It was first shown by von Zeipel (1924) that strict radiative equilibrium is impossible in the radiative zones of a uniformly rotating star. This result lead Eddington (1925) and Vogt (1925) to independently suggest the existence of large-scale meridional currents in the radiative zones of rotating stars. Eddington argued that since these currents will transport angular momentum, the condition of strict radiative equilibrium would result in meridional currents combined with differential rotation.

The non-linear modal equations governing magnetoconvection in a fluid layer have been integrated forward in time incorporating a discrete spectrum of horizontal wave numbers, distributed within the range supporting convection. By progressively deleting some of the decaying modes and introducting additional modes within the range of growth it is possible to establish the evolution, or otherwise, of a preferred horizontal scale, which determines the horizontal cell size of the convective motions. Further, the influence of the magnetic field strength on cell extent can also be determined.

It is shown that for the eclipsing variable stars MP Mus and SV Cen a least squares fitting procedure is more accurate when a linear (intensity) rather than a logarithmic (magnitude) scale is used.

The optical spectra of the AM Herculis binaries are characterized by extremely complex emission lines whose profiles can be resolved into at least three components which are formed in different regions of the accretion stream leading from the companion star towards the magnetic white dwarf. We present a theoretical model which localizes the formation region of the broad emission line component and provides information regarding the structure of this emitting region. In our model the particle trajectories are integrated in a Roche potential and the volume between the white dwarf and the companion has been divided into two different regimes of motion. In one region the gas escapes from the secondary near the inner Lagrange point and is accelerated along a straight line towards the white dwarf. In the other region the magnetic field is strong enought to divert the gas out of the orbital plane and to channel it towards the white dwarfs surface. The model has been used to interpret radial velocity and velocity dispersion data from the AM Herculis system E1405-451.

We discuss the properties of cyclotron radiation from accretion shocks located above the atmospheres of magnetic white dwarfs taking into account the effects of field spread and density and temparture structure. The models which are an improvement on previous point source models are shown to have characteristics that are in better overall agreement with the properties of AM Herculis type systems. Our calculations of the polarization properties of large polar cap emission regions are used to discuss the recent null measurements of circular polarization in DQ Herculis type systems.

The polarization properties of cylindrical magnetic accretion columns are calculated allowing for electron scattering within the emission region. The results are used to estimate the effects of electron scattering and geometry on the observed properties of AM Herculis type systems.

X-ray data show that substantial quantities of hot gas are cooling near the centres of many clusters and groups of galaxies. The existence of such cooling flows has been challenged because of the lack of evidence for star formation from the cooled gas. Spectra of cooling flow galaxies show filling in of the continuum shortward of the break at 4000 Å relative to normal elliptical galaxies. This is consistent with some continuing star formation. Extended regions of line emission are commonly associated with cooling flows. If the initial-mass-function of the newly formed stars which affect the 4000 Å break is like that which applies in the solar neighbourhood, then these stars can also power the line emission. The strength of the 4000 Å break is shown to correlate with the Hβ flux in the manner expected when this is the case. This allows us to esimate the star formation rate from the line luminosity.

The rate of star formation required to account for the line emission still falls well short of the rate at which gas is inferred to be cooling. It is argued that, nevertheless, the cooling gas is probably forming into stars. The overall initial-mass-function must be different from that which applies in the solar neighbourhood, but this should not be surprising given the different ambient conditions in a cooling flow.

Hypervelocity impacts are considered to be the main mechanism for the production of craters on the surfaces of planets and moons. Two- and three-dimensional numerical simulations for the first few seconds of large-body impacts will be discussed. Both normal and oblique impacts will be considered, with particular emphasis being placed on the distribution of impact products.

Work is in progress on the extension of a detailed stellar structure code to explore a suggested solution to the Solar Neutrino Problem where the Sun has a small (∼0.01M⊙) high-Z core on entry to the ZAMS. A basic premise of such models is that the core will burn itself out by solar age and the model acquire a neutrino luminosity in line with that observed. The work to date has involved the construction of a standard solar model and, currently, the development of inhomogeneous models with associated adjustments to the structure equations.

It now appears almost certain that the precursor of SN 1987a was the brighter of the components of Sk-69 202, a blue supergiant, with a precursor mass of perhaps 12-16 solar masses. Prior to the explosion the precursor had a core mass of order six solar masses, and 0.1 to 0.2 solar masses of residual hydrogen envelope. The compact nature of this star can account for many of the odd features of the subsequent light curve and spectral evolution.

An analysis of the light curve and colour evolution shows four distinct epochs, which probably relate to the initial expansion of the fireball and the escape of shock-deposited thermal energy, the hydrogen-rich layers becoming optically thin, the exposure of the helium core, and the increasing transparency of the helium core.

The supernova appeared to be at its maximum on May 10, but is dimmer than a normal Type II because its light is apparently derived from recombinations and the radioactive decay of 56Ni to 56Co to 56Fe rather than by the thermal energy deposited by the passage of the shock.

A photometric survey of a central region of the LMC has been undertaken to obtain a magnitude and colour limited sample of bright asymptotic giant branch (AGB) stars; the stars were selected from V and Ic plates taken by the UK Schmidt Telescope Unit (UKSTU) at Coonabarabran. Infrared JHK photometry has been obtained for all the stars in the sample in order to determine bolometric magnitudes, and spectra have been obtained for most of the stars to obtain spectral types. Stars in the sample have bolometric magnitudes up to the AGB limit of Mbol ∼ – 7.1, and many of the stars show evidence for dredge-up of carbon and s-process elements during helium shell flashes. A bolometric luminosity function has been constructed and its behaviour is discussed in terms of possible mass loss scenarios.

We report spectroscopic and photometric observations of the new DQ Hercuis system 1H0542-407, recently discovered by us to be the optical counterpart of a HEAO-1 X-ray source. Medium resolution spectroscopy using the AAT in the region λ3930 to λ4960 conducted over consecutive nights shows radial velocity variations at periods of ∼ 1910 s, consistent with the white dwarf rotation period, and 5.7 h, in agreement with the orbital period derived from our EXOSAT observations. The K semi-amplitude velocities are ∼ 50 and 20 km s-1 respectively, leading to a mass function f(M) = 3.3 ± 0.6 × 10-3M⊙ and an orbital inclination close to 20°. The emission line profiles are characterized by simple Gaussians whose FWHM vary at the rotation period. A time series analysis of high resolution photometry conducted on the ANU 2.3 metre telescope reveals the presence of several periodicities, including the orbital sidebands. The dominant sideband (Vr − Vo) arises from X-rays reprocessed in a region corotating at the orbital frequency. A model is developed for 1H0542-407 which indicates that the accretion disk is disrupted at ∼5Rwd by the primary’s magnetic field. The short period velocity variations arise within the magnetosphere. A white dwarf magnetic field strength of < ∼ 3 MG is implied.

We present an overview of the survey for radio emission from active stars that has been in progress for the last six years using the observatories at Fleurs, Molonglo, Parkes and Tidbinbilla. The role of complementary optical observations at the Anglo-Australian Observatory, Mount Burnett, Mount Stromlo and Siding Spring Observatories and Mount Tamborine are also outlined. We describe the different types of star that have been included in our survey and discuss some of the problems in making the radio observations.

Gamma-ray astronomy has traditionally been a difficult field of research due to the low fluxes from astronomical objects and the inherently poor angular response of detectors. Progress made in the field in the last twenty years is reviewed. Many major astrophysical problems can only be addressed with the future operation of more sensitive satellite experiments. Recent gamma-ray observations of the supernova SN1987 a are briefly discussed.

In γ-ray astronomy one often wishes to search for a periodic signal from a suspected point source. Either one knows the period in advance, for example in the case of a radio pulsar, or at least a range of possible periods, or one has no information and is searching “blind”, as in the case of SN1987a, unidentified sources in the COS-B catalogue, or binary X-ray sources without known pulse periods. In both cases one should adopt a strategy which give the best chance of obtaining a statistically significant result. The power of tests using the family of statistics based on the Rayleigh statistic is discussed for two extreme forms of possible light curves: a uniform distribution plus a delta function, and a cartoid distribution. Strategies for using these statistics are discussed. Methods of obtaining confidence bands, and in the case of an unsuccessful search, upper-limits to any pulsed component are described, and graphs given which enable these to be calculated readily given the value of the statistic obtained.

The Lyman mission will undertake the first sensitive high resolution spectroscopic observations in the largely unexplored 912-1216Å region. This astrophysically critical wavelength interval is exceedingly rich in diagnostic spectral lines such as the Lyman series of atomic hydrogen and deuterium, the Lyman and Werner bands of molecular hydrogen and deuterium, and the resonance lines of numerous important species including CIII, NI-III and OVI. Lyman will have a major impact in all areas of modern astrophysics, with the most fundamental contribution being the determination of light element abundances in the local interstellar medium and in the intergalactic medium at low redshift. The mapping of hot gas (T ∼ 3 × 105K) and molecular hydrogen and HD in the disk and halo of our galaxy represent additional major objectives for which Lyman is uniquely qualified.

The Lyman payload will comprise a grazing incidence telescope and three spectroscopic instruments: the prime spectrograph operating between 912-1250Å with a resolution of λ/ Δλ ∼ 30,000, a far ultraviolet spectrograph (1200-2000Å;λ/ Δλ ∼ 10,000), and an extreme ultraviolet spectrograph (100-900Å; λ /Δλ ∼ 300). Observations will be conducted from a highly efficient 48 hour elliptical orbit which will allow long un-interrupted exposures and real time operations. It is anticipated that Lyman will be launched by Ariane in 1996, and will have an operational lifetime of at least 5 years. Data reception and spacecraft control will be undertaken from ground stations in Spain and in Australia.

Lyman is currently being studied at Phase-A level by Australia in close coordination with the European Space Agency. The scientific involvement is the responsibility of the Lyman Science Working Group, composed of members representing the various astronomical institutions in Australia. Funding to support the technical and scientific aspects of the mission is provided via the Australian Space Board and the Department of Industry, Technology and Commerce in recognition of the major opportunity that Lyman presents to the Australian aerospace industry.

A cloud with a l.s.r. velocity of ∼ 160 km s-1 and a half-width of ∼ 25 km s-1 was mapped in the (1,1), (2,2) and (4,4) lines of para NH3 and the (3,3) and (6,6) lines of ortho NH3 using the 40″ arc beam of the 100-m Effelsberg telescope. The cloud was extended some 5′ in latitude and contained a central concentration ∼ 1′.5 in size at ℓ = 1°.59; b=0°.01. Line temperatures of the four higher transitions define a rotational temperature of ∼ 120 K, while the (1,1) and (2,2) alone yield the lower value of ∼ 40 K. The high temperatures, well above that of the dust, are too high to be caused by collisions with H2 molecules in the ground state, but might result from collisions with H2 in excited states. On a (ℓ, v) plot the cloud does not coincide with any generally accepted galactic centre feature but it is possibly located near the periphery of the ‘rotating nuclear disk’, where conditions would be favourable for the production of shocks, excited H2 and possibly high NH3 temperatures.

The Parkes 64-m antenna has been used to map ammonia emission in the (J,K = 1,1) and (J,K = 2,2) transitions toward molecular cloud complex NGC 6334. This complex contains a number of OH and H2O masers, HII regions and IR sources, and is a rich source of molecular line emission.

Distributions of observed and derived quantities are presented with a linear resolution of ∼ 1 pc. Velocity anomalies are present near the two OH masers NGC 6334A and B, and the source of ammonia emission located near the northernmost H2O maser is one of the most intense sources of NH3 emission in the Galaxy.

Observations have been made, using the Epping 4-m radio telescope, of emission from the J = 1-0 transition of CO (115 GHz) towards the Southern Coalsack. The half-power beam-width was 2′.7 arc and the radial velocity resolution was 0.07 km s−1. The line was found to be distributed with varying intensity over an area of 63′ × 36′ arc. The mean radial velocity was −5.8 km s−1 and mean half-intensity linewidth 1.18 km s-1. A typical line temperature was 8 K with maxima exceeding 12 K. The results suggest a stable dark cloud region with no significant evidence of systematic motions.

The design and scientific applications of a 96-channel filter spectrograph of 1 MHz resolution are presented. The spectrograph is currently under construction and will be installed on the Parkes telescope in 1987-1988. Its main scientific objective is dynamic spectral studies of decimetre- and metre-wavelength bursts from flare stars. However, it will also be used for performing large-scale pulsar surveys, and dynamic spectral observations of interplanetary scintillation of compact sources, interstellar scintillation of compact extragalactic sources, and interesting radio sources in general.

We show that plasma emission generated in the coronae of flare stars should be detectable at metre- and decimetre-wavelengths. We plan to search for fundamental and second-harmonic plasma radiation by observing in two harmonically related bands, 200 to 250 MHz and 400 to 500 MHz. With noise-adding to stabilize receiver gain, the sensitivity (3σ) of each channel of the spectrograph is ∼ 1.5 Jy for a 1-s integration. Previous studies have reported peak flux densities of up to ∼ 35 Jy and ∼ 12 Jy at 240 MHz and 410 MHz respectively for radio bursts from flare stars.