Radio, optical and X-ray observations of a complete flux-limited sample of southern bright radio sources have been analysed to investigate beaming and orientation effects in the different wavebands. We conclude that, in addition to beamed optical and radio components, there is evidence for anisotropic X-ray emission.

A common test for hydrodynamic calculations is the Boss and Bodenheimer (1979, 1981, hereafter BB) problem in which an isothermal, spherical cloud of 1 M⊙ is given a cos (2Φ) density perturbation and the ensuing evolution studied.

The first QSO with a redshift z > 4 was found using a combination of UK Schmidt Telescope (UKST) plates and the APM automatic plate measuring machine (Warren et al. 1987a). By continuing to make use of UKST survey plates plus the APM facility we have added substantially to the number of known QSOs with z > 4. A brief description of the general survey technique is presented together with a preliminary discussion of some of the results obtained so far.

Ten years ago I put forward the suggestion that the Sun may possess a small burnt-out helium-rich core covering some 2-3% of its mass (Prentice 1973a,b). The purpose of this chemically inhomogeneous solar model was to account for the anomalously low flux of neutrinos being emitted by the Sun, as observed by Davis et al. (1971).

The visual spectra of some hot stars, including P Cygni, have emission with associated absorption troughs ˜ 102 km s-1 on the short-wavelength side (Beals 1929, 1951). These P Cygni profiles are easily understood in terms of mass flowing away from the star. Later, rocket observations of the far-ultraviolet resonance lines (Morton 1967) showed that the phenomenon is rather common among hot stars and the velocity shifts could be from 1000 to 3000 km s-1, demonstrating that the mass must be escaping from the star. Resonance lines provide the strongest absorption in the shell where neither the density nor the radiation field is high enough to leave many ions in excited states. Since the ion stages likely to be present around a hot star have their resonance lines shortward of the atmospheric cutoff, space observations are essential in this investigation. Figure 1 shows the P Cygni profile of O VI in ς Pup obtained with Copernicus satellite spectrometer.

The Molonglo Observatory Synthesis Telescope (MOST), operating at a frequency of 843 MHz, is currently surveying the southern galactic plane between 245° <l<360° and −1.5°<b<1.5°. The resolution of the survey is 43″ (HPBW), providing radio continuum maps of unprecedented resolution and sensitivity (1 mJy/beam) in this part of the sky. The survey involves 12-hour synthesis observations of over four hundred fields, each extending over one degree. Eighty of these have been mapped in the past year, bringing the number now completed to three hundred. The survey is revealing many faint structures with intriguing morphology, including filamentary emission associated with the Vela supernova remnant, and a number of very weak (<5 mJy/beam) disc-like objects.

The proposal made to ASTEC for an Australian systhesis telescope (AST) is for a high-sensitivity, high-resolution synthesis array to be located at the Australian National Radio Astronomy Observatory, Parkes, and used in conjunction with the existing 64-m antenna at that site as a national facility (Wellington 1976). During the past 18 months a design study group consisting of representatives from the Australian National University, University of Sydney, University of Tasmania and CSIRO has been investigating the design of such an array. This paper reports on one aspect of this design, the array configuration.

A simple model is presented for electron acceleration in extragalactic radio sources with two hot spots. The effect of diffusive shock acceleration by multiple shocks is calculated numerically, with adiabatic and synchrotron losses included. It is found for the sources 3C 20 and 3C 268·4 that a consistent set of model parameters exists which reproduce the observations. The model fails to reproduce the observations for the source 3C 196.

The probability of a collision with each of the terrestrial planets due to each of the Aten-Apollo-Amor asteroids discovered through to 1989 May is calculated; the range of possible impact velocities is also given in each case. For Mercury there are eight possible impactors known, with a mean collision probability of 1.30 × 10−9 per year; for Venus, the 32 planet-crossing asteroids give a mean collision probability of 9.63 × l0−9 per year; for the Earth the corresponding figures are 65 and 6.93 × 10−9 per year; and for Mars, 116 and 3.41 × 10−10 per year. The rate for Mars does not include the full range of Mars-crossers (i.e. those of 1.30<perihelion distance <1.67 AU are not included here), and for the interior planets any undiscovered population of asteroids would also alter the mean probability of an impact.

Some statistics from 368 plates of 111 double stars observed between July 1965 and January 1969 with the Yale-Columbia 26-inch refractor at Mount Stromlo Observatory, are presented. The results of plate measurements, and a description of the work, are to be published elsewhere.

The origin of cylindrically symmetric supernova remnants (SNR) is discussed. The results of numerical simulations of the two best examples of barrel-like SNRs, SN 1006 and G296.5+10.0, are presented.

A considerable amount of observational interest in short timescale phenomena has developed in optical astronomy in recent years. This interest has stemmed primarily from search efforts directed towards optical pulsars and the study of rapid fluctuations in cataclysmic variable and flare stars. Such studies have been made feasible by the development of the necessary photon pulse-counting technology required for rapid data sampling.

The arrangement whereby the front end of a radio astronomical receiver is located at the focal plane of a paraboloidal telescope causes the incoming waves to be reflected between focal plane and vertex. The result is a sometimes simple, sometimes complex wave pattern on the output of an associated spectrometer and is known as baseline ripple.

Sources of the Type I storms are thought to lie on closed magnetic loop systems above bipolar sunspots. Usually one sunspot is stronger than the other in the bipolar magnetic structure, and accordingly only one radio source associated with the stronger sunspot is usually observed. Occasionally however a double radio source is observed in conjunction with the bipolar sunspots. In such a case the double radio source should be intrinsically bipolar, viz. the two components should emit opposite senses of circular polarization (in this paper we use the word polarity for simplicity).

This is a preliminary report on the first Strömgren–Hβ photometric survey of yellow supergiants in the Magellanic Clouds. Less luminous supergiants have been chosen in preference for this program in order to facilitate calculation of their physical parameters. This will not only provide a basis for future detailed spectral analysis of these stars, but will allow a better calibration of the colours derived from model atmospheres for this type of star. The colours of these stars are more affected by changes in metallicity than the hotter stars more frequently studied, and since they are also young, they reflect the metallicity of their local InterStellar Medium (ISM). If indeed the Strömgren abundance index m 1 can be calibrated successfully for these stars, then their observation in any galaxy will provide the metallicity of that particular ISM. Our results show that it is important for future colours to be calculated over the range of turbulent velocities important for supergiants.