The resistive tearing mode instability is a mechanism that in some cases will render unstable a magnetohydrodynamic equilibrium of a plasma that is ideally stable, i.e. stable if no dissipative oiesses are taken into account. There is much experimental evidence that this instability is the cause of the current disruptions observed in laboratory plasma devices (von Goeler et al. 1974). In the astrophysical context, the instability has been invoked in connection with the solar flare energy release mechanism (Coppi and Friedland 1971) and the problem of the disconnection of the protostar matter from the interstellar magnetic field during star formation (Mestel 1966). In the latter problem the tearing instability gives rise to a much smaller timescale for magnetic reconnection than does ordinary resistive diffusion.

The Astronomical Society of Australia was formally constituted at an Inaugural Meeting held at 2 p.m. on Wednesday, 30th November, 1966, in the Grounds of the University of Sydney.

One of the critical parameters for a theory of emission from QSOs is the time scale of the variations in this emission. For many sources, changes occur faster than the light travel time across the source disk size as determined by VLBI observations. If the decimetre flux density is assumed to come from a small core, appropriate to the time scale of its variations then the brightness temperature must be far greater than ~ 1012 K allowed by the incoherent synchrotron process. These difficulties have been examined (Jones and Burbidge 1973; Burbidge and Stein 1975) using the QSO 2251 + 158 (3C454.3) as an example against which to test the theory. In this paper, I examine the time scale of the variations in 46 sources and show that most of these vary significantly within 2 years. The most rapid changes are in the QSOs 0736 + 017 and 1504–166 which have changed 40% within a few months — an order of magnitude faster than 2251 + 158.

A major area of difficulty in the cosmogony of the solar system is understanding how a large number of small planetesimals, which have condensed from the primordial gas, can aggregate into the ordered planetary system present today. Theories involving aggregation within a gaseous disc [e.g. Cameron (1973)] suffer the common difficulty that the particles, once condensed, are no longer supported by the radial gas pressure gradient and spiral rapidly in towards the Sun. Most of the planetesimals are dragged in to the central body in times several orders of magnitude less than would be required for larger bodies to accrete (Goldreich & Ward 1973).

After 21 years the Parkes radio telescope has undergone a major refit. A new VAX-11/750 running VMS has replaced the aged Digital Equipment Corporation PDP-9 computer. Other new equipment includes two systems not previously available — the Mk II RING communication system (Willing and Abies 1983) and the ‘observer workstations’.

A number of strong radio sources have been examined for structure with the 3’.5 beam of the 80 MHz radioheliograph at the CSIRO Solar Observatory, Culgoora Contour maps of brightness distribution are presented here for the galactic source W44, and the extra-galactic sources Fornax A, Pictor A and 3C353; they are compared, where possible, with maps at other frequencies.

Four examples of dwarf galaxies apparently undergoing mass loss are discussed. All have an Hα morphology suggesting a minor axis flow. This is supported by velocity field measurements in three cases. All also have at least one compact central object, probably a young star cluster, apparently powering the flow. Some implications of these results are briefly discussed.

Cyclotron lines have been observed in the X-ray spectra of two pulsed sources: Her X-1 (Trümper et al. 1978) and 4U 0115 + 63 (Wheaton et al. 1979). The generally accepted model for these objects involves an accretion flow from a companion star in a close binary system onto small regions close to the magnetic poles of a strongly magnetized neutron star. Immediately above the surface, matter is confined in an accretion column by the magnetic field.

In the terrestrial environment the abundance ratio of 18O to the common oxygen isotope 16O is about 1 in 490. Measurements of hydroxyl absorption in the interstellar medium show that 18OH as well as 16OH can be detected towards Sgr A and Sgr B2 (Gardner et al. 1970; Wilson and Barrett 1970; Williams and Gardner 1981); in these two galactic centre regions the 18OH isotopic species has an abundance relative to 16OH of about 1 in 220, somewhat greater than the terrestrial ratio of 18O to 16O.

Roche (1850) made the first study of the stability of binary systems. The problem he studied, and which now bears his name, is concerned with the stability of a liquid star in a synchronous, circular orbit about a point mass. Roche’s calculations predicted that if the separation between the liquid star and the point mass is S2.5rs’/3, where r is the unperturbed radius of the liquid star and s the ratio of the mass of the point to the mass of the liquid star, then the liquid star would be unstable. This result was generalised to two liquid stars orbiting each other by Darwin (1910, p. 436). Using the tensor virial method Chandrasekhar (1969) has given a uniform analysis of the classical result. The classical results have been extended by Hachisu and Eriguchi (1984a, b) who looked for the onset of instability in polytropes in binary orbits.

Of the metre-wavelength solar radio bursts which have been recognized, those of type II are characterized by the most complex set of spectral features. Apparently acceptable explanations have now been put forward for most of these features. However, not all these explanations can be considered to be established. In particular the phenomenon of band splitting has been explained in different ways by Sturrock, by Tidman et al., by Zheleznyakov and Zaitsev. However, the theories of Sturrock and Tidman apparently require magnetic fields so strong as to preclude the formation of a magnetohydrodynamic shock wave by a disturbance moving at the velocity (<~ 1000 km/s) attributed to type II bursts. The same problem is encountered in other earlier theories of band splitting involving magnetic effects. The other theory does not involve the magnetic field strength. However, the details of this theory do not appear to have been properly worked out as yet.

The authors analyse four high-dispersion IUE spectra of HD 184279 observed in 1979 and 1982.

Henry Abraham died on 9 December 1985. A few days earlier, he explained to me the work he had been doing in recent years, and gave me responsibility for his documents and notes. Amongst them were the manuscript for the above paper, prepared about 1979 but not submitted for publication then, and meticulous and extensive notes which examine further the questions raised by the paper. It has seemed to me to be appropriate to submit for publication the above paper as he wrote it, and to add a summary of his subsequent work as I interpret it.

The University of NSW’s Automated Patrol Telescope is a modified Baker-Nunn satellite tracking camera, now used for CCD imaging of astronomical objects. The f/1 Baker-Nunn optical design gives a 30° field of view with an approximately spherical focal surface of radius ≈500 mm. While the focal plane curvature is tolerable across the 1.4° × 1.0° field of the present CCD, it becomes unacceptable when a larger CCD is used. In addition, the use of glass filters in the highly convergent beam produces intolerable spherical aberration. We present a design modification to the original Baker-Nunn which enables a 5° diameter flat field to be produced when using B, V, R or I filters. By making this modification, we plan to perform multicolour imaging, using a new large-format CCD with a 2.9° × 1.9° field of view.

It is now firmly established that a small anisotropy of the galactic cosmic rays exists, observable from Earth as a variation of intensity in sidereal time. The problem now is to determine more clearly the characteristics of the anisotropy and, in particular, its detailed spatial structure and how it depends upon the energy and composition of the cosmic rays. This is a very difficult task and, in the final analysis, may not be fully achievable from Earth-based observations. The purpose of the present paper is to describe briefly an installation now operating in Tasmania to provide further information on the spatial structure of the anisotropy.