The coalescence of two Langmuir waves, L and L′, produces emission at twice the plasma frequency in type II and type III solar radio bursts. The analysis of the coalescence process is usually simplified by assuming the head-on approximation, where the wavevectors of the coalescing waves satisfy kL′ ≈ −kL, corresponding to the two Langmuir waves meeting head on. However, this is not always a valid approximation, particularly when the peak of the Langmuir spectrum lies at small wavenumbers, for narrow band spectra, and for spectra with broad angular ranges. Realistic Langmuir wave spectra are used to investigate the effects of relaxing the head-on approximation.

We present spectropolarimetric observations of the eclipsing cataclysmic variable 1H1752+08. Modelling of the line intensity and polarisation spectra of 1H1752+08 shows that the magnetic field structure of the white dwarf is off-centre and the mean photospheric field strength is about 7 MG, the lowest measured in a cataclysmic variable (CV). We argue that 1H1752+08 is most probably a low-field AM Herculis system.

Relative efficiencies for the discovery of Earth-crossing asteroids (ECAs) are modelled for various telescopes at Siding Spring. It is found that the narrow-field instruments—the Anglo-Australian Telescope and the 40 in and 2·3m reflectors—are not competitive in this regard for present CCD imaging systems. The UK Schmidt Telescope (UKST), if used to take short-exposure stereo pairs of photographs, would be an effective search tool, outperforming all current systems apart from the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) systems now being implemented by the US Air Force for ECA searches. If a CCD mosaic were fitted to the UKST, its performance would far exceed that of any other device at Siding Spring, and it would produce ECA discoveries at a rate around 3–4 times as high as GEODSS, but at considerable expense. The most sophisticated search instrument currently in use is the University of Arizona’s Spacewatch telescope; a notable result found here is that even with its present CCD, the Automated Patrol Telescope (APT) of the University of New South Wales would be able to match or outperform Spacewatch for all ECA sizes, including ~10m objects, should this modelling be a reasonable representation of its real performance. In terms of cost-effectiveness and telescope availability, the conclusion arrived at herein is that the APT, equipped with small-pixel but large-format CCD chips of high quantum efficiency, would be an extremely effective ECA search instrument: if operated with 12 μm pixel chips covering a 4° × 4° field it might produce ECA discoveries at a rate well in excess of the combined rate for all current search programs.

Three-wave interactions involving two high-frequency waves (in the same mode) and a low-frequency wave are discussed and applied to pulsar eclipses. When the magnetic field is taken into account, the low-frequency waves can be the ω-mode (the low-frequency branch of the ordinary mode) or the z-mode (the low-frequency branch of the extraordinary mode). It is shown that in the cold plasma approximation, effective growth of the low-frequency waves due to an anisotropic photon beam can occur only for z-mode waves near the resonance frequency. In the application to pulsar eclipses, the cold plasma approximation may not be adequate and we suggest that when thermal effects are included, three-wave interaction involving low-frequency cyclotron waves (e.g. Bernstein modes) is a plausible candidate for pulsar eclipses

Radio astronomy software has not quite kept up with recent developments for the display of, and interaction with, data. At the Australia Telescope National Facility we are trying to catch up by investigating how useful visualisation techniques and approaches like visual computing are for the reduction of radio data. I will discuss a few techniques that we have applied to radio data and comment briefly on their merits.

A recent study has indicated that a substantial fraction of young pulsars born in supernovae have travelled outside the boundaries of their corresponding shell supernova remnants. A simple model suggests that this should not be the case, implying either that some postulated pulsar/remnant associations are false, or that pulsars are particularly difficult to detect until they have emerged from their remnants.

We present near-infrared spectroscopic observations over the wavelength range 0·9 to 2·5 μm of the AM Herculis system BL Hyi. During these observations, broad and resolvable cyclotron emission harmonics were visible near 1·25, 1·60 and 2·20 μm. We have interpreted these features as arising from a cyclotron emission region located near the white dwarf’s polar cap of magnetic field strength Bp = 23 MG.

The X-ray Timing Explorer (XTE) is a NASA satellite designed to perform high-time-resolution studies of known X-ray sources. The two main experiments are a large-area proportional counter array (PCA) from the Goddard Space Flight Center (GSFC) and a high-energy X-ray timing experiment (HEXTE) from the University of California at San Diego (UCSD). The PCA data is processed by an electronic data system (EDS) built by the Massachusetts Institute of Technology (MIT) that performs many parallel processing analysis functions for on-board evaluation and data compression. MIT also provide an all-sky monitor (ASM) experiment so that XTE can be slewed rapidly to new transient sources. The spacecraft provides a mean science telemetry rate for the PCA of ~20 kilobits per second (kbps), with bursts to 256 kbps for durations of 30 minutes. Photons are tagged to 1 μs and absolute timing should be better than 100 μs. XTE is due for launch in late August 1995 and the first NASA Research Announcement (NRA) is due out in January 1995. This paper summarises XTE’s performance and then discusses the interactive and flexible operations of the satellite and some of the science it can do. These features should make XTE a productive spacecraft for coordinated observation programs.

Radio snapshot imaging is an efficient observing method which allows several sources to be observed in the one session. Snapshot observing with the Australia Telescope Compact Array (ATCA) involves special difficulties, as the small number of antennas combined with the short total integration time leads to high sidelobe levels in the raw images. The images can be improved markedly by standard deconvolution techniques, but more care is required in their use because of the difficulty in distinguishing real emission from artefacts. This study, based on a set of snapshot observations of strong sources at 5 GHz, gives guidance on both the planning of observations and the data reduction. We show that snapshot imaging with the 6 km ATCA can achieve a dynamic range of 100–200:1 provided certain conditions are met, namely a peak flux density > 100 mJy, an angular size ≤ 30″ and an hour-angle coverage spanning at least six well-separated 5-minute cuts. When observing weak sources it is essential for calibration sources to be selected carefully and observed frequently.

We resolve a conflict in the literature concerning the effect of induced Compton scattering on the propagation of radio waves through the electron–positron wind surrounding a pulsar.

We have developed an easy-to-use, mouse-driven program for the interactive fitting of interstellar absorption lines in high-resolution astronomical spectra. The program, Xvoigt, gives values for the column density and velocity dispersion of the absorbing clouds. It runs under the popular X Window system available on most workstations, and offers significant enhancements over existing profile-fitting software. Xvoigt can be an important adjunct to automatic programs for fitting absorption lines in low to moderate signal-to-noise QSO or other spectra, and is ideal for demonstrating the details and difficulties of absorption line analysis.

Recent seeing measurements at the Anglo-Australian Telescope (AAT) point towards the thermal characteristics of the telescope itself, in particular the temperature difference between the mirror and the dome air, as the most important factor degrading the seeing, more so than the temperature difference between the inside and outside air. We present the findings, propose clarifying experiments, and discuss possible remedies. We set the realistic target for the AAT to achieve median seeing of 1·5″ rather than the current 1·8″.

The Figaro data reduction system was originally written for DEC VAXes running VMS, and little attention was paid to making it portable. Recently, however, a cooperative effort between the AAO, MSSSO, UNSW, the UK Starlink network and Caltech has resulted in a version for UNIX. This new version has been run under VMS and three different versions of UNIX. The files produced by any version may be read directly by any other version, although Figaro has a particularly complex file format which contains an extensible, self-defining, hierarchical structure of data items. This complexity has allowed the addition of error and quality data, as well as specific structures used, for example, for echelle data. Figaro is written mainly in Fortran (with numerous DEC extensions) but there is also a significant use of C. While C and Fortran are reasonably portable, the way one is called from the other is less portable and needs careful handling. Ports to other systems are possible, with effort; a Macintosh version is being considered.

Seeing measured in the open air with a differential image motion monitor (DIMM) is compared with seeing measured simultaneously at the Cassegrain focus of the Anglo-Australian Telescope (AAT). It is shown that when the mirror is hotter than the dome air, the AAT’s seeing is degraded by ~1 arcsec per Celsius degree of excess mirror temperature. The consequence of this is that mirror seeing currently contributes significantly to the seeing at the AAT on many nights. A mirror colder than the dome air does not seem to degrade seeing, and neither does an internal-to-external air temperature difference of up to at least 3°C when the venting fans are on.

A low-cost differential image motion monitor (DIMM), consisting of an 11-inch Celestron, an SBIG ST-4 autoguiding CCD camera and a PC, is described. Two such systems were used during June–July and November–December 1993 to make near-simultaneous seeing measurements at Freeling Heights in the Northern Flinders Ranges and at Siding Spring Observatory. The results of these campaigns show that the seeing-distribution is generally similar at both sites, with the most common seeing value being ~l·2″. Siding Spring does, however, have slightly more bad seeing (>2″) than Freeling Heights. Weather records from Arkaroola Resort (15 km south of Freeling Heights) indicate that there is ~15% less cloud cover at Freeling Heights than at Siding Spring. Episodes of rapid seeing deterioration at Siding Spring in winter are shown to coincide with warm air masses crossing the mountain.

A complete copy of the compressed COSMOS/UKST Southern Sky Object Catalogue is now available on-line at the Anglo-Australian Observatory and the Australia Telescope National Facility. The catalogue lists image parameters for all objects detected to a limit of BJ ≈ 21·5 in the UK Schmidt Southern Sky Survey. We have written software to access the catalogue efficiently and generate finding charts or text listings of the image parameters. In this paper we describe the software and give some examples of its use. We also discuss the astrometric precision of the catalogue.

A consortium of Australian universities and the Anglo-Australian Observatory is currently implementing an adaptive optical system at the Anglo-Australian Telescope. This project aims to enhance the science output of the telescope and establish the utility of adaptive optics at the AAT site. The first stage of the project is a fast tip-tilt system, described here, to be installed in the west coudé room. Subsequent funding has been obtained to implement a second-stage, low-order deformable mirror system which is also outlined. Both phases will primarily serve the IRIS camera/spectrograph, since the maximum gains in image quality will occur in the infrared.

This paper is based on a report given at the ASA Conference in July 1994, but takes account of subsequent developments up to the end of the year. The present state of the Two-degree Field (2dF) project for the AAT is reported. Good progress is being made on all fronts but some slippage has occurred, so that the instrument is now expected to begin astronomical observations only during the second half of 1995. An outline of other current and future instrumentation plans at the AAO is given.

A Dark Matter Workshop was held at the CSIRO Radiophysics Laboratory in Marsfield, Sydney, on 24–25 February 1994. The workshop, sponsored by the Australia Telescope National Facility (ATNF), was a meeting of dark matter (DM) specialists as well as astronomers interested in the field, and attracted about 80 participants from nine institutions. The program consisted of 22 oral contributions (15–45 minutes), followed by lively discussions, as well as podium discussions at the end of each day. Abstracts of most of the contributions are presented here, arranged by subject groups which range from ‘Gravitational Lensing and DM in Clusters’, ‘DM in Elliptical Galaxies’, ‘The Nature of DM’, and ‘The Shapes of Dark Halos’ to ‘Alternatives to DM’.