we use Monte Carlo simulations of the period distribution of magnetic cataclysmic variables to show that the synchronised AM Herculis-type systems and the asynchronous Intermediate Polars are essentially unrelated systems following different evolutionary scenarios.

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.

This paper evaluates the COSMOS database as a tool for large-scale automated optical identification programs. Firstly, we explore the limitations inherent in the database by a study of regions centred on clusters of galaxies. We then perform an automated search in the database for a sample of previously measured optical objects and compare the properties of corresponding objects. Finally, we describe a set of new plotting routines in AIPS (Astronomical Image Processing System) designed to plot COSMOS-derived ellipses and, optionally, magnitudes onto radio images.

The astrophysical literature contains many discussions on exactly which changes in a star’s structure are responsible for the extremely large radii found after core hydrogen exhaustion. Different authors favour different mechanisms. Unfortunately none of the proposals are easily verified nor are they easily disproven. In this paper we examine the suggestion that it is the increased central mass concentration (i.e., the growth of the hydrogen exhausted core) which is the primary agent responsible for envelope growth.

If the relative velocity between a plasma and a molecular cloud impinging on it exceeds the Alfvén critical ionization velocity, then the surface of the molecular cloud can be ionized. This phenomenon has been used to model some of the ionized regions at the Galactic Centre. A review of the mechanism behind Alfven’s critical ionization phenomenon is presented here, and its use at the Galactic Centre is discussed.

Spectroscopic imaging of the SNR RCW 103 has revealed extensive emission in near-infrared lines of H2and [Fe II], where the blast wave is encountering a molecular cloud. The H2 appears to be located outside the [FeII], a morphology which challenges our understanding of shock wave physics. It is suggested that reverse shocks may be responsible for the phenomenom.

The absorption counterpart of curvature emission is reexamined based on the Landau-Lifshitz approach. Early derivations led to the conclusion that maser emission is not possible, but these early derivations neglected a drift effect which was first discussed by Zheleznyakov and Shaposhnikov. When the drift effect is included, the derivation implies that curvature maser emission is possible. It is shown that for maser emission to be possible, the Lorentz factor needs to satisfy γ ≳ 103 for radius of curvature of the magnetic field lines RB ≈ 106 to 109cm and frequency ω ≈ 107 to 1011 s−1. Possible application to pulsars is discussed.

High resolution imaging at radio frequencies has revealed several long, filamentary, non-thermal sources in the Galactic Centre region. One of these, known as the Snake, is unique in that it lies outside the Galactic Centre Lobe, and has two kinks along its length, one of which appears to be associated with a small, resolved source. For this work the Snake is assumed to be embedded in a region where both the magnetic field and the particle energy spectrum are uniform. The Snake is then modelled as an enhancement over the background of the particle energy spectrum. Some preliminary results from this model are presented here.

The radio emission associated with SN 1987A appears to be synchrotron emission resulting from the acceleration of electrons at the interface between the outward moving shock wave and clumps of circumstellar material. The Australia Telescope Compact Array is now able to resolve this region, which has dimensions of ~ arcsec, revealing a slight (10%) asphericity in the distribution of the low density gas within the [OIII] circumstellar ring. Assuming that the radio emission arises from a region just behind the shock front, we deduce a mean radial expansion velocity, from 1987 to 1992, of 29 200 kms. First observed contact of the shock with the [OIII] circumstellar ring could occur as early as mid-1993, depending on the deceleration in the intervening gas. This will probably be closely followed by shock-excited optical lines, a strong X-ray outburst and a further increase in the radio emission.

The Parkes radio telescope has been used to search a list of small, dense southern dark clouds and Bok globules for ammonia emission at 23.7 GHz. The ammonia observations, together with IRAS data and the cloud’s visual appearance, have been used to determine a short list of dark clouds for observation with the infrared imaging system (IRIS) on the Anglo-Australian Telescope, in an attempt to determine the dust density distribution within the clouds. Near-infrared images of a number of the short listed clouds have been obtained with IRIS at J, H and K’. Preliminary results are reported for this ammonia survey, together with IRIS images of the strong ammonia source DC 297.7–2.8. Coincident with the dense ammonia core of this object is an IRAS ‘core’ source, IRAS 11590–6452 and an extremely interesting near-infrared source, which lies on the edge of the error ellipse of the IRAS source.

When a rotating magnetised system (angular speed Ω), such as a planet or star, loses mass there is necessarily an energy dissipation associated with the mass loss. Consider mass loss at rate M, such that the matter is flung off with the orbital speed ΩR1, at a radius R1 ≫ R0, where R0 is the radius of the planet or star. The power released is approximately equal to the power Prot = 1/2MΩ2R2 carried off in rotational kinetic energy. Part of the energy released is carried off as magnetic energy in the escaping plasma, and the remainder is released through dissipation of currents. Such dissipation plausibly leads to the acceleration of particles. The power released should be important for Jupiter and for some rapidly rotating stars. For most stellar systems, the power released is small compared to that required to drive a wind.

The current ephemerides include an allowance for umbral oblateness based on the flattening of the Earth’s geodetic reference spheroid; there are few published estimates for umbral oblateness derived directly from the geometry of a lunar eclipse. This paper reports umbral oblateness values which have been derived from 7,400 crater contact timing observations of twenty-one lunar eclipses by amateur and professional astronomers since 1972. The observed umbral oblateness was found to be typically three times the geodetic reference spheroid flattening.

There is a need for standardised terminology in the field of astronomy. A project on behalf of the International Astronomical Union has been undertaken by astronomy librarians to compile a thesaurus for inputting to and accessing computer database systems.

Molecular ices are a common component of the dust in many molecular clouds and circumstellar shells. The most abundant molecule, H2O, has several infrared spectral features which have strongly temperature dependent shapes (FWHM) and peak wavelengths. This paper describes how a study of these features, both astronomically and in the laboratory, can lead to constraints on the temperatures of interstellar dust grains. This is demonstrated in part by comparing several astronomical spectra with laboratory spectra of H2O ice.

The ideas and work presented in this paper date almost entirely from 1977 when the original paper was submitted. The referee suggested that we check out several other strong northern candidates before publication, but upon resubmission several years later the editor noted that as it was now accepted that DA,F white dwarfs did not exist there was little point in publishing the paper. In view of the fact that our preprint was the main stimulus for this status change and reference to this work remains ‘1977 unpublished’, we would like the paper to be published and thus complete the historical record.

Observations of some of the stars considered by Weidemann as the most likely DA,F candidates are discussed together with theoretical computations of white dwarfs and subdwarfs. The reddest stars BPM 23251 and G 82–23 are shown to be K subdwarfs and L 532–81 (EG62) is a DA white dwarf. It is suggested that the DA,F stars, if they exist at all, are extremely rare and that the metal abundance of the DA sequence may be less than 10–74 of the solar abundance.

We report on an initial survey of the cores of the Rho Ophiuchus and R Coronae Australis clouds, made with the AAT’s new IR array camera, IRIS. No turnover is seen in the initial luminosity function for ρ Oph to the sensitivity limit of the survey. Some implications for the low mass end of the initial mass function are discussed.

From extensive spectroscopic observations we derive the three-dimensional structure of the Homunculus Nebula surrounding η Carinae. The analysis shows that the two lobes are hollow and incomplete, and that the gas was ejected at similar epoch. Consequently the distribution of material we see reflects its initial velocity. Using the observed expansion velocity, and the known time of ejection, we derive a distance to η Car of 2.2 ± 0.2 kpc.

The star-formation process is an outstanding and largely unsolved problem in astrophysics. The role of magnetic fields is unclear but is widely considered to be important at all stages of protostellar evolution, from cloud collapse to ZAMS. For example, in some hydromagnetic models, the field may assist in removing angular momentum, thereby driving accretion and perhaps bipolar outflows.

Spectropolarimetry between 8 and 13μm provides information on the direction of the transverse component of a magnetic field through the alignment of dust grains. We present results of 8–13μm spectropolarimetric observations of a number of bipolar molecular outflow sources, and compare the field directions observed with the axes of the outflows and putative disk-like structures observed to be associated with some of the objects. There is a strong correlation, though so far with limited statistics, between the magnetic field and disk orientations. We compare our results with magnetic field configurations predicted by current models for hydromagnetically driven winds from the disks around Young Stellar Objects (YSOs). Our results appear to argue against the Pudritz and Norman model and instead seem to support the Uchida and Shibata model.

We have designed a novel all-reflective optical system for an infrared camera. The camera gives a flat 5 arcminute field with a final focal ratio of f/2.5 when used at the f/15 focus of the Anglo-Australian Telescope (AAT). A 70mm diameter Fabry-Perot filter can be accommodated in a collimated beam, thereby giving narrow-band imaging capability. The design could readily be adapted to other telescopes and focal ratios. Its advantages are no chromatic aberration, no vignetting, no ghost images, low light-loss and excellent image quality.

The AAT’S new IR array camera, IRIS, has been used to image the Galactic Centre in the He I (2.058μm), H+ Br γ(2.166μm) and H2 1-0 S(l) (2.122μm) emission lines. The case is presented for UV-excitation of the molecular gas, as opposed to shocks.