The primary function of the 64-m telescope, situated at Tidbinbilla near Canberra, is to communicate with and to control NASA’s unmanned interplanetary space craft (Reid et al. 1973). Similar telescopes are situated at Goldstone in California and in Madrid and are part of the NASA-JPL Deep Space Network (DSN). Under the Host Country Radio Science Agreement between the U.S. and Australia the telescope is available to Australian astronomers at times outside those committed to normal tracking. A radiometer operating atλ = 13.5 mm has been built by CSIRO for use on the 64-m telescope. It was initially used for VLBI observations of water vapour masers on baselines between the U.S., Australia and USSR (Batchelor et al. 1976).

The object EX Hya is a dwarf nova with a binary period of 98.3 min (Mumford 1964, 1967). Warner (1972, 1973a) has observed two complete cycles of this star with a photoelectric time resolution of 5 sec. These observations suggested that EX Hya can be understood in terms of the model proposed by Warner and Nather (1971) in their discussion of U Gem. In this model, a white dwarf primary of a semi-detached binary system is surrounded by a disk of gas formed from matter transfered from the secondary, which is a cool dwarf star filling its Roche lobe.

That the parent masses of white dwarf (WD) stars can exceed the Chandrasekhar limit of approximately 1.2 can be seen from star clusters that have turn-off points in excess of this mass and still contain WD. Auer and Woolf argued that WD in the Hyades and Pleiades is evidence that stars with masses larger than 2.5 can become WD. Sandage and Jones have used the luminosity function to compute the number of WD expected in several clusters. Jones estimated that the brighter of the two WD sequences arises from stars of mass greater than 1-9 Schwarzschild, for example, has stressed the importance of a knowledge of the resulting mass-loss. Deutsch has discussed mass-loss from red giants and Faulkner has summarized the relationship between the planetary nebulae and the WD. Nevertheless, the role of WD formation in the enrichment of the interstellar medium and the relationship between WD and their parent stars is unclear.

The causes of various traits of the polar motion are still unknown or uncertain. For exploring these the Chandler nutation has the advantage of being readily observable and it should be independent of external torques. This nutation shows a prograde motion of the earth’s axes of rotation and of excitation about each other. For simplicity the positions of the poles of rotation P and excitation ψ (Munk & MacDonald, 1960) are given in terms of dimensionless excitation functions which apply in principle whether they come from distributions of mass, relative motions or torques. Let O be the pole of zero excitation and R be the angular distance between P and ψ.

A simple model for solar flares is described which invokes many ion-acoustic double layers in the source region. The ability of the model to explain some of the observed characteristics of solar flares is discussed, particular attention being paid to the well-observed high-energy flare examined by de Jager et al. (1987).

Primary cosmic rays passing through the solar system carry with them valuable information about solar and astrophysical phenomena in the form of intensity and spectral variations. In order that this information be efficiently extracted from observations of the directional cosmic-ray flux at the surface of the Earth, it is essential to have accurate information available to enable the relating of the observed secondary cosmic-ray directions of motion and intensity to those outside the range of the disturbing terrestrial influences.

Angular diameters of Magellanic Cloud planetary nebulae obtained using speckle interferometry on the AAT are presented. The mass of ionized gas in each nebula is derived from the angular diameter and published Hβ line fluxes; the derived masses range from 0.005M⊙ to 0.19M⊙, with a mean value of 0.08M⊙. All the planetary nebulae observed are relatively small (diameter ≲0.13pc), young (age ≲ 2500 years), bright and dense. They are therefore almost certainly only partially ionized, so that the masses derived for the ionized parts of the nebula are lower limits to the total nebula mass.

Perhaps the most direct evidence to date for shock wave acceleration of electrons in the solar corona is provided by radio observations of Type II bursts containing herringbone structure (Roberts 1959). On spectral records the herringbones appear to resemble miniature forward and reverse drift Type III bursts extending above and below the Type II backbone.

A Photometrics CCD system containing a TH7882 chip has been in use at Mt John since 1989 October for imaging photometry. Extra control software has increased observing ease and image-header information. Photometrically the system appears to be performing satisfactorily. The blue helium star LSS 99 showed no variation exceeding ~ 1% over 40 min of observation. The blue eclipsing binary HV 1761 in the Small Magellanic Cloud is found to have approximately equal components.

The MC2 and MC3 catalogues cover two strips approximately 2° wide centred on declinations +11° and +16.5°. MC2 runs from 11h 28m to 01h 23m and MC3 from 13h 31m to 04h 11m (Sutton et al. 1974). Optical identifications up to 17h 00m have been’published (Hazard and Murdoch 1977) and identifications for the remainder exist in preliminary form (Hazard, Zotov and Murdoch, in preparation). Optical spectra are being obtained chiefly at Lick Observatory (Smith et al. 1977) and this programme is now approaching completion.

Observations of the distribution of millimetre-wavelength brightness over the quiet Sun provide an important test of models of the solar chromosphere. The author and colleagues have recently carried out two investigations of the quiet-Sun brightness at 3 mm wavelength — one by means of a total eclipse observation (Labrum et al. 1978) and the other by aperture synthesis with a two-element interferometer (Archer et al. 1978). I present here a preliminary discussion of these and other measurements of millimetre-wavelength brightness distributions and of their interpretation in terms of chromospheric structure.

Many cold molecular clouds have been detected as a result of their association with dense optical obscuration. The HII region RCW 36 is contained within a prominent dust lane extending several degrees along a line of almost constant right ascension (see e.g. Rodgers et al. 1960). By means of H2CO and OH observations we have found that this lane is associated with a dense elongated molecular cloud.

The pulsar 0833-45 associated with the Vela supernova remnant has been known as a strong source with fairly constant pulse amplitude since its discovery (Large, Vaughan & Mills 1968) using the east-west arm of the Molonglo telescope. The pulse stability together with the short period of 89 ms allowed its integrated flux to be seen also as a 1.7 Jy point source with the pencil beam of the full Cross, and a more precise declination was obtained. Further observations in 1971/72 with a beat period integrator used on the fan beams of the north-south arm showed that the pulsed radiation had the same declination as the point source within 2 arcsec (Vaughan & McAdam 1973). Monitoring observations in 1975/76 gave an independent position, and the mean of all Molonglo (408 MHz), Fleurs (1415 MHz) and NRAO interferometer (2700 MHz) positions led to the optical detection of the pulsar (Goss et al. 1977). The point source, therefore, is reliably identified with the pulsar.

Although the radio continuum distribution of the HII-region/molecular-cloud complex W33 (peak l = 12°.8, b = -0°.2) resembles a discrete region about 15′ arc in size, the behaviour of the recombination-line velocities (Gardner et al. 1975; Bieging et al. 1978) and molecular-line velocities (OH: Robinson et al. 1970; H2CO: Gardner and Whiteoak 1972) has been difficult to interpret in terms of a simple model. There is a difference of opinion as to whether W33 consists of two independent complexes at different distances along the line of sight or a single expanding complex (e.g. Goss et al. 1978).

The existence of a group of magnetic white dwarfs with mean surface fields of between ~5 × 106 G and ~2 × 1O7 G is now firmly established through the discovery of Zeeman structure in hydrogen and helium lines (Angel et al. 1974, Liebert et al. 1975, Wickramasinghe et al. 1977, Martin & Wickramasinghe 1978, Liebert et al. 1977). There is considerable evidence from polarimetric studies for even higher fields in some white dwarfs (Angel 1977). Most of these stars are cool and show nearly continuous spectra or weak unidentified absorption features. The possibility of cyclotron absorption in white dwarfs was first discussed in connection with the infrared polarisation spectrum of one of these stars, Grw + 70°8247 (Kemp 1970). More recently the polarised white dwarf GD229 was found to have a rich optical spectrum with a strong feature at λ4185, for which cyclotron absorption has been mentioned as a possible origin (Angel 1977, Greenstein & Boksenberg 1977), though without supporting computations. In this letter we use models to investigate this possibility further.

The radio emission associated with SN 1987A appears to be synchrotron emission resulting from the acceleration of electrons at the interface between the outward moving shock wave and clumps of circumstellar material. The Australia Telescope Compact Array is now able to resolve this region, which has dimensions of ~ arcsec, revealing a slight (10%) asphericity in the distribution of the low density gas within the [OIII] circumstellar ring. Assuming that the radio emission arises from a region just behind the shock front, we deduce a mean radial expansion velocity, from 1987 to 1992, of 29 200 kms. First observed contact of the shock with the [OIII] circumstellar ring could occur as early as mid-1993, depending on the deceleration in the intervening gas. This will probably be closely followed by shock-excited optical lines, a strong X-ray outburst and a further increase in the radio emission.

There are three non-thermal sources in the Large Magellanic Cloud which are recognized as supernova remnants. They are N49, N63A and N132D in Henize’s catalogue; a summary of their observing history is given by Westerlund and Mathewson (hereinafter referred to as ‘WM’). They are rather important to our knowledge of supernovae, as there are only four galactic supernova remnants (Cas A, the Crab, the Cygnus Loop and Vela) whose distances are known approximately from independent evidence. Since the distance to the LMC is well-known, the distance to sources in it is also known quite accurately.