The use of artificial neural networks (ANNs) as a classifier of digital spectra is investigated. Using both simulated and real data, it is shown that neural networks can be trained to discriminate between the spectra of different classes of active galactic nucleus (AGN) with realistic sample sizes and signal-to-noise ratios. By working in the Fourier domain, neural nets can classify objects without knowledge of their redshifts.

The Australia Telescope Compact Array has been used in two 6 km configurations to make 12 hour observations of the radio continuum structure of three spiral galaxies at 1380 MHz and 2378 MHz. Radio maps of NGC 1792, 6300 and 1097 are presented here, as part of a survey to find examples of anomalous radio structures in spiral galaxies.

Quasi-simultaneous optical/near-IR photometry is presented for a sample of 37 luminous optically selected QSOs drawn from the Large Bright QSO Survey. Most of the QSOs have decreased in brightness since discovery; this is expected in flux-limited samples. The continuum shape of most of the QSOs can be represented by a power law of the form F(v) ∝ v−0·3, but a few have softer (redder) continuum slopes.

The propagation of extragalactic particles within our Galaxy has been modelled. The flux of such particles is below the observed cosmic ray flux at most energies when their power-law spectrum is extrapolated back from the highest energies. Also, we expect that the propagation of extragalactic particles through static magnetic fields in the Galaxy will not result in a flux change to match the flux of particles measured here within the Galaxy. However, if we were to consider the observed cosmic rays to be of Galactic origin, there would be a remarkable similarity between the required Galactic injection flux and the extrapolated extragalactic flux. We consider here whether the scattering of extragalactic particles in the Galaxy together with an associated energy perturbation might be sufficient for the extragalactic beam to result in the production of ‘Galactic’ particles and, hence, essentially all of the observed cosmic rays. This appears to be possible.

The dry, cold, tenuous and stable air above the Antarctic Plateau provides superb conditions for the conduct of many classes of astronomical observations. We review in particular the rationale for undertaking near-IR, mm and particle astronomy in Antarctica, disciplines where telescopes are now operating at the US Amundsen-Scott South Pole Station.

The giant radio galaxy B1308–441 has prominent two-sided jets, typical of Fanaroff–Riley class I radio galaxies, but there is an unusual bright spot in the SE jet 2 arcmin from the core that gives a marked asymmetry to the source. Observations at 1·37 and 2·37 GHz with the Australia Telescope Compact Array show that the bright spot has a flattened spectrum and high polarisation, and changes the direction of the SE jet. There is a diffuse optical object close to the bright spot which may be related to a shock in the jet.

The very low background observed from Antarctica in a window from about 2·25 to 2·45 μm can be exploited as a way of making deep near-IR surveys over wide areas of sky. Imaging surveys using the entire window can cover large areas of sky to limits of around K = 20, and can be used to study galaxy evolution and to search for high-redshift quasars, dust-obscured quasars and brown dwarfs. It is also possible to make spectroscopic surveys in this window. The window includes molecular hydrogen emission and CO absorption in galactic sources, and can also be used to search for emission lines such as Hα in high-redshift star-forming galaxies.

We have used a sample of 263 Parkes half-Jansky flat-spectrum radio sources to measure the spatial correlation function of radio galaxies and radio-loud quasars on scales up to 1000 h−1 Mpc. We do not detect any clustering in the sample. If any undetected clustering is described by a power-law spatial correlation function [ξ(r) = (r/r0)−1·8], we can rule out clustering with scales r0 ≥ 50 h−1 Mpc at the 99·9% confidence level. We have also used the sample to test for the ‘possible’ large concentration of quasars in the direction of the microwave background dipole found by Shaver (1987). There is no evidence for such a concentration in our data and we show that the earlier result was probably biased by the use of non-uniform image classifications.

This paper presents a new Lagrangian approach to the numeric solution of the equation of gas dynamics in two dimensions. This, the signal method, is implemented here as a free Lagrange method in the code FLAME. The signal method is conservative, stable, unsplit, positive definite, accurately tracks strong shock fronts with ease, and adapts to and follows complex gas flows for long times. No artificial viscosities are introduced. No special knowledge of the solution is required in advance and only local information is used.

Among the astrophysical researches which will largely benefit from observation from the Antarctic Plateau, we consider those which require high-quality, continuous, daylight, uninterrupted observation in the optical–near-IR region. The systematic study of the stellar micro-oscillations and surface activity of individual objects, as well as of stellar associations extended for periods of weeks, will make a fundamental contribution to our knowledge of stellar structure and will ultimately provide the physical parameters of the stars. A similar consideration applies for the short-period (a few hours to a few days) binaries, which include the W UMa contact binaries. These objects are subject to continuously varying light curves associated with surface activity and secular effects, which cannot be adequately studied from the currently available ground telescopes. Finally, the exceptional seeing and low background will allow the systematic search for and study of supernovae in clusters of galaxies at cosmological distances, which will improve our knowledge of the geometry of the Universe at z ~ 0·7–1.

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.

Gravitational lensing can significantly magnify the images of astrophysical sources, but only if the source lies within the Einstein ring of the lens. In consequence the chance of any Galactic star magnifying a more distant source is extremely small—much less than one in a million. However, the extra light travel time (‘Shapiro delay’) introduced by the presence of a lens can be large even when there is negligible effect on the image magnification, and as the relative positions of source and lens change so does the delay. In this paper we quantify these changes and the corresponding influence on apparent timing properties of pulsars. While the total Shapiro delay can be large, it is the temporal variations in this quantity which are measurable with pulsar timing. We find that the magnitude of the expected delay variations is too small to be detectable except during strong lensing events, which are extremely rare. Even in the case of a high-velocity pulsar in the Galactic Plane, the stochastic Shapiro delay is typically expected not to have a substantial influence on the timing properties. In consequence the viability of a pulsar-based time standard is not adversely affected by gravitational lensing.

The possibility is considered that core emission in pulsars results from secondary e± pairs generated through linear acceleration emission (LAE), rather than the conventional curvature emission (CE). It is found that this is possible in principle, but only under conditions that appear not to be satisfied in practice.

The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) is a highly automated 1·7 m diameter telescope aimed at exploiting the superb submillimetre skies of the Antarctic Plateau for astronomy and aeronomy studies. It was recently installed at the Amundsen-Scott South Pole Station during the 1994/95 Austral season and is currently undergoing its first winter-over of operation. In this paper we briefly outline the capabilities of the instrument and describe some recent achievements culminating in the telescope’s first observations of the South Polar submillimetre sky.

Several extragalactic HI surveys using a λ21 cm 13-beam focal plane array will begin in early 1997 using the Parkes 64 m telescope. These surveys are designed to detect efficiently nearby galaxies that have failed to be identified optically because of low optical surface brightness or high optical extinction. We discuss scientific and technical aspects of the multibeam receiver, including astronomical objectives, feed, receiver and correlator design and data acquisition. A comparison with other telescopes shows that the Parkes multibeam receiver has significant speed advantages for any large-area λ21 cm galaxy survey in the velocity range range 0–14000 km s−1.

A software package called ERIC is described that provides a framework for allowing scientific instruments to be remotely controlled via the Internet. The package has been used to control four diverse astronomical instruments, and is now being made freely available to the community. For a description of ERIC’s capabilities, and how to obtain a copy, see the conclusion to this paper.

Expressions for the probability per unit time of the emission of a Langmuir wave by both massive and massless neutrinos moving in a medium are derived using finite-temperature field theory. A comparison between this process and the analogous emission from an electron is made, and possible implications of this process for the explosion mechanisms of type II supernovae are briefly discussed.

The Sydney University Stellar Interferometer (SUSI) uses siderostats (plane, alt–azimuth mounted mirrors) to reflect starlight into the instrument. The analysis of the pointing and guidance of the siderostats by traditional methods is not practical and vector algebra has been used to develop the required algorithms. Real siderostats will not be ideal and can be modelled by a set of parameters. The methods for determining the model parameters and for incorporating them into the guidance and pointing algorithms are described. Field rotation also affects the operation of SUSI, and the field rotation angle and related quantities are also determined.

We describe the use of a multi-aperture Hartmann mask coupled to a slightly out-of-focus focal plane array imager to monitor atmospheric turbulence (‘seeing’) produced by refractive index fluctuations. The imager (a CCD) is located inside or outside the focal surface of the imaging system so that each sub-aperture of the Hartmann mask produces an image well separated from all of the other images produced by the mask. Since the depth of focus of the sub-apertures is an order of magnitude larger than that of the parent optical system, the individual images are still diffraction-limited. We obtain short (10 to 100 msec) exposures and monitor the position fluctuations of the images. Analysis of the position and intensity fluctuations of the images can be used to determine the atmospheric parameter r0, the wind direction and velocity, and, under some circumstances, the distance of the turbulent layer from the observing site.