These observations have been made with the 210ft-60ft variable baseline interferometer at the Australian National Radio Astronomy Observatory.

In variable star work, the frequent observations of comparison stars during a night often clearly indicate the presence of either changes in extinction or changes of zero point of the photometric system, or both effects simultaneously. In a magnitude — air mass plot, the graph is not linear, but is usually a loop. These loops are well known to observers but so far very little has been published about this problem. Young’s (1974) chapters are perhaps the only exception.

In this talk I shall describe briefly some of the theoretical ideas of the origin of the Magellanic Stream and then give a more personal view of the results of model fitting.

The Magellanic Stream definitely seems to be an extragalactic feature: the apparent connection of the Stream to the Magellanic Clouds and the continuity of the radial velocity profiles make it highly implausible that the Stream is a local foreground feature.

In comparison with all other branches of astronomy, X-ray astronomy suffers from a relative dearth of image forming devices. No X-ray lens is known and image formation by reflection requires glancing incidence optics which have small fields of view and are extremely difficult to fabricate, even for the small apertures (about 2 cm2) now employed. The only other imaging device which has been successfully employed is the simplest of all, the pinhole camera. Pinhole cameras with resolutions better than 10−3 rad are easily constructed, but the apertures are very small—not greater than about 10−4 cm2. The new instrument described here is closely related to the pinhole camera and may be viewed as an attempt to overcome the aperture restrictions of this simple device.

Simple hydrostatic equilibrium models have been very successful at describing the physical conditions in hot coronal loops (T > 106 K). However, equilibrium models of cooler loops predict densities that are much lower than observed. We follow the evolution of a hot loop which undergoes a sudden reduction in heat input. The physical conditions in the cooling loop show significant departures from equilibrium. Such models appear to be able to reproduce the physical conditions observed in intermediate temperature loops (105 < T < 106 K).

In this paper we report that the available data on the measured pulsed fraction of X-rays from the Crab Nebula between the energies 0.7 and 300 keV indicate that it is no longer necessary to postulate an intrinsic change in the pulsar spectral index near 30 keV. Furthermore the spectral flattening which is evident at low energies can be entirely attributed, within the precision of the available statistics to the destruction of time coherence of the pulse structure by the scattering action of interstellar dust grains.

Solar X-ray bursts have been observed by a xenon-methane filled proportional counter on the satellite IMP-F. The counter is one inch deep and has a 14 mg/cm2 beryllium window. A slat collimator restricts the field of view to a full width of 5° in the direction of the satellite spin while allowing the counter to see ±60° in the plane containing the spin axis. The effective window area of the counter is 2.2 cm2, after allowing for the collimator.

The appearance of SN 1987A led to the implementation of a fast sampling option in the data collection system of the photometer on the University of Tasmania’s optical telescope. This option permits acquisition of continuous data trains of over one hour’s duration at sample rates of 5 kHz. Monitoring of SN 1987 A at regular intervals has permitted upper limits to be assigned to any pulsed fraction of the optical flux. Successful test observations of the Crab pulsar have been obtained, as well as observations of the geostationary Aussat satellites during their bi-annual specular-reflection episodes. For the latter, very accurate spin rates (∼1 Hz) are determinable in short data runs because of the higher frequency components (∼100 Hz) in their light curves. These components are produced by the rows of solar cells on the outer surfaces of the satellites, and fast-Fourier transform analyses essentially permit the numbers of rows of cells to be counted precisely.

It is well known from linear theory that a magnetic field or rotation, acting separately, have an inhibiting effect on the onset of thermal convection. This has been confirmed by corresponding studies of finite amplitude convection. On the other hand, when both magnetic field and rotation act together, the linear theory predicts that they may have conflicting tendencies. It is the purpose of the present paper to report on the investigation of these effects in the case of non-linear thermal convection.

The detection of non-radial oscillations on late-type dwarf stars may require the measurement of Doppler shifts of order 10 cm s−1. We report observations using the coudé echelle spectrograph of the 3.9 m Anglo-Australian Telescope which reveal a noise level in a 1 minute integration about a factor of one hundred greater than this. We then discuss a method of imposing a set of stable reference features on stellar spectra to permit Doppler measurements of the required accuracy. The method exploits a voltage-tuned solid Fabry-Perot interferometer whose passbands are fixed by a servo-control system to the light from a HeNe laser whose frequency is polarization-stablized. The desired wavelength stability demands careful control of the voltage, temperature and tilt of the etalon.

An accurate determination of the global Hubble Constant needs distance to objects well outside the Local Supercluster with redshift greater than ~ 2000 km/s. This is mainly to reduce the effect of the peculiar motion of the Local Group on the measured redshifts as well as to get away from the gravitational influence of the nearby high density regions.

The present practice of deriving distances involves identifying objects such as Cepheids and brightest red stars both in the Local Group galaxies as well as in the distant galaxies. This method cannot be used for galaxies at the large distances.

Current evolutionary theory indicates that evolving stars in globular clusters arrive on the horizontal branch with ~30% less mass than they had on the main sequence. If, as seems likely, this mass loss results from the outflow of unprocessed material at the stellar surface during the giant stage, and if the ejected mass were retained within the cluster between successive sweeps through the galactic plane (~108 yr), sufficient hydrogen (100-2000 M ⊙ should accumulate for detection. Radio searches, however, have failed to find evidence for either neutral or ionized gas. The hydrogen mass upper limits obtained by various workers are: Hills and Klein (1973) ionized H, 3.8 cm, <20-200 M ⊙; Knapp, Rose and Kerr (1973) neutral H, 21 cm, <1-20 M ⊙; Conklin and Kimble (1974) neutral H, 21 cm, <0.7-1.4 M ⊙.

We have extended the search into the optical region and have also calculated time-independent gas flow models to try to resolve this anomaly.

NGC 5236 is the fourth galaxy beyond the local group to be investigated at Parkes. Most of the observations were made with a single-channel 21 cm line receiver, coupled to the 210 ft dish. The half-power beamwidth is 13´.5. Declination scans were made through the galaxy, and treated by methods already established for NGC 551, NGC 3002 and NGC 31093. The peak antenna temperature is 1.5°K.

A fully-steerable 3.7 metre radiotelescope has been developed as an aid to undergraduate teaching. By using commercially available domestic satellite television components, excellent performance can be achieved at very low cost. The telescope is to be fully computer controlled, and has interchangeable feed horns and low-noise amplifiers for 21 cm, 2.5 cm and 7.5 cm. Experiments will include measurement of the surface temperature of the moon and Venus and of the effective temperature of the sun, plus observation of the brightest thermal and non-thermal galactic sources.

Australian astronomers have a proud history of comet-discovery, beginning with Rumker of Parramatta Observatory in 1824 (Baracchi 1914), and culminating with the outstanding achievements of Bill Bradfield of Adelaide. In the intervening one hundred and fifty years there have been a number of other notable comet-hunters and comet-observers, the most successful being John Tebbutt (see Orchiston 1981, 1982a, 1982b), Walter Gale, David Ross, and J. F. Skjellerup. Comets discovered by these Australian astronomers, and others, are listed in Marsden’s 1982 Catalogue of Cometary Orbits.

Model predictions of light changes due to non-radial stellar pulsation have been compared with the observations of light and colour changes in mid-B star variables made by Waelkens and Rufener (1985). It is concluded that these observations are consistent with the presence of low l (dipole and quadrupole) non-radial pulsations in the stars. This strengthens Waelkens and Rufener’s hypothesis that these variables may be identified with the 53 Persei stars. The differences between the model predictions for these large Q variables, which have periods in the 1 to 3 day range, and the predictions of small Q models, which apply to β Cephei variables, are explained.

The stability of accretion shocks in magnetic white dwarfs is investigated. Shock oscillations are simulated numerically, and in the simulations bremsstrahlung and cyclotron cooling are considered in an explicit form. We have found that for shocks with magnetic fields lower than 10 MG, shock oscillations can be sustained; while for magnetic fields greater than 20 MG, the oscillations are suppressed.