Hypervelocity impacts are considered to be the main mechanism for the production of craters on the surfaces of planets and moons. Two- and three-dimensional numerical simulations for the first few seconds of large-body impacts will be discussed. Both normal and oblique impacts will be considered, with particular emphasis being placed on the distribution of impact products.

Ground level detectors observed several major changes in the primary cosmic-ray flux during November 4960. Large increases, of solar origin, occurred on November 12 and 15, and a smaller one on November 20. The galactic flux in the region of the Earth was severely reduced by a Forbush decrease on November 12, and remained notably depressed until November 25. Considerable magnetic activity was observed throughout the period. Several models have been proposed to account for these observations.

An attempt has been made to examine the nature of 3-minute umbral oscillations in order to identify their origin. For this purpose we have calculated, on the basis of Musielak and Rosner (1987), the fast-mode energy spectra generated in a typical sunspot convection zone (Yun 1968). The computed energy spectrum is fed into the lower boundary of the sub-photospheric resonant cavity to examine the characteristics of the wave propagation through the SS umbral atmosphere (Avrett 1981). The upward velocity spectra computed at various heights are presented and their behaviour compared with observations.

The term white dwarf was originally introduced, some 50 years ago, to describe intrinsically faint A-type stars. Spectroscopic studies and theoretical considerations confirm the suggestion that these are degenerate objects. Photographic colorimetry of faint proper motion stars can readily distinguish the blue objects and in this way several hundred white dwarf candidates have been discovered, mainly by Luyten. Accurate photometry of about 1000 of these stars has led to accurate estimates for the space density of 1.5 = 10−3 pc−3. However, subluminous late-type stars are more difficult to detect among the multitude of main sequence stars and some additional criteria are needed.

The most prominent features in the spectra of Sgr A and Sgr B2 between 1636 and 1640 MHz are absorption lines corresponding to the 2π3/2, J = 3/2 ground state transitions of the isotropic species 18OH, which have rest frequencies of 1637.5 and 1639.4 MHz (Rogers and Barrett 1966). As a result of Doppler shifting, the lines of each transition are spread over a frequency range greater than 1.5 MHz. There are also present emission features which Zuckerman et al. (1971) have identified with the 110 -l11 transition of formic acid (HCOOH), which has a rest frequency of 1638.805 MHz. In view of some disagreement in the literature over the 16OH/18OH abundance ratio (Wilson and Barrett 1970; McGee et al. 1970), and of the baseline uncertainties in the spectra published in support of the HCOOH detection, we have obtained spectra of the two sources over the frequency range under discussion.

Any theory dealing with type IV solar radio bursts must explain the observed evolution of their brightness temperature and polarization. The behaviour of isolated, moving type IV sources is characterized by a long period of constant and low polarization during the major part of their lifetime, followed by a substantial increase in the degree of circular polarization during the declining phase. This behaviour puts severe constraints on and gives valuable clues as to the evolution of the physical conditions within the source.

The LYMAN project has been the subject of industrial Phase A studies in both Australia, and within ESA. These studies have demonstrated an extremely useful international collaboration, as well as a very successful collaboration between University and Industry. Working together, we have identified all critical problems of feasibility, and have developed at least one, usually more than one, method of overcoming these while remaining within the cost and complexity envelope of the overall mission.

The LYMAN mission will be the subject of a competitive selection process within ESA at the end of November 1988. One of five projects will be selected to go forward into later phases. However, the Australian LSWG are confident that, with the enormous support that the LYMAN project commands on both sides of the Atlantic, with the tremendous scientific merit of the proposed mission, and with the demonstration of feasibility of the mission in two separate Phase A studies, that LYMAN will be the successful candidate.

Spectropolarimetric observations of SN 1987A obtained with the AAT are presented and discussed. The foreground interstellar polarization is estimated to have a value of 0.8% at position angle 40°. In the early stages polarization features on the absorption troughs of the P-Cygni profiles are observed. At later stages the polarization is dominated by the effects of electron scattering. After correction for the effects of interstellar polarization the position angle of the electron scattering polarization is 110°. The spectrum of the polarized radiation shows broad redshifted features corresponding to the emission lines which can be understood as the consequence of electron scattering in an expanding atmosphere. The position angle observed is consistent with the elongation of the supernova image seen by speckle inteferometry.

Recently a programme of observing 21 cm-λ solar radio bursts with high angular resolution has been commenced at the Fleurs Radio Field Station of the School of Electrical Engineering, University of Sydney. In some preliminary measurements fringes from two 2-element E-W interferometers, spaced at roughly 3800 and 1900 wavelengths, have been recorded simultaneously.

This paper briefly discusses the Aten, Apollo and Amor asteroid types (collectively referred to as AAAs), their perihelion distribution and orthogonal motion. There are 90 objects in these classes: 6 Atens, 46 Amors and 38 Apollos. The maximum distance to the ecliptic plane of each class follows an exponential function.

The possibility is considered that core emission in pulsars results from secondary e± pairs generated through linear acceleration emission (LAE), rather than the conventional curvature emission (CE). It is found that this is possible in principle, but only under conditions that appear not to be satisfied in practice.

The Culgoora-3 list of radio sources (Slee 1977) contains measurements at 160 MHz of about 2000 sources which had earlier been examined at 80 MHz (Slee and Higgins 1973, 1975). The observations were made with the Culgoora radioheliograph, a 3-km-diameter ring of 96 reflectors, which achieves angular resolutions (full half-power width) of 3′.7 and 1′.9 arc at 80 and 160 MHz respectively; it has an effective collecting area of ~6000 m2.

A China-Japan X-ray balloon flight took place in 1988 August. Preliminary results are presented for the energy spectrum of Cyg X-1.

3C75 consists of a pair of twin-jetted radio galaxies near the centre of the cluster Abell 400 which is a strong extended X-ray source. Fibre spectroscopy from the AAT, combined with number counts of the galaxies in Abell 400 give the gravitational potential of the cluster which is used to model the X-ray source. The inferred pressure of the X-ray gas suggests that the lobes of the radio source are probably confined. Evidence of excess X-ray emission near the centre of the cluster is also found.

High resolution studies of clusters of galaxies at radio frequencies may contribute substantially to our knowledge of the properties of radio galaxies, their evolution and their luminosity function. A considerable amount of statistical information is already available on the correspondence of radio sources and clusters; the present investigation is aimed rather at a detailed examination of the sources and their identification with actual galaxies or other objects.

Radio maps of extragalactic radio sources made with the Westerbork, Cambridge and V.L.A. synthesis telescopes have revealed collimated jets extending from the cores to the radio lobes (see Miley 1980 for a review). These observations have provided outstanding support for ‘beam models’ of extragalactic radio sources (Scheuer 1974, Blandford and Rees 1974). Two crucial pieces of information to emerge from high resolution observations are the behaviours of jet full width half maximum (FWHM) and surface brightness with angular distance from the core. Such data have for instance been provided by Formalont et al. (1980) and Bridle et al. (1981) for the jets in 3C-31 and by Willis et al. (1981) and Bridle (1981) for the jets in NGC 315. An important point is that the relationship between jet surface brightness and FWHM is not in general as predicted by simple magnetohydrodynamic models (Bridle 1981).

The variable X-ray source in the direction of the Small Magellanic Cloud (SMC), SMC X-1 (2U 0115-73) was discovered by Leong et al. (1971). X-ray eclipses with a period of 3.8927 ± 0.0010 days were subsequently reported by Schreier et al. (1972). Identification of the X-ray source with SK 160, star number 160 in the list of Sanduleak (1968), was proposed by Webster et al. (1972) on the basis of the similarity of its spectrum with that of the optical counterpart of Cyg X-1.

The third Uhuru catalogue of X-ray sources (Giacconi et al. 1974) contains X-ray source positions given to a much higher precision than was previously available and this fact has given considerable impetus to the search for optical and radio counterparts. Many such identifications have now been made and confirmed, e.g. by discoveries of correlated variability.