The Chatterton Astronomy Department has constructed an 11.4 m baseline prototype stellar interferometer as part of its long term programme of high angular resolution astronomy. The background and present status of the instrument is described.

We describe the application of Peltier effect cooling to charge coupled device (CCD) detectors. We are developing this technique to produce a CCD camera which requires low maintenance, yet has sufficiently small dark-current for long exposure imaging. This camera will be used in an automated imaging telescope at Siding Spring Observatory. The design principles used to maximise cooling of the detector, and hence minimise dark-current, are discussed. A small dark-current can be obtained only if great care is taken to reduce or eliminate convective, conductive and radiative heating of the chip. In addition, a path of high thermal conductivity must be provided for the heat removed from the CCD. A recent laboratory test of our cooling system demonstrates that careful design can lead to sufficiently low CCD dark-current for many astronomical applications.

Magnetic fields of about 1012 G have now been measured in several astrophysical objects (Trümper etal. 1978, Wheaton et al. 1979, Mazets et al. 1981). In the case of pulsating X-ray sources, the presence of a companion star indicates that accretion is probably the energy source for the X-rays.

From the Lyon-Meudon Extragalactic Database (LEDA) we constructed a sample of 27000 galaxies with radial velocities smaller than 15 000 kms−1. From this first sample we selected the 5683 largest galaxies, which constitute a sample complete up to the diameter limit D 25 = 1·6′. This sub-sample has been used to search for the most populated plane. The result is that the plane defined by the pole (l = 52°; b= 16°) contains twice as many galaxies as would be found for randomly distributed galaxies. This plane is not far from the supergalactic plane. The distribution of galaxies in this plane has been studied by using the radial velocity as an estimate of the distance. An excess of galaxies appears at a distance of about 70 Mpc. We discuss the reality of this density enhancement which could result from selection effects.

Three-wave interactions involving two high-frequency waves (in the same mode) and a low-frequency wave are discussed and applied to pulsar eclipses. When the magnetic field is taken into account, the low-frequency waves can be the ω-mode (the low-frequency branch of the ordinary mode) or the z-mode (the low-frequency branch of the extraordinary mode). It is shown that in the cold plasma approximation, effective growth of the low-frequency waves due to an anisotropic photon beam can occur only for z-mode waves near the resonance frequency. In the application to pulsar eclipses, the cold plasma approximation may not be adequate and we suggest that when thermal effects are included, three-wave interaction involving low-frequency cyclotron waves (e.g. Bernstein modes) is a plausible candidate for pulsar eclipses

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.

Thorough investigation of clusters of galaxies involves the complete modelling of their dynamics and structure. Presented here is a description of such a substantial project utilizing a sample of several rich southern clusters of galaxies. Incorporating results from radial velocity analyses of cluster galaxies and X-ray images of the clusters into rigorously constructed models of the cluster potential well and atmosphere will enable the dynamics, structure and evolution of clusters to be tied down.

This paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

The HR 1614 moving group of stars (Eggen 1978a) is one of a number of such groups identified by Eggen from amongst the disk population of the Galaxy (see e.g. Eggen 1969). The group was selected from a sample of 44 field stars south of + 30° declination, with right ascensions mainly > 12h and <2h , and with motions similar to that of the star HR 1614, which has a velocity of (U, V) = (−1, −58) km s−1, where U and V are the components of space motion in the direction of the galactic anticentre and galactic rotation respectively, measured relative to the Sun. The colours of these 44 stars, when plotted in a (b-y, R-I) diagram, were such that 26 of them had an excess blanketing of ~ 0.03 in b-y, measured with respect to the Hyades group. This excess blanketing was consequently chosen to be a criterion for group membership.

Studies have been made of the extent to which extragalactic cosmic rays observed at the earth would be deviated by the galactic magnetic field. The distribution of these deviations is presented as a function of observed direction for two field models. Also using these two models, possible extragalactic directions are derived for the cosmic rays detected by the SUGAR giant air shower array as a basis of a possible technique for searching for extragalactic cosmic ray sources.

We present a progress report on the dynamical analysis of the IRAS sample of OH/IR stars. This sample is complete within a distance of 8 kpc. We distinguish two groups of OH/IR stars, one with high and the other with low expansion velocity of the circumstellar shell.

Using a quadratic programming method we fit a database of Galactic orbits to the observed distribution of radial velocities, longitudes and latitudes. The dynamical model yields a distribution function, based on two integrals of motion, for each group. Integration gives the density, the mean velocity and the velocity dispersions as function of R and z. The distribution functions for the two groups differ enough to suggest that they represent two different stellar populations.

We estimate the stellar lifetime for each group by comparing the velocity dispersions and z scale-heights at the solar radius with those found for local stellar populations. We conclude that the group with the low expansion velocity is likely to be part of the thick disc, while the high expansion velocity group has dynamical characteristics resembling an old disc population; this in contrast with the findings for differently selected samples of OH/IR stars (e.g., Baud et al. 1981a; 1981b), which were found to be less than 1 Gyr old.

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.

We are studying the distribution and morphology of magnetic fields in southern face-on and edge-on galaxies with the intention of clarifying the distribution, lifetimes and transport mechanisms of cosmic rays, and investigating the intensity and orientation of the disc, halo and poloidal magnetic fields. As a preliminary study, before the Australia Telescope was available, we observed a sample of well-known southern spiral galaxies with the Parkes radio telescope.

Here, we present the resulting polarisation images for three galaxies, NGC 253, M 83 and NGC 4945, which were observed at 4.75 GHz and 8.55 GHz. The corresponding total power contour plots have been already published by Harnett et al. (1989a, 1990).

During the period 1966 July 12 to August 5 observations were made of the Sun at three radio observatories. The instruments used were the east-west arm of the Mills cross at Molonglo (408 MHz) and the Christiansen cross at Fleurs (696 MHz and 1424 MHz). The aim of these observations was to study the discrete sources of the slowly varying component of solar radio emission, while activity was comparatively quiet. The three frequencies enabled the variation of source structure with height of solar atmosphere to be studied. It has been pointed out by Swarup et al., and Christiansen et al. that the determination of the frequency dependence of these discrete sources is important for defining the physical mechanisms causing the radio emission.

The Australia Telescope Compact Array has been used for observations, with arcsecond resolution, of the HII region N159 in the Large Magellanic Cloud. Images at 5 GHz reveal a second compact continuum component which has no obvious counterpart at optical and infrared wavelengths. Observations of HI 10α recombination-line emission, and HI and H2CO absorption, suggest that the object is a compact HII region embedded in a dense obscuring cloud on the edge of N159.

Worm-gear drives for astronomical telescopes have associated with them certain requirements which cannot be effectively dealt with by applying standard design methods and parameters, since these drives differ in many ways from conventional power transmission gearing.