An accretion disc becomes warped when subjected to a torque which is misaligned with the disc plane. Such torques may be caused by Lense-Thirring precession near a spinning compact object, or the quadrupole field of a binary star. Here the flow in an adiabatic warped disc is modelled as a two-dimensional shear layer with linear velocity profile and free surface boundary conditions, and is investigated by means of a linear stability analysis.

The flow is found to be unstable whenever it contains a critical layer, i.e., a level at which the shear velocity is equal to the phase velocity. The instability occurs over a broad wavenumber range and has a typical dimensionless growth rate ≈ 0.1 for both the compressible and incompressible cases. These waves grow with a time-scale of about one orbital period, and are likely to have a major effect on the disc viscosity.

Evidence has been mounting for some years that cosmic rays have a dwell time in the disk of the Galaxy of 106-107 years. This evidence comes mainly from the study of the chemical composition of the cosmic rays, for if the particles were stored in the Galaxy for a longer time the heavy nuclei would suffer more collisions with interstellar matter and would be broken down into lighter nuclei or protons (see, for example, Shapiro).

Time variations in both the NGC 6334 and Orion OH sources have been reported by the Berkeley group. The variations in NGC 6334 have been partially confirmed by the group at the Lincoln Laboratory, who show that the variations are confined to the southern source, NGC 6334B. These latter authors find variable components at —6.6 and —7.9 km/s at 1665 MHz and at —8.9 km/s at 1667 MHz. Both features at 1665 MHz appear to vary, both up and down, with time; during 1966 October the characteristic rise time was nine days or less. The Berkeley results show that the linear polarization was constant during a two-week period in 1965 October. The Lincoln Laboratory results from 1966 October to 1967 June show that both the degree and sense of circular polarization remain constant as the three features vary with time.

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.

In this paper we study the steady-state interplanetary propagation of solar cosmic-rays by means of analytic solutions of the equation of transport. The cosmic-rays are released monoenergetically from a fixed heliocentric radius and redistribute in energy as they propagate. Previous investigations by Goldstein et al. (1970), Urch and Gleeson (1971,1972), and Parker (1965, 1966), were either not general enough or used numerical solutions which could not deal with strictly monoenergetic initial injection nor maintain accuracy over a wide range of particle energies. We use the analytic solutions of Gleeson and Webb (1973) and show the energy changes, the redistribution in energy (or momentum) and the characteristics of the particle flow or streaming.

The origin of the high degree of linear or circular polarization frequently observed in the 18 cm radiation of hydroxyl molecules has proved to be a formidable theoretical problem for which no adequate solution appears to exist at present. It is usually supposed that the radiation arises from some form of maser action and so it is possible that the polarization may arise from an interaction of radiation with the various frequencies and polarizations, through the coupling agency of the populations of the energy levels of the molecule.

The recent upgrading of the Tidbinbilla two-element interferometer to simultaneous S-band (2.3 GHz) and X-band (8.4 GHz) operation has provided a powerful new astronomical facility for weak radio source measurement in the Southern Hemisphere. The new X-band system has a minimum fringe spacing of 38 arcsec, and about the same positional measurement capability (approximately 2 arcsec) and sensitivity (1 s rms noise of 10 mJy) as the previous S-band system. However, the far lower confusion limit will allow detection and accurate positional measurements for sources as weak as a few millijanskys. This capability will be invaluable for observations of radio stars, X-ray sources and other weak, compact radio sources.

Three mirrors of the White Cliffs Solar Power Station are currently being used for very high energy γ-ray Astronomy while the University of Adelaide very high energy γ-ray telescope is being designed. Use is made of fast-timing to obtain γ-ray arrival directions to an accuracy approaching 1 °. The experimental arrangement and operation of the telescope is described and our current observing program is outlined.

Recent observations of the Centaurus region by Harries et al., Chodil et al., and Cooke et al. have firmly established the existence of a variable X-ray source, Centaurus XR-2. This source is unique in that its variability has been established beyond doubt.

It is shown that real-time FFT techniques used in conjunction with a small telescope can yield useful sensitivity. The suitability of the Crab pulsar as a calibrator is assessed. The mains frequency modulation in the night sky above Perth is clearly discerned, with several harmonics. Detectable signal modulation limits for SN 1987A are derived as a function of frequency in the range 10-2000 Hz.

The possibility of the occultation by Neptune of a star of similar apparent magnitude to itself was first pointed out by the amateur astronomer Ross A. Shuart. It was clear that such an event would provide data on Neptune’s position which would be of value to the observatories which produce the planetary ephemerides. The existing ephemeris of Neptune is known to contain small errors which have been accumulating over many years.

Linear stability theory for Rayleigh-Benard convection shows that for a specified Rayleigh number, greater than some critical value, only a finite range of horizontal wave numbers support convective instability in a horizontal layer of fluid heated from below. However, it is not possible to predict the preferred horizontal scale of established motions from this approach although it is clear from observations, particularly of the solar surface, that a preferred cell size does prevail. In an endeavour to establish a preferred horizontal scale appropriate non-linear modal equations have been integrated forward in time, initially incorporating a discrete band of wave numbers equally spaced across the range that supports convection, for a specific Rayleigh number. The horizontal resolution was improved in subsequent integrations by first deleting modes that had substantially decayed and then introducing new modes on a finer horizontal mesh in the vicinity of what appeared to be the evolutionary dominant mode. Finally, the multimode integrations were continued in time until the evolution of a dominant horizontal mode from within the restricted range was evident. Both the model characteristics and numerical scheme adopted placed limits on the degree of horizontal refinement that could be undertaken with confidence.

A photon with frequency in the range v to v + dv travelling in a direction n̂ within the solid angle dΩ is written (v, n̂).

Considering a mass of gas which is stationary relative to an observer and whose atoms are in continuous random thermal motion, then a redistribution function

A Millimetre-wave Astronomy Workshop was held at the CSIRO Radiophysics Laboratory in Marsfield, Sydney, on 19 April 1995. The workshop, sponsored by the Australia Telescope National Facility (ATNF), was a meeting of mm-wave specialists as well as astronomers and students interested in the field, and attracted about 80 participants from 13 institutions. The program consisted of 23 oral contributions (5–45 min) followed by lively discussions. Abstracts of most of the contributions are presented here, arranged by groups dealing with subjects such as ‘A Basic Introduction’, ‘Astronomy in the mm-range with Mopra’ and ‘Projects: Galactic and Extragalactic 3 mm-wave astronomy’.

Reported data on the Chandlerian nutation show that there are irregular yet related changes in the rate of energy gain, the damping and the phase, changes which were remarkably great in the late 1920s. Dynamical interpretations need a model that has friction elements as well as springs and dashpots; it then offers further applications as well; e.g. to a correlation between reported values of the Love number k and tidal potentials. The model is used in discussing the increases in amplitude and the advances in phase; the short and long-term rates of energy gain and their interruptions and damping; the correlation between short Chandlerian periods and large amplitudes in the annual nutation; and the correlation between damping and the apparent frequency. Doubts are expressed about nutational values of Q. A geophysical interpretation of the model is obtained from seismic data. It was found that every large rise in the nutational energy was preceded by an earthquake in the Andes region; and that the secular rate of energy gain varied with the circum-Pacific seismicity. Decreases in these were accompanied by rises in the Earth’s rotational acceleration and were followed by deep earthquakes in a diminishing region east of the Andes. It appears that the nutational and seismic events are due to tectonic stress, and intermittently this is relieved by subduction.

The Parkes 64-m radio telescope equipped with a 3 GHz maser on loan from the Onsala Space Observatory has been used to observe the three ground-state transitions of CH (at 3264, 3335 and 3349 MHz) towards a total of 74 HII regions, mostly at southern declinations. In this paper the regions and related characteristics are listed, and the CH spectra displayed.

A number of authors (Reddish, 1968, 1969, Reddish and Wickramasinghe 1969) have stressed the importance for star formation of the role of condensation of H2, onto solid grains inside the cool dark regions of a large interstellar cloud. However, although the thermodynamic consequences of the existence of grains have been extensively studied, the dynamical implications have received little attention. Solid grains of course do not possess a thermal pressure as their gaseous counterpart does, neither do they directly experience the magnetic fields which thread the ions and electrons of the gas cloud. The grains therefore, as soon as they are formed, are free to fall toward their common centre of mass, relatively unrestricted by the constraints on the gas cloud.

Until the last six years few infrared observations of astronomical objects (other than the Sun and planets) had been attempted. Those few were primarily concerned with obtaining bolometric corrections and effective temperatures, the variation of bolometric magnitudes of late-type variables, and the derivation of the laws of interstellar extinction.