We summarise the results, to date, of a long-term program of searching for flare stars in the region of open clusters selected on the basis of distance and age.

Correlation radiotelescopes have become increasingly important in the last few years in all types of astronomical observations. These instruments operate by multiplying (correlating) the outputs of two separate aerials in order to provide a composite antenna with a range of aerial spacings and orientations. As a general rule this range of spacings is truncated at both the largest and smallest spacings, the largest spacing being determined by the area available or by the cost of the system, and the lowest spacing by either cross coupling between the multiplying elements (as in the Mills Cross type) or by the geometrical size of the elements (as in the compound interferometer type).

strong non-thermal radio sources at low galactic latitude may be young galactic supernova remnants or else distant extragalactic objects located in the direction of the galactic plane merely by chance. Here, we have imaged G321.48 + 1.02 with the Australia Telescope in order to distinguish between these alternatives for this source.

SN 1987A has been observed with a combined high energy γ-ray (50-500 MeV) and hard X-ray (15-150 keV) payload during a balloon flight on 5 April 1988 from Alice Springs, Australia. The γ-ray observations, along with our earlier ones on 19 April 1987 are the only such observations of the supernova to date. The γ-ray detector characteristics are described. The preliminary results of the recent flight and their implications in terms of the known supernova parameters are discussed.

The reason why some early-type galaxies contain powerful radio sources is not yet well understood, but it is often suggested that an external factor such as interaction with a neighbouring galaxy may be involved in triggering a radio source (Gisler 1976, Dressel 1981, Hummel 1981b). Radio emission may be enhanced in galaxies which have a close companion for several reasons, such as a gravitational perturbation or the possibility of gas accreted from the companion fuelling a central source. The latter effect might be expected to be more pronounced in elliptical galaxies, which are generally gas-poor (Faber and Gallagher 1976).

During the second half of 1986 tests were made of a new Q-band (43 GHz) receiver designed for the Parkes radio telescope. As part of the trial observation program 12 symbiotic stars were examined for SiO maser emission. No significant new emission was detected from any of the candidates, although several previously known SiO sources (including one symbiotic star) were confirmed. We conclude that potential SiO maser action near the Mira star in most symbiotic systems is prevented by the presence of the hot companion star.

In the five years since the last invited paper on model stellar atmosphere applications there have been many significant advances made on all fronts. The five aspects which I will cover in this paper are:

• (1) the results of white dwarf model atmosphere investigations;

• (2) the results of the inclusion of non LTE phenomena in the atmosphere computations of hot (T > 15,000 K) stars;

• (3) the probable understanding of the cause of peculiar abundance patterns in the Ap and Bp and Am stars;

• (4) the advances in theory and observations of cool star atmospheres; and

• (5) the use of synthetic spectra and colours.

One of the important discoveries of the present century is that the Universe expands. Two important parameters which define the dynamics of the Universe and can be obtained at the telescope are the rate of expansion zhqо , and change of this rate with time qо , It is difficult to derive a value for Hо because accurate distances of farther galaxies are needed. This involves identifying the luminous objects, such as brightest stars, HII regions, globular cluster, supernova etc., in the Local Group galaxies as well as in the external galaxies. Once the absolute magnitudes of these objects are calibrated with the known distances of the Local Group galaxies, distances to the external galaxies can be derived.

The main features of visual searching for supernovae in other galaxies by amateur astronomers are described, and an outline is given of the results which have been achieved so far by this method. A short comparison is made between visual searching and photographic searching. A more extensive comparison is then made between visual searching for supernovae in Australia, and the work of the Berkeley Automatic Supernova Search at Leuschner Observatory, since 1986. Among the conclusions is the claim that a competent visual observer could produce similar results to those produced by the Berkeley group if a telescope of similar aperture was used for a similar amount of observing time, and from a good observing site. Indeed, visual searching might possibly produce more results, and such a search would only cost a small fraction of what was spent on this automatic search. It would be a worthwhile project to conduct a visual search with a suitably designed 76-cm telescope, or a one metre telescope, over a period of a few years, to see if this conclusion could be supported in practice.

For many pulsars the integrated or mean pulse profile is highly polarized. Generally linear polarization dominates over circular and there is a continuous variation of position angle through the profile (e.g. Manchester 1971). In most models for the emission process the angle of polarization is related to the (projected) direction of magnetic fields in the source region. Several of the observed properties of pulsars, for example, the mode-changing phenomenon (Backer 1970) and the different spectral index of different components of the intergrated profile (Manchester 1971), suggest that different parts of the integrated profile are emitted in different (though closely related) parts of the source. The different observed position angles across the integrated profile would then result from different projected magnetic field directions in these different parts of the source. For many pulsars the observed position angle variations are closely represented by a path through a radial set of projected field directions such as would be obtained in the vicinity of a magnetic pole (cf. Radhakrishnan and Cooke 1969).

Over past decades many attempts have been undertaken to detect a statistically significant 11-year variation in tree-ring widths and thereby provide direct evidence for the influence of solar cycle activity on growth. The data were generally associated with arid sites and were found to contain no signal of any consequence at the equivalent frequency. However, our recent analysis of a tree-ring chronology established from spruce trees growing at a very high sub-alpine site in Colorado, has revealed the presence of a dominant 11-year spectral periodicity over the last 200 years. These growth cycles could arise from temperature changes due to variations in insolation and climate or from variations in direct radiation within a specific band.

We report continuum observations of the NGC 7538–IRS 1, 2 and 3 regions made with the NRO 45-metre dish between 43 and 90 GHz, and present a brief interpretation.

Type II solar bursts characteristically drift slowly from high to low frequencies at a rate of about 0.1 MHz/s, appear only at frequencies lower than 250 MHz, and frequently have harmonic structure, i.e. there are identifiable spectral features within the fundamental which are duplicated at twice the frequency. Thus it is clear that at least in some cases, true harmonic radiation is involved; the source region emits frequencies f and 2f simultaneously.

Survey type observations have been made with the Parkes radio-telescope of 4 galactic radio sources having either a non-thermal radio spectrum, or exhibiting shell structure in their emitting regions. Observations were made at a wavelength of 11 cm using the Parkes radiotelescope where the beamwidth is about 7.5 min.arc.

We describe a survey of metal rich K-giants at the SGP, and show how they can be used as a simple isothermal tracing population to derive the local density of matter and the component of acceleration K z perpendicular to the galactic plane.

The galactic nuclear bulge is a well defined population, but it is one that is relatively difficult to study in detail because its members never stray into the solar vicinity and they are both distant and obscured. Mould (1982) has summarized much of our knowledge of the masses and composition of stars in the bulge. The red giants resemble those in metal-rich old open clusters and the late M giants are either younger than galactic globular clusters or super-metal-rich or both. Whitford and Rich (1983) have demonstrated the existence of K-giants that are super-metal-rich in iron and Wood and Bessell (1983) have interpreted the properties of a sample of long period variables in the bulge as those of a young, super-metal-rich population.

The ‘holographic’ technique for accurately measuring the surface figure of large reflector antennas, described by Bennet et al, (1976) and Scott and Ryle (1977), has many advantages over older conventional survey methods. These include high speed, low cost, and the absence of any need for additional complex mechanical or optical survey devices. In essence, the technique consists of measuring the complex far-field response of the antenna at a single frequency using a terrestrial, satellite-borne or celestial radiation source of small angular diameter. This two-dimensional pattern is then Fourier-transformed to yield the complex illumination function across the antenna aperture. Antenna surface deviations are manifested as phase fluctuations in this function. In practice, a second antenna is needed to provide a phase reference.