The development of long-baseline optical interferometry in Australia from the Narrabri Stellar Intensity Interferometer (NSII) to the Sydney University Stellar Interferometer (SUSI) and the resulting technical and scientific achievements are described. Three examples of results from the SUSI programme, for a single star, a double-lined spectroscopic binary, and a Cepheid variable, are presented to illustrate the advances made in the past four decades. The leading role that Australia has played in the development of the field worldwide is discussed from a personal viewpoint. Long-baseline optical interferometry has promised much, has been slow to deliver, and has been restricted to black-belt interferometrists, but it has now matured to the point where it is becoming an observational technique for astronomers in general.

To maximise data output from single-shot astronomical images, the rejection of cosmic rays is important. We present the results of a benchmark trial comparing various cosmic ray rejection algorithms. The procedures assess relative performances and characteristics of the processes in cosmic ray detection, rates of false detections of true objects, and the quality of image cleaning and reconstruction. The cosmic ray rejection algorithms developed by Rhoads (2000, PASP, 112, 703), van Dokkum (2001, PASP, 113, 1420), Pych (2004, PASP, 116, 148), and the IRAF task XZAP by Dickinson are tested using both simulated and real data. It is found that detection efficiency is independent of the density of cosmic rays in an image, being more strongly affected by the density of real objects in the field. As expected, spurious detections and alterations to real data in the cleaning process are also significantly increased by high object densities. We find the Rhoads' linear filtering method to produce the best performance in the detection of cosmic ray events; however, the popular van Dokkum algorithm exhibits the highest overall performance in terms of detection and cleaning.

Donations (in cash and kind) amounting to $200,000 from companies in the south-western Sydney region have allowed the construction of a teaching, research and public access Observatory at the University of Western Sydney in Campbelltown. The Observatory will also serve as the home of the Australian Optical SETI Project (OZ OSETI for short). Two fibre-glass domes will be installed at the site. The main 4.5 m fibre-glass dome will house a 0.4 m telescope while the smaller 2.9 m dome will house a 0.3 m telescope. Both telescopes are fork-mounted Schmidt-Cassegrains working at f/10. An outside observation area will be used for tripod-mounted telescopes for public use and teaching purposes. The expected completion date for the project is July 2000.

We investigate the present distributions of gas and young stars in the Large and Small Magellanic Clouds (LMC and SMC) based on fully self-consistent numerical simulations of the Clouds for the last ∼0.8 Gyr. Our principal results, which can be tested against observations, are as follows. The last dynamical and hydrodynamical interaction between the Clouds about ∼0.2 Gyr ago can form the apparently off-center bar and peculiar Hı spirals of the LMC. The present spatial distributions of young stars with ages less than ∼20 Myr in the LMC can be significantly asymmetric and clumpy owing to the interaction. A small but non-negligible fraction of stellar and gaseous components can be transferred from the SMC into the LMC during the interaction to form diffuse halo components around the LMC. The burst of star formation in the SMC can be synchronized with that of the LMC about 0.2 Gyr ago in some models. New stars can form from gas in the SMC's tidal tails, one of which can be observed as the Magellanic Bridge (MB). The metallicity distribution function of new stars in the MB has a peak of [Fe/H] ∼ −0.8, which is significantly smaller than the stellar metallicity of the SMC. Based on these results, we discuss the origin of 30 Doradus, the southern molecular ridge of the LMC, the globular cluster ESO 121-SC03, metal-poor inter-Cloud stars within the MB, and giant Hı holes of the LMC.

I shall present a series of easy demonstrations that can be carried out during formal astronomy lectures. Since astronomy is physics we have developed on Earth applied to celestial objects, there are many useful experiments that can be carried out with relative ease by physics teachers in order to help pupils grasp the workings of the universe and to relate them with every day experiences. One of the difficulties in teaching science is that we use two-dimensional pictures to explain a three-dimensional reality. Using models helps students understand some of the properties of celestial objects. Although it is important to have pupils experiment on their own, some demonstrations are so simple that it is enough to have the teacher carry them out during the lecture to have pupils grasp their importance or at least keep their attention focused on the topic at hand. The demonstrations can be used in elementary education as well as in introductory astronomy courses and teacher workshops.

We used an Artificial Neural Network (ANN) to derive the orbital parameters of spectroscopic binary stars. Using measured radial velocity data of seven double-lined spectroscopic binary systems V373 Cas, V2388 Oph, V401 Cyg, GM Dra, V523 Cas, AB And and HD 141929, we found corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by others using more traditional methods.

The photometric observations (UBVRI) of nine cool R Coronae Borealis (RCB) stars have been collected at Mt John University Observatory, New Zealand, over a period of twelve years. The analysis of the magnitude–colour and colour–colour diagrams for the recovery phase demonstrates that all declines exhibit a similar asymptotic approach to their normal brightness. Declines return to maximum brightness along a line with essentially the same slope that does not depend on the star or the depth of the decline. Assuming a uniform obscuration of the photosphere by the dust cloud during the recovery phase, the extinction properties of the material were determined. The ratio of total to selective extinction (R V) for the RCB stars in our sample is in the range 2.5 to 4.6, indicating that the obscuring dust has extinction properties similar to that of the interstellar dust. Observations have been compared with the theoretical extinction curves for different sorts of grains.

A model for the energetics of solar flares, developed by Melrose (1997), is based on magnetic reconnection between two current-carrying magnetic loops. A detailed numerical investigation of the model has been made to identify those configurations that lead to energy release in a flare. Our results predict a strong relation between the ratio of currents in the interacting loops for a favoured flare configuration, and provide further support for a proposed method of generating long loops connecting different active regions. Both of these predictions are amenable to observational verification.

Based on the free–free absorption (FFA) model of gigahertz peaked spectrum (GPS) sources, we explain both Faraday rotation asymmetry and opacity asymmetry consistently between two components of a GPS quasar 2134+004. The FFA model assumes dense plasma around the central core to produce FFA, and the difference of path lengths in the plasma toward each component could cause these asymmetries. The component that is closer to the observer has a shorter path length, and consequently, smaller opacity of FFA and lower Faraday rotation. In a simple case, the ratio of Faraday rotation between two components is a function of the ratio of path length, and is the same as the ratio of opacity. Then these two ratios are shown to be essentially the same by our observations. We could thus distinguish between near-side and far-side components by the asymmetries.

In conjunction with the Australian Government's Spectrum Management Agency, experimental tests have been carried out to determine the susceptibility of the Molonglo Observatory Synthesis Telescope (MOST) to interference from terrestrial transmitters. The motivation for the tests was to reconcile the conflicting requirements of the MOST, which is committed to an extensive survey of the southern sky at 843 MHz, with the commercial use of the 825–845 MHz band, which is being prepared for sale. The tests show that the far sidelobe gain of the MOST, relative to an isotropic antenna is generally less than 1, and that an appropriate interference criterion would be that in-band interference irradiance should not exceed −173 dBWm−2. This value is similar to that considered by the International Telecommunications Union to be detrimental to radio astronomy continuum observations at nearby frequencies.

We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard ΛCDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ‘observable universe’ and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23σ.

Digital images were made of Bamberg Observatory Sky Patrol plates of the field surrounding the active-chromosphere star CF Octantis (HD 196818). These images, taken with an inexpensive camera, were analysed using standard aperture photometry techniques. Good agreement was found with catalogued photographic magnitudes for stars in the range m pg ∼8.5 to ∼10.5. The root-mean-square deviations in the measured differences for non-variable field stars was found to be of order 0.10 mag, although a small number of larger differences occurred. For CF Oct, a period search of data from 1966 recovered the known 20 d variation due to starspot rotational modulation, with a range of variation of order 0.5 mag photographic. For active-chromosphere stars with moderately large photometric variations (>∼0.3 mag), and moderate to long rotation periods (>∼1 week), careful analysis of similarly obtained digital copies of archive plates may provide valuable insights into historical actvity.

Satellite cloud imagery is a standard tool of meteorology, and also of ground-based observational astronomy. Fast access to cloud imagery through the Internet now permits more accurate prediction of local cloud cover than was formerly the case. This is particularly useful for automatic and remotely operated telescopes, where an observer may be at a considerable distance from the telescope itself. Since satellite imagery can now be accessed through the Internet with such ease, direct reception of radio transmissions from weather satellites may seem unnecessary. However, advances in computing power and radio receiver technology permit simple automated receipt of satellite transmissions, particularly from the NOAA series of low Earth orbit satellites. This has the advantage of more up-to-date, and higher resolution, cloud imagery than can be obtained from the Internet. We have operated such a satellite receiving station since 2003 April, and have found it particularly useful when remotely operating our telescopes at Siding Spring Observatory (SSO). By automatically publishing our cloud imagery onto the World Wide Web we have established a resource that is widely used by other local observatories and by the general public.

This paper is a preliminary report on ongoing work, in collaboration with Drs S. P. Goodwyn, A. J. Mestel, and G. A. E. Wright. The non-dissipative force-free condition should be a good approximation to describe the electromagnetic field in much of the pulsar magnetosphere, but we may plausibly expect it to break down in singular domains. The detailed properties of the solutions will be affected critically by the choice of equatorial boundary condition beyond the light-cylinder.

We follow the chemical evolution of the Galaxy for the s elements using a Galactic chemical evolution (GCE) model, as already discussed by Travaglio et al. (1999, 2001, 2004), with a full updated network and refined asymptotic giant branch (AGB) models. Calculations of the s contribution to each isotope at the epoch of the formation of the solar system is determined by following the GCE contribution by AGB stars only. Then, using the r-process residual method we determine for each isotope their solar system r-process fraction, and recalculate the GCE contribution of heavy elements accounting for both the s and r process. We compare our results with spectroscopic abundances at various metallicities of [Sr,Y,Zr/Fe], of [Ba,La/Fe], of [Pb/Fe], typical of the three s-process peaks, as well as of [Eu/Fe], which in turn is a typical r-process element. Analysis of the various uncertainties involved in these calculations are discussed.

A search for planetary nebulae was carried out using candidates selected by their infrared colours and 5 GHz radio emission. One new planetary nebula was identified on the basis of its small angular size, strong [O iii] emission and infrared colours. Another object, known as the possible planetary nebula Wray 16–28, is similarly identified as a planetary nebula. An undiscovered AGN was also found, and is classed as a Seyfert 2 galaxy on the basis of its strong O iii emission, linewidths of ∼500 km s−1, and 5 GHz radio flux. Low-resolution optical spectra are presented and distance estimates discussed.

Editing radio interferometer data, a process commonly known as ‘flagging’, can be laborious and time-consuming. One quickly tends to flag more data than actually required, sacrificing sensitivity and image fidelity in the process. I describe a program, PIEFLAG, which can analyze radio interferometer data to filter out measurements which are likely to be affected by interference. PIEFLAG uses two algorithms to allow for data sets which are either dominated by receiver noise or by source structure. Together, the algorithms detect essentially all affected data whilst the amount of data which is not affected by interference but falsely marked as such is kept to a minimum. The sections marked by PIEFLAG are very similar to what would be deemed affected by the observer in a visual inspection of the data. PIEFLAG displays its results concisely and allows the user to add and remove flags interactively. It is written in python, is easy to install and use, and has a variety of options to adjust its algorithms to a particular observing situation. I describe how PIEFLAG works and illustrate its effect using data from typical observations.

We summarise the HI properties of early-type galaxies, in particular the differences in HI morphologies observed in early-type galaxies of different luminosities. We find that in low-luminosity early-type galaxies the HI is almost always in a disk-like structure, with central surface densities high enough for star formation to occur. In a few luminous early-type galaxies the HI is also in a disk or in a ring-like structure, but in most luminous early-type galaxies the HI has a relatively irregular morphology. The surface densities in the HI disks in luminous early-type galaxies are lower than in the HI disks in low-luminosity early-type galaxies and no large-scale star formation should occur in these disks. We discuss these different HI characteristics in the context of other properties of early-type galaxies that correlate with luminosity.

This paper investigates a recent model proposed by Moskalenko, Collmar & Schönfelder (1998) for the plasma surrounding galactic black hole candidates. Using a linear Monte Carlo code, the spectral and temporal behaviour of the model is found for the case where the plasma geometry consists of a hot shell surrounding a cooler spherical core. The spectrum produced by this model at X-ray and gamma-ray energies is obtained numerically. Also found for the first time in this geometry are the photon time-lags between two energy bands due to rapid aperiodic variability. It is argued that the time-lag information may be able to determine whether this particular geometry is a realistic model for the material surrounding galactic black hole candidates.