The effect of nonaxisymmetric radiation drag on relativistic jets in active galactic nuclei (AGN) is discussed. The radiation force due to inverse Compton scattering of photon fields from a noncircular accretion disk is calculated. It is shown that such nonaxisymmetric drag can cause jet path distortion within the subparsec region of the black hole. This subparsec scale distortion is potentially observable with the current VLBI, VLBA techniques. Any modulation of the axially asymmetric distribution of disk emission can result in variability in electromagnetic radiation from the jet.

We measure the spectral properties of a representative sub-sample of 187 quasars, drawn from the Parkes Half-Jansky, Flat-radio-spectrum Sample (PHFS). Quasars with a wide range of rest-frame optical/UV continuum slopes are included in the analysis: their colours range over 2 < B–K < 7. We present composite spectra of red and blue sub-samples of the PHFS quasars, and tabulate their emission line properties.

The median Hβ and [O III] emission line equivalent widths of the red quasar sub-sample are a factor of ten weaker than those of the blue quasar sub-sample. No significant differences are seen between the equivalent width distributions of the C IV, C III] and Mg II lines. Both the colours and the emission line equivalent widths of the red quasars can be explained by the addition of a featureless red synchrotron continuum component to an otherwise normal blue quasar spectrum. The red synchrotron component must have a spectrum at least as red as a power-law of the form Fυ α υ−2.8. The relative strengths of the blue and red components span two orders of magnitude at rest-frame 500 nm. The blue component is weaker relative to the red component in low optical luminosity sources. This suggests that the fraction of accretion energy going into optical emission from the jet is greater in lowluminosity quasars. This correlation between colour and luminosity may be of use in cosmological distance scale work.

This synchrotron model does not, however, fit ˜10% of the quasars, which have both red colours and high equivalent width emission lines.We hypothesise that these red, strong-lined quasars have intrinsically weak Big Blue Bumps.

There is no discontinuity in spectral properties between the BL Lac objects in our sample and the other quasars. BL Lac objects appear to be the red, low equivalent width tail of a continuous distribution. The synchrotron emission component only dominates the spectrum at longer wavelengths, so existing BL Lac surveys will be biased against high redshift objects. This will affect measurements of BL Lac evolution.

The blue PHFS quasars have significantly higher equivalent width C IV, Hβ and [O III] emission than a matched sample of optically selected QSOs.

As a pilot survey for the forthcoming 6dF Galaxy Redshift Survey, spectroscopy of galaxies selected in the 1.2 micron J waveband with the DENIS imaging survey was performed at the UKST using the FLAIR II multi-object spectroscope. Sixty-nine galaxy redshifts were obtained in a high galactic latitude field and an additional 12 redshifts in a low galactic latitude (b = 17˚), obscured field. This spectroscopic followup of NIR selected galaxies illustrates the feasibility of obtaining redshifts with optical spectra on galaxies selected at much longer wavelengths. It validated a very preliminary algorithm for star/galaxy separation for high galactic latitude DENIS objects, with 99% reliability for J <13.9. The FLAIR II redshifts are in excellent agreement with those, previously published, of 20 common galaxies. However, the FLAIR II redshift determinations presented here required substantially longer integration times to achieve 90% completeness than expected from previous optical surveys at comparable depth. This is mainly due to a degradation in overall fibre throughput due to known problems with ageing of the prism–cement–fibre interface with exposure to UV light. In comparison to our high galactic latitude field, our low latitude (high extinction) field required 2.5 times more exposure time for less than 50% of successful redshift measurements.

Among the J ≤ 13.9 galaxies with measured redshifts, only 376% display emission lines, in comparison with 60% of emission line galaxies in optical samples of comparable depth. These galaxies are, on average, half a magnitude bluer in B-J than galaxies of the same luminosity without emission lines. We confirm a previous optically-based result that the fraction of galaxies with emission lines increases rapidly with decreasing galaxy luminosity. The J band luminosity function is estimated. Our high latitude field displays a concentration of galaxies at cz ≲ 38 000 km s−1 suggesting a possible supercluster.A radial velocity is reported for a galaxy lying near the projected centre of the Abell 1434 cluster of galaxies, for which no cluster redshift is currently available.

The surface of the Sun is continually oscillating due to sound waves encroaching on it from the interior. Measurements of the surface velocity are used to infer some of the properties of the regions through which the sound waves have propagated. Traditionally, this has been done by using a modal decomposition of the surface disturbances. However, the use of ray descriptions, in the form of acoustic holography or time–distance helioseismology, provides an alternative approach which may reveal more detailed information about the properties of local phenomena such as sunspots and active regions. Fundamental to any such treatment is determining the correct ray paths in a given atmosphere. In the simplest approach, the ray paths are constructed to minimise the travel time between two points (Fermat's principle). However, such an approach is only valid in the high frequency limit, ω » ωc, N, where ωc is the acoustic cut-off and N the Brunt-VÄisÄlÄ frequency. Although ωc is often included in time– distance calculations, and N occasionally, the same is not true of acoustic holography. We argue that this raises concerns about image sharpness. As illustrations, representative ray paths are integrated in a realistic solar model to show that the Fermat approximation performs poorly for frequencies of helioseismic interest. We also briefly discuss the importance of the Brunt-VÄisÄlÄ frequency to the time–distance diagram.

Although the extra-solar planets discovered so far are of the giant, gaseous type, the increased sensitivity of future surveys will result in the discovery of lower mass planets. The detection of O2 in the atmosphere of a rocky extra-solar planet would be a potential indicator of life. In this paper we address the specific issue of whether we would be able to detect the O2 A-band absorption feature in the atmosphere of a planet similar to the Earth, if it were in orbit around a nearby star. Our method is empirical, in that we use observations of the Earth's O2 A-band, with a simple geometric modification for a transiting extra-solar planet, allowing for limb-darkening of the host star. We simulate the spectrum of the host star with the superposed O2 A-band absorption of the transiting planet, assuming a spectral resolution of ~8 kms−1(typical of current echelle spectrographs), for a range of spectral signal-to-noise ratios. The main result is that in principle we may be able to detect the O2 A-band of the transiting planet for host stars with radii R≤ 0.3Rʘ. However, using existing instrumentation and 8m telescopes, this requires target M-stars with m(V) ≈ 10 or brighter for integration times of ~10 hours or less. The number of such stars over the sky is small. Larger aperture telescopes and/or improved instrumentation efficiency would enable surveys of M-stars down to m(V) ≈ 13 and greatly improve the chances of discovering life elsewhere.

Here we present the first results of a search for new optical supernova remnant candidates and other filamentary objects on films produced by the Anglo-Australian Observatory/UK Schmidt Telescope Há Survey. Sixty-one fields, or 26% of the Galactic plane survey fields, have been visually examined. This has resulted in the detection of four newlarge diameter filamentary structures, and the discovery of extensive new optical emission in two previously known optical supernova remnant candidates.

Magnetohydrodynamic devices that can accelerate plasmas to speeds of the order of hundreds of kilometres per second have been designed and built for nearly forty years. Up to the time of writing, however, the theory for such devices has been exclusively non-relativistic. In this paper we derive the special relativistic magnetohydrodynamic (SRMHD) equations and use them to obtain the relativistic, magnetic nozzle equation which describes the production of jet flows with speeds approaching the speed of light.We obtain analytic solutions to this equation and show that, in principle, magnetic field gradients can accelerate a plasma to highly relativistic speeds. We also show that the exit kinetic energy, EK, of a particle is given by the equation EK = m0C2FR, where m0 is the rest mass of the particle and CFR is the fast magnetosonic speed at the start of the flow.

The relativistic nozzle differs in a number of ways from the non-relativistic case.A non-relativistic nozzle has a relatively symmetric converging/diverging shape, while a highly relativistic nozzle converges in the usual manner, but diverges, in an abrupt fashion, at the very end of the nozzle. The gentle divergence of non-relativistic nozzles causes the exit plasma densities and magnetic fields of the flow to have values that are small relative to their values at the start of the nozzle. The abrupt divergence of a highly relativistic nozzle implies that, for a less than perfect nozzle, the exit values of the mass density and the magnetic field strength are comparable to their initial values. This unexpected dichotomy in behaviour may have future application in understanding the ‘radio-loud’ and ‘radio-quiet’ relativistic jets that are produced from astrophysical sources.

Video recordings of images of binary stars at the focus of a 0.36m telescope have been used to select images recorded in instants of good seeing. The selected images have been analysed to give separations and position angles for the binary systems which are in good agreement with values predicted from previous observations. In these exploratory observations it has been shown that separations of 0.9 arcseconds can be measured with an accuracy of ~2% and position angles to ~1–2 degrees when the average seeing was ~1.3 arcseconds. These observations demonstrated that the diffraction limit of the telescope could be reached when the seeing was a factor of 2–3 greater than it. A binary with three magnitudes difference in the brightness of its components has been measured with comparable accuracy although difficulties are anticipated for binaries with components closer than ~2 arcseconds with this magnitude difference. The limiting magnitude is determined by the need to limit exposure times of individual frames to be comparable with or less than the atmospheric coherence time.

At 12:56 p.m., on Monday 21 July 1969 (AEST), six hundred million people witnessed Neil Armstrong's historic first steps on the Moon through television pictures transmitted to Earth from the lunar module, Eagle. Three tracking stations were receiving the signals simultaneously. They were the CSIRO's Parkes Radio Telescope, the Honeysuckle Creek tracking station near Canberra, and NASA's Goldstone station in California. During the first nine minutes of the broadcast, NASA alternated between the signals being received by the three stations. When they switched to the Parkes pictures, they were of such superior quality that NASA remained with them for the rest of the 2-hour moonwalk. The television pictures from Parkes were received under extremely trying and dangerous conditions. A violent squall struck the telescope on the day of the historic moonwalk. The telescope was buffeted by strong winds that swayed the support tower and threatened the integrity of the telescope structure. Fortunately, cool heads prevailed and as Aldrin activated the TV camera, the Moon rose into the field-of-view of the Parkes telescope. This report endeavours to explain the circumstances of the Parkes Observatory's support of the Apollo 11 mission, and how it came to be involved in the historic enterprise.

I would like to begin by saying what a pleasure it is for me to be here. For my entire adult life I have wanted to come to Australia. Actually, I have been invited to visit here twice before, but each time I was thwarted by circumstances beyond my control. But this time I was determined to (a) prove that the third time is indeed the charm, and (b) pay homage to Walter Stibbs, who in my mind is the epitome of a scholar and a gentleman. I have known Walter as colleague, teacher, and friend, not to mention as an inspiration, both professional and personal. So I am here today to try to give some sense of progress in the study of stellar atmospheres, a field that Walter has graced with his virtuosic touch. I will follow an unabashedly personal path, describing the development as I experienced it. I will focus almost entirely on early-type stars, where we may reasonably expect the atmospheric layers to be homogeneous, and in radiative equilibrium. Only at the end will I mention our nearest stellar neighbor, the Sun, which, because we can study it in so much detail, offers counterexamples to almost all of the the theory that works so well for early-type stars. I offer apologies in advance to anyone this approach may offend.

Robert Innes was one of a select band of amateur astronomers who made the transition to professional ranks towards the end of the nineteenth century. Initially he had a passion for mathematical astronomy, but after settling in Sydney he developed a taste for observational astronomy, specialising in the search for new double stars. He quickly became known for his success in this field and for his publications on solar system perturbations, and with John Tebbutt's patronage managed to secure a clerical position at the Royal Observatory, Cape of Good Hope. Once there he continued to observe in his spare time and to publish, and, with strong support from Sir David Gill, was appointed founding Director of the Transvaal Observatory. By the time he died in 1933, Innes had received an honorary D.Sc. from Leiden University, and had established an international reputation as a positional astronomer.This paper provides an interesting case study of a well-known ‘amateur-turned-professional’, and an example of the ways in which patronage played a key role in nineteenth and early twentieth century Australian and South African astronomy.