Analyses of QSO absorption lines show that the HI content has evolved over the redshift range z = 5 to z = 0. The 21-cm line measurements of the z = 0 HI content avoid several biases inherent in the absorption-line technique, such as the influence of evolving dust content in the absorbers, and will produce a reliable measure to anchor theories of galaxy evolution. Examples of important questions to be addressed by local HI surveys are: (1) Is there a significant population of gas-rich galaxies or intergalactic clouds that is missing from the census of optically selected galaxies? (2) Is there an adequate reservoir of neutral gas to substantially prolong star formation at its present rate? (3) Are there massive objects of such low HI column density that they can have escaped detection in the ‘unbiased’ HI surveys that have been conducted so far?

We present IIIaJ, IIIaF and IVN band images of HH objects digitised from the ESO/SERC Southern Sky Survey plates. These form part of a digital image database of southern HH objects, which allows the identification of emission and reflection nebulosity and the location of the obscured sources of outflows.

As an experiment, special holiday programs for primary school children were offered by the Carter Observatory during two different school holidays in 1995. One program focussed on Mars and the other on the Sun. This paper describes the two programs, expands on their strengths and weaknesses from different viewpoints, and (despite their overwhelming popularity) outlines the reasons why the Observatory has decided not to offer further holiday programs of this type in the foreseeable future.

Driftscan methods are highly efficient, stable techniques for conducting extragalactic surveys in the 21 cm line of neutral hydrogen. Holding the telescope still while the beam scans the sky at the sidereal rate produces exceptionally stable spectral baselines, increased stability for RFI signals, and excellent diagnostic information about system performance. Data can be processed naturally and efficiently by grouping long sequences of spectra into an image format, thereby allowing thousands of individual spectra to be calibrated, inspected and manipulated as a single data structure with standard tools that already exist in astronomical software. The behaviour of spectral standing waves (multi-path effects) can be appraised and excised in this environment, making observations possible while the Sun is up. The method is illustrated with survey data from Arecibo and Nançay.

A radio spectrometer has been built on Bruny Island, south of Hobart, for the study of solar bursts in the rarely observed frequency range from 3 to 20 MHz. This spectrometer is an adaptive device that employs digital techniques to avoid most of the strong terrestrial interference prevalent in this frequency range. The residual interference that cannot be avoided is excised during off-line processing. As a result, successful observations are made down to the minimum frequency that can propagate through the ionosphere to the antenna. This minimum frequency depends upon the zenith distance of the Sun and it is usually between 4 and 8 MHz.

Traditional HI surveys of optically selected elliptical galaxies are time-consuming, and have a low detection rate. The forthcoming Parkes HI multibeam survey offers the exciting possibility of surveying more than 10,000 nearby elliptical galaxies for HI. I argue that this is likely to result in the detection of a large population of small, HI-rich elliptical galaxies which have not previously been studied in any systematic way.

Cosmic radiation is capable of depositing significant quantities of energy and momentum in gravitational wave antennas at times that will generally be random with respect to gravitational signals. Such cosmic ray effects may generate noise signals at detectable levels compared to antenna design thresholds at rates of a few per year but, since antennas will not be capable of absorbing all the cosmic ray energy, it should be readily possible to construct vetoing cosmic ray detectors. For proposed interferometer antennas, a deposition of a few hundred GeV will produce a detectable noise signal and the veto will require about 100 MeV of energy deposition outside the antenna. We consider here some of the principles involved in the generation of gravitational antenna noise by cosmic ray particles and we describe a veto system to be installed at the Perth gravitational wave observatory.

Stability of accretion onto magnetic white dwarfs is investigated via perturbation analysis. We consider a cooling function with composite power laws, and the power-law indices are appropriate for bremsstrahlung and optically thick cyclotron cooling. We find that the presence of cyclotron cooling generally suppresses the instability, consistent with numerical simulations by other investigators.

We present preliminary results from HI observations of a new sample of compact groups done with the Parkes telescope, as well as from images made with the Australia Telescope Compact Array (ATCA). These observations confirm earlier claims that a significant fraction of compact groups are deficient in HI, and hence that a significant fraction of groups of galaxies that appear compact on the sky are indeed compact systems. The ATCA observations of a very HI-poor group suggest that this group is a true compact system in an advanced stage of evolution. However, the ATCA observations also show that HI-rich groups exist that are genuinely compact.

The few elliptical galaxies with detected HI almost all seem to have optical peculiarities as well, though these are often well hidden and require special image enhancement techniques to reveal them. In this paper we show several deep images of ellipticals with optical shells which are associated with HI, and suggest that mergers, or at least encounters with gas-rich galaxies, are responsible. We also show some disk galaxies with unusual faint extensions, some of them the kinds of interactions that may result in HI in ellipticals. These illustrations are drawn from an atlas of low surface brightness images of bright galaxies currently in preparation.

Although a number of correlations have been demonstrated between observable parameters in galaxies, such as surface brightness, luminosity, metallicity, etc., debate continues as to which of these parameters are truly fundamental. Following a major surface photometry program and Hii region abundance analysis, we have been able to show that the surface density of recent massive star formation, the surface density of stars already formed, and the mean oxygen abundance at a given galactic radius are all fundamentally related within and between the disks of spiral galaxies. Such relationships can serve as powerful constraints on models of galactic evolution, requiring, for instance, a star formation law dependent not only on gas surface density, but also on the total mass surface density.

There has been much debate in recent decades as to what fraction of ionising photons from star-forming regions in the Galactic disk escape into the halo. The recent detection of the Magellanic Stream in optical line emission at the CTIO 4 m and the AAT 3·9 m telescopes may now provide the strongest evidence that at least some of the radiation escapes the disk completely. We present a simple model to demonstrate that, while the distance to the Magellanic Stream is uncertain, the observed emission measures (εm ≈ 0·5 – 1 cm−6 pc) are most plausibly explained by photoionisation due to hot, young stars. This model requires that the mean Lyman-limit opacity perpendicular to the disk is τLL ≈ 3, and the covering fraction of the resolved clouds is close to unity. Alternative sources (e.g. shock, halo, LMC or metagalactic radiation) contribute negligible ionising flux.

Interferometric methods have been used at a number of observatories to improve the spatial resolution of large optical telescopes, approaching and in some cases reaching the diffraction limit. The principal methods used have been speckle interferometry and non-redundant masking (NRM). The MAPPIT (Masked APerture Plane Interference Telescope) instrument has been used for NRM observations at the 3·9 m Anglo-Australian Telescope. This paper describes a proposed instrument, MAPPIT 2, which would use a Shack-Hartmann wavefront sensor in parallel with an interferometer performing NRM or one-dimensional speckle interferometry. The inclusion of the data from the wavefront sensor will enhance the sensitivity of the instrument, especially for the imaging of relatively complex objects (those giving more than a few resolution elements with non-zero intensities). Limiting the instantaneous spatial resolution to one dimension allows available CCD detectors to operate with 100% duty cycle. Observations at a number of position angles allow two-dimensional images to be obtained.

We summarise recent attempts to detect warm ionised gas at large galactocentric distances. This includes searches for gas at the edges of spirals, in between cluster galaxies, towards extragalactic HI clouds, and towards high-velocity clouds and the Magellanic Stream in the Galaxy. With the exception of extragalactic HI clouds, all of these experiments have proved successful. Within each class, we have only observed a handful of objects. It is premature to assess what fraction of the missing baryonic mass fraction might be in the form of ionised gas. But, in most cases, the detections provide a useful constraint on the ambient ionising flux, and, in the case of spiral edges, can even trace dark matter haloes out to radii beyond the reach of radio telescopes.

We review very strong selection effects which operate against the detection of dim (i.e. low surface brightness) galaxies. The Parkes multibeam instrument offers a wonderful opportunity to turn up new populations of such galaxies. However, to explore the newly accessible parameter space, it will be necessary to survey both a very deep patch (105 s/pointing, limiting Nhi ∼ 1018 cm−2) and a deep patch (104 s/pointing, limiting Nhi ∼ 3 × 1018 cm−2) in carefully selected areas, and we outline the case to do this.

The Molonglo Observatory Synthesis Telescope (MOST) has been upgraded to increase the diameter of the field of view from 70′ to 2·7°. A survey of the Galactic Plane is proposed to completely cover the region 240° ≤ l ≤ 365°, ∣ b ∣ ≤ 10° with a (1σ) sensitivity of 1–2 mJy. The results will provide a major resource for the investigation of supernova remnants, HII regions and transient radio sources. They will also be correlated with the galaxy search from the HI multibeam survey to be conducted at the Parkes telescope.

Recent results on NGC 2915, the first blue compact dwarf galaxy to have its mass distribution modelled, are summarised. NGC 2915 is shown to have HI well beyond its detected optical extent. Its rotation curve is well determined and fit with maximum disk mass models. The dark matter halo dominates the mass distribution at nearly all radii, and has a very dense core compared to those of normal galaxies. High-mass star formation energises the HI in the centre of the galaxy, but appears to be maintained in viriai equilibrium with the dark matter halo. The implications of these results are briefly discussed.

NGC 7421 is a barred spiral that is displaced from the centre of its optical envelope, and has a ‘bow-shock’-like western boundary, both suggestive of interaction with an intracluster medium. We have used five configurations of the ATCA to map the distribution and kinematics of HI in NGC 7421, and find supportive evidence for this scenario in the form of an HI ‘wake’. When compared with ROSAT PSPC observations of the diffuse hot gas in the surrounding group of galaxies, these new ATCA results will allow us to place new constraints on the density and dynamics of the intracluster medium.

We have found strong evidence for an abrupt decline in the HI rotation curve of the isolated spiral galaxy NGC 157. Various mass models to account for this, and the implications for the dark matter content of NGC 157, are discussed.

We present HI images for the dust-lane elliptical galaxy NGC 5266. This galaxy contains more than 1010M☉ of HI and our data show that the neutral hydrogen extends to ∼8 arcmin each side of the nucleus, or eight times the optical half-light radius Re. Surprisingly, the outer HI gas extends almost orthogonally to the optical dust lane. The overall HI kinematics can be successfully modelled by assuming that the gas hes in two orthogonal planes—in the plane of the dust lane in the central parts and perpendicular to this in the outer regions. The large amount of neutral gas observed and the HI morphology suggest that this object may have formed from the merger of two gas rich spiral galaxies. If so, it probably represents a relatively old merger remnant since most of the HI appears settled. The mass-to-light ratio has also been derived, with evidence for a dark matter halo around this galaxy.