UBV observations of the massive binary system TT Aur were carried out mainly at theTurkish National Observatory (TUG). These observations, together with IUE spectra and times of eclipse minima collected from the literature, were used to study the system parameters.

Simultaneous solution of the light curves by the Wilson-Devinney code allows a semi-detached configuration with a slightly larger Roche-lobe filling secondary. This picture is supported by other evidence. The shoulders of the primary minimum suggest some excess absorption, in keeping with circumstellar material in the form of a disk-like structure around the primary component. The deeper primary minimum in the U filter may indicate a hotter region on the secondary-facing hemisphere of the primary.

The period variation of the system can also be related to the possible existence of a third component in a circular orbit around the system.

An alternative detached representation is also considered using optimal curve-fitting techniques. We appeal for further observations to help resolve some outstanding issues in this interesting massive binary.

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.

We have combined the observational data of the AAO/UKST and Marseille Hα surveys to extract preliminary new results about ionised structures of our Galaxy. This includes the detection of a new large bubble located in the far part of the Carina arm.

A test of the hypothesis that flares derive their energy from large scale current systems inferred from active region vector magnetograms is proposed. The test involves a statistical comparison of the flarerelated change in coronal magnetic energy (based on the magnetohydrodynamic virial theorem) and an independent measure of the energy of the flare. A simulation suggests that — assuming the hypothesis is correct—the test requires around 50 flares with energy greater than 5×1023 J to return a significant result. Existing archives of vector magnetograms should provide sufficient data for such a study.

We present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325·5° ≤l ≤ 333·5°; −0·5° ≤ b ≤ 3·5°) were completed in December 1998. Single-dish observations of the full survey region (253° ≤ l ≤ 358 ° |b| ≤ 1°) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS H I data, with particular attention to the smallest-and largest-scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent H I shells. On the small scale, we note extremely compact, cold clouds seen in H I self-absorption. We explore how these two classes of objects probe opposite ends of the H I spatial power spectrum.

Beam-driven Langmuir waves in the solar wind are generated just above the electron plasma frequency, which fluctuates in the inhomogeneous solar wind plasma. Consequently, propagating Langmuir waves encounter regions in which the wave frequency is less than the local plasma frequency, where they can be reflected, mode converted to transverse electromagnetic waves, and trapped in density wells. The aim here is to investigate Langmuir wave reflection and mode conversion at a linear density gradient for typical solar wind parameters. It is shown that higher mode conversion efficiencies are possible than previously calculated, but that mode conversion occurs in a smaller region of parameter space. In addition, the possibility of detecting mode conversion with in situ spacecraft Langmuir wave observations is discussed.

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.

Over the past few years, site-testing at the South Pole has revealed conditions that are uniquely favourable for infrared astronomy. In particular, the exceptionally low sky brightness throughout the near and mid-infrared leads to the possibility of a modest-sized telescope achieving comparable sensitivity to that of existing 8–10 metre class telescopes. An 8 metre Antarctic telescope, if constructed, would yield performance that would be unrivalled until the advent of the NGST. In this paper we review the scientific potential of infrared telescopes in Antarctica, and discuss their complementarity with existing 8–10 metre class telescopes and future proposed space telescopes. In particular, we discuss the role that a 2 metre class infrared telescope plays in future plans for the development of an observatory on the Antarctic plateau.

We have measured the rotational velocity of the companion star to be Ʊrot sin i= 80 ± 10 km s ˗1 (1σ) by fitting Kurucz model spectra to our observed spectrum of the black-hole candidate GRO J1655–40. From this we have calculated q = 0·31 ± 0·08, the mass of the compact object to be M1 = 7·91 ± 3·79 Mô (1σ) and for the companion starM2 = 2·76 ± 1·79 Mô (1σ), which is consistent with previous studies. We have also determined Teff = 6500 ± 50 K and [Fe/H] = −0·15 +0·15-0·10.

Observations of the Einstein Cross QSO reveal that the mid-infrared region is unaffected by microlensing. Thus, the infrared emission region must be extended on a scale >1017 cm, ruling out synchrotron models, but consistent with dust emission models. Other constraints rule out starburst models. The flux ratios greatly constrain the lens model.

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.

We review the theory of shock drift acceleration, developing the theory in detail for gyrophaseaveraged particles. It is shown howboth the upstream and downstream velocity spaces separate into different regions according to the interaction of the particles with the shock (reflection, transmission, head-on, overtaking). The effects of the cross-shock electric field and of the magnetic overshoot are discussed. The effectiveness of acceleration is estimated for Maxwellian and power law distributions. The condition for a beam instability to be generated by reflected particles is determined and found to be independent of the distribution function for isotropic inflowing electrons.

PSR B1259 – 63 is a 47 ms radio pulsar with a high spin-down luminosity which is in a close, highly eccentric 3·5 yr orbit about a bright stellar companion. The binary system may be a detectable source of hard ã γ-rays produced by inverse Compton scattering of photons from the B2e star SS2883 by electrons and positrons in the pulsar wind. The star provides an enormous density of optical photons in the vicinity of the pulsar, particularly at epochs near periastron. We calculate the emission from the unshocked region of the pulsar wind, assuming that it terminates at a shock where it attains pressure balance with the companion’s wind. The spectra and light curves for the inverse Compton emission from the shock-terminated wind are compared with those for an unterminated wind. If the pulsar’s wind is weaker than that from the companion star, the termination of the wind decreases the inverse Compton flux, particularly near periastron. The termination shock geometry has the effect of decreasing the asymmetry of the γ-ray light curve around periastron, which arises because of the asymmetrical variation of the scattering angle.

We present evidence for an anti-correlation between faint QSOs and B < 23 galaxies.A sample of 192 QSOs in a 2.5 deg2 area has been imaged using the Isaac Newton Telescope Wide-Field Camera. The cross-correlation signal is of a similar amplitude to the galaxy auto-correlation function at the limit of B < 23, but is negative in sign. As fainter galaxies are selected the negative correlation signal becomes less significant, until the signal is effectively zero at B < 26. We propose two alternate explanations for the observed effect. The first is gravitational lensing of the faint background QSOs, which have a flat number count slope. However, the lensing signal is significantly higher than expected in conventional models. The second possibility is that inter-galactic dust absorption is responsible. A reddening of only E(B - V) ≃ 0.02 is required to produce the observed correlation. The large 2dF and SDSS QSO surveys should allow a definitive solution to the question of QSO–galaxy correlations.

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.

The effects of charged dust on the steepening of the fields in nonlinear Alfvén waves in astrophysical weakly ionised plasmas are investigated. It is found that the formation of current singularities in the wave due to nonlinear ambipolar diffusion is strongly modified by the effects of the dust. The basic modes for propagation along the magnetic field in a dusty plasma are highly dispersive and split by the anisotropy of the magnetic field into two modes that are oppositely circularly polarised rather than linearly polarised. The right hand circularly polarised wave experiences a cutoff due to the presence of the dust. We derive nonlinear fluid equations describing the dusty plasma, and make approximations for strong coupling of the dust to the neutrals, and for stationary dust. Numerical solution of the equations shows that a nonlinear wave with sharp current features due to ambipolar diffusion involves a rotation of the wave magnetic field about the direction of propagation, and an oscillation of the field components, due to the mode splitting effects of the dust. This is in contrast to the dust-free case, where the sharp reversal of the transverse magnetic field component occurs in a single plane.

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 have commenced a program to monitor the gravitational lens B1152+199 with the Australia Telescope Compact Array (ATCA) to search for variability of the lensed components with the goal of measuring the lensing time delay. As part of this program we made a 9 hour full-synthesis observation in June 2000 to derive a ‘template’ for model-fitting the shorter, multi-epoch, monitoring observations. We report here on the results of this full-synthesis observation and on three additional epochs of monitoring for time variation.

Digital signal processing is one of many valuable tools for suppressing unwanted signals or inter-ference. Building hardware processing engines seems to be the way to best implement some classes of interference suppression but is, unfortunately, expensive and time-consuming, especially if several miti-gation techniques need to be compared. Simulations can be useful, but are not a substitute for real data. CSIRO’s Australia Telescope National Facility has recently commenced a ‘software radio telescope’ project designed to fill the gap between dedicated hardware processors and pure simulation. In this approach, real telescope data are recorded coherently, then processed offline. This paper summarises the current contents of a freely available database of base band recorded data that can be used to experiment with signal processing solutions. It includes data from the following systems: single dish, multi-feed receiver; single dish with reference antenna; and an array of six 22 m antennas with and without a reference antenna. Astronomical sources such as OH masers, pulsars and continuum sources subject to interfering signals were recorded. The interfering signals include signals from the US Global Positioning System (GPS) and its Russian equivalent (GLONASS), television, microwave links, a low-Earth-orbit satellite, various other transmitters, and signals leaking from local telescope systems with fast clocks. The data are available on compact disk, allowing use in general purpose computers or as input to laboratory hardware prototypes.

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.