally concerned with on-source baseline ripples, which occur when a strong continuum radio source is present in the beam. The ripples are particularly conspicuous (Padman 1977, 1978) with a large instrument, such as the Parkes 64-m telescope, where the ripple period is rapid. Here baseline uncertainty becomes especially severe for the detection and study of wide lines, such as the H/He complex and the formamide multiplet near 1.54 GHz. Off-source baseline ripples also occur because of other effects, but in principle they can be removed by subtracting a reference-region spectrum taken while tracking the telescope over the same hour-angle range at the same declination under stable conditions. Improvement of the off-source baseline ripple which arises from stray radiation would also be expected to result from the technique described here.

The Chatterton Astronomy Department of the University of Sydney is proposing the construction of a very high angular resolution stellar interferometer of major astronomical and international significance. Based on the prototype modern Michelson stellar interferometer which the Department has developed, the new instrument will be used in a wide range of astrophysical programmes. The siting, specification, design and costing of the instrument are outlined.

We report on the identifications of 15 new X-ray selected Active Galactic Nuclei (AGN). The AGN have been discovered during an ongoing program to identify and study the optical counterparts of X-ray sources detected by the HEAO-1 satellite. The new AGN add to our existing data base of 26 making a sample of 41 objects which are the subject of a multiwavelength study including radio, infrared, optical, UV and X-ray observations. As part of this study 8.4 GHz flux measurements have been made at Parkes. Radio-optical-X-ray continuum spectral index comparisons are presented.

I look briefly at protostellar environments and at what information can be gained from the millimetre waveband. A short overview of the theory of protostellar environments and evidence of disks will be followed by a more detailed review of recent publications of observations of protostellar halos/disks, specifically in 3 mm.

This paper examines the importance of astronomy education for a rural society in a third world country. Some conclusions are drawn about methods of introducing astronomy to school students and, through them, the entire village. The conclusions are based on the author’s direct experience in addressing high school students in several rural towns in India.

Between the time when the shock approaches the outside of the progenitor star, when the shocked material is highly ionized, and a few months later, when the material has cooled and recombination is almost complete, details of the coupling of radiation and the hydrodynamics of the shock propagation may be significant, with a subsequent effect on the photosphere and thus spectra. I argue for the inadequacy of current analyses of shock breakout and of the customary adoption of self-similar expansion of an initial structure for spectral synthesis of the first few months, in place of a complete hydrodynamic simulation. Progress towards a full radiative hydrodynamic simulation including relativistic effects and detailed line opacities is discussed.

The conditions for the equality of the line source functions associated with fine structure transitions in a multilevel atom have been examined by several authors. The equality or otherwise of the source functions depends largely on the value of the fine structure collision rate, equality occurring when this rate becomes infinitely large. The fact that the theoretical collision rates between fine structure levels of alkali atoms are so large suggests the possibility of simplifying complicated multilevel atom transfer problems by the consideration of the limit of an infinite fine structure collision rate.

The discoveries made by the Voyager 2 spacecraft at Uranus in January 1986 are discussed in the light of the modern Laplacian theory for the formation of the solar system. Various accounts of this theory, which has as its basis the concept of supersonic convective turbulence, have been presented at previous meetings of the ASA (Prentice 1977, 1979, 1981a). The most important confirmation by Voyager was the discovery of 2 new satellite groups near orbital radii 2½ RU and 3½ RU (RU = Uranus’ equatorial radius = 26, 200 km), as first predicted in 1977. The discovery that the densities of the Uranian satellites are consistent with these bodies having condensed in a single compositional class, consisting of anhydrous rock, NH3 ice and CH4.6H2O clathrate hydrate in normal solar proportions, confirms the hypothesis that the chemistry of all planetary/regular satellite systems are accounted for by a single choice of the turbulence parameter, namely β = 0.107 ±0.001. The implication of the Voyager data for the origin of comets is also discussed.

Solar type III radio bursts often occur for prolonged periods (≳ 1 hour) with small time intervals (≲ 1 minute) between bursts. Such phenomena usually are confined to decametre wavelengths (frequency ≲ 100 MHz) and are called ‘type III storms’ (e.g. Stewart and Labrum 1972).

This paper discusses the techniques of presenting data both verbally, with emphasis on the use of viewgraphs, and as posters. The views expressed summarise a discussion which involved about 40 young astronomers: they are of particular relevance to those amongst us of the generation which has had these media thrust upon it without training.

Semiconvection is the name given to a situation that arises in the evolution of large-mass main-sequence stars and lower-mass horizontal-branch stars, in which a layer forms where almost all of the heat flux is transported by radiation, but where slow convection is required to redistribute a stably stratified solute (e.g. helium). For a general discussion on semiconvection, see Spiegel (1969). The main problem is to determine the correct relationship between the solute distribution and the temperature gradient in the inhomogeneous layer. Ledoux (1947) and Schwarzschild and Harm (1958) have proposed two very different prescriptions. Since theory and experiment indicate that the Schwarzschild-Harm (SH) prescription is correct for the onset of convection (in the form of overstability), Spiegel (1969) has proposed that SH are correct. However, neither observation (oceanographic or laboratory) nor theory precludes a substantial deviation from the SH prescription as applied to finite amplitude semiconvection. The observational evidence is only readily applicable to stars if Pr≳, 1, where Pr is the Prandtl number of the fluid. In fact, Pr≪ 1 in stars. It is shown below that if one could have stars in which Pr ≳ 1, then the SH prescription would probably be wrong, and the Ledoux criterion might then be nearer to being correct. In the real situation (Pr≪ 1), observations or experiments are lacking and theory alone does not provide an unequivocal answer to the problem. This paper does not attempt a complete discussion of the problem, and a more detailed report will be submitted elsewhere. Some aspects of the problem have already been discussed in the context of the giant planets (Stevenson and Salpeter 1977).

The passage of the planet Venus across the face of the Sun is an astronomical spectacle which no living person is likely to have seen. The phenomenon has played an important role in the history of astronomy and in stimulating world science and geographical discovery during the 18th century. But to Australia the transit of 1769 is of truly momentous significance: during the course of an expedition to the South Seas specially organized to observe it, Lt. James Cook discovered and chartered the east coast of Australia, hoisted the English flag, and took possession in the name of King George III.

In a current programme at the Molonglo Radio Observatory using the high-resolution pencil beam of the instrument (∼3′ arc) an attempt is being made to extend the measured spectra of known planetary nebulae down to 408 MHz. Of 23 such planetaries already investigated, 14 have been detected. The main results will be given elsewhere; here it is proposed to discuss in detail only the well-known planetary nebula IC 418.

The very low background observed from Antarctica in a window from about 2·25 to 2·45 μm can be exploited as a way of making deep near-IR surveys over wide areas of sky. Imaging surveys using the entire window can cover large areas of sky to limits of around K = 20, and can be used to study galaxy evolution and to search for high-redshift quasars, dust-obscured quasars and brown dwarfs. It is also possible to make spectroscopic surveys in this window. The window includes molecular hydrogen emission and CO absorption in galactic sources, and can also be used to search for emission lines such as Hα in high-redshift star-forming galaxies.

In a previous paper of this issue (Stewart and Nelson 1979 — Paper A) we showed that for extended bursts a good correlation exists between the observed 100 keV X-ray slux density and the 3.75 or 9.4 GHz microwave flux density. We also showed that the microwave spectrum of these bursts was much flatter (S ∝ f 1.0 on the average) than the optically thick (self-absorbed) spectrum observed for impulsive microwave bursts (Crannell et al. 1978; Dulk et al. 1978). Furthermore, the microwave turnover frequency was > 10 GHz in eight of the nine events studied and <20 GHz in four of these cases. The remaining event, which was severely occulted by the solar limb, had a turnover frequency of ∽ 1 GHz.