Balloon borne alt-azimuth mounted X-ray telescopes flown from Hyderabad, India (17°N), Palestine, Texas (32°N), and Mildura, Australia (34°S), have detected hard X-rays (hv>20KeV) from discrete sources in the Cygnus region.

In the past a number of analytical solutions have been found to the differential equation for small radial adiabatic oscillations of stars, with the aid of a series expansion of the form leading to a two-term recurrence relation.

The advent of new techniques to measure the global oscillation spectrum of the Sun has provided a new and powerful tool to investigate solar structure. One of the most challenging and potentially rewarding problems in contemporary astronomy is to devise techniques which will allow similar studies of other stars. This paper outlines the theory of global oscillations of late-type main-sequence stars, and summarises some of the achievements of global oscillation studies of the Sun. It then reviews the very few successful attempts that have been made to study stellar oscillations, and briefly discusses several apparently promising lines for further instrumental development.

It is well known that the wings of the solar sodium D-lines cannot be predicted successfully using present line-broadening theories and elemental abundances derived from an equivalent-width analysis of the weak lines. By far the most important cause of broadening of the D-lines is collision broadening by neutral hydrogen.

In this paper we summarize the results of radio studies of the distribution functions (number, energy distribution and pitch angle distribution) of the energetic particles that are produced at the time of solar flares. We consider the clues and constraints they impose on the mechanisms of acceleration, bearing in mind that radio evidence implies that there are at least two stages of acceleration in many flares.

In the following sections we discuss the distribution functions of the particles resulting from (a) first phase acceleration, (b) first and/or second phase and (c) second phase acceleration. Table I summarizes the results.

Radio position measurements with an error of <2” arc rms allow reliable optical identifications of compact radio sources to be made solely on the basis of radio-optical position coincidence. In this way neutral or red stellar objects, faint compact galaxies and faint QSOs can be reliably identified. Such identifications are of particular interest because they are rich in BL Lac objects, high-redshift QSOs, QSOs with unusual optical emission or absorption spectra and galaxies with active nuclei (see Jauncey et al. 1978).

Most of the recent advances in X-ray astronomy have resulted from satellite observations in the low energy (< 20 keV) range. The Einstein X-ray Observatory in particular has been responsible for a dramatic increase in our knowledge of the X-ray sky, in that all major classes of astronomical objects have been detected.

The conventional method of measuring the radiation diagram of an antenna is to rotate it in the field produced by a fixed point source located in its Fraunhofer zone (Hollis et al. (1970)). With the very large antennas typically used in radio astronomy this presents difficulties. For example, to measure the 64 m telescope at ANRAO, Parkes at frequencies in the OH transition lines band (1.6-1.7 GHz), the source, to be located in the Fraunhofer zone, must be located at least 50 km away and then at a sufficiently high angle to allow measurements free from ground effects to be made. Clearly there are no terrestrial means to accomplish this.

The cosmic ray ground-level enhancement (GLE) of 24 October 1989 was the last of a series of GLEs associated with the same solar active region. Intensity enhancements were observed by at least 31 neutron monitors in the worldwide network, with the largest increase (~200%) observed at South Pole, Antarctica around 20:30 UT. Using a least-squares model fit to all available neutron monitor data, spectra, apparent source directions and particle pitch angle distributions have been derived. The effect of disturbed geomagnetic conditions has also been taken into account.

A new method for solving heat diffusion in three dimensional particle simulations is described. The difficulties encounted by other authors is discussed, in particular the difficulty of including boundary conditions in particle simulations. One and three dimensional tests of the method are described.

This paper discusses the observation of molecular hydrogen line emission outside near-infrared wavelengths, and in particular the opportunities afforded to molecular astrophysics by studies in the mid- and far-infrared.

Absorption limits the distances at which X-ray sources may be observed at low photon energies (≲3 keV). Several authors have estimated the X-ray absorption coefficients of the interstellar medium by assuming a chemical composition such as that given by Aller for the general abundances of the elements.

In calculating models of stellar interiors convection is almost always treated by assuming that it is present if and only if the Schwarzschild criterion is satisfied. It seems possible that this oversimplifies the actual situation. In particular convective motions may overshoot beyond the formal boundary of the convective core, as given by the Schwarzschild criterion. The principal result of such overshooting would be the mixing of additional material into the core. This sort of additional mixing has been considered by Maeder (1974) and by Prather and Demarque (1974) in relation to the evolution of stars away from the main sequence in old open clusters.

Prior to the advent of the Culgoora 80 MHz radioheliograph position measurements on type II solar bursts were restricted to those made with one-dimensional interferometers. These measurements yielded conflicting evidence on the apparent positions of fundamental and harmonic emission observed at a given frequency; different observers reported the fundamental to be closer to and further from the centre of the Sun than the harmonic. Here we report on two-dimensional observations at 80 MHz made on both fundamental and harmonic emission of a type II event that occurred on 1969 March 2. The observations are shown to be consistent with the hypothesis that the emission is produced as the result of a disturbance moving out from the site of a flare and forming a shock front within an overlying coronal streamer. Both fundamental and harmonic are explained by ‘forward’ emission from the shock front. Observations of the harmonic emission at 158 MHz are also consistent with this model.

We have designed a novel all-reflective optical system for an infrared camera. The camera gives a flat 5 arcminute field with a final focal ratio of f/2.5 when used at the f/15 focus of the Anglo-Australian Telescope (AAT). A 70mm diameter Fabry-Perot filter can be accommodated in a collimated beam, thereby giving narrow-band imaging capability. The design could readily be adapted to other telescopes and focal ratios. Its advantages are no chromatic aberration, no vignetting, no ghost images, low light-loss and excellent image quality.

The barometric coefficient of a cosmic-ray neutron monitor is found to increase with atmospheric depth from ~ 150 mm Hg to 600 mm Hg and then to decrease slowly with depth down to 760 mm Hg (Bachelet et al. 1965; Carmichael and Bercovitch 1969). Bachelet et al. 1965) tentatively attributed this change in the slope of the barometric coefficient versus atmospheric depth curve at 600 mm Hg to the contribution made by muons to the neutron monitor counting rate. Carmichael and Bercovitch (1969) have shown that the contribution to the monitor counting rate made by obliquely incident nucleons may be the real cause. Singh et al. (1970) have derived an expression for the barometric coefficient for vertically incident particles in a neutron monitor which increases continuously with increasing atmospheric depth down to 760 mm Hg, demonstrating more definitely that the above explanation of Carmichael and Bercovitch is correct.

We present UBVRI photometry of the faint and highly erratic cataclysmic variable discovered by Hawkins (1983) from a sequence of U.K. Schmidt plates. Observations using the ANU 2.3 m telescope over two nights in September 1986 show pronounced and repeatable modulation at a binary period of 108.6 min. Dramatic colour differences are evident in the folded UBVRI light curves: in the U band, a single sinusoidal peak is present, while at longer wavelengths, a second red peak dominates at a phase separation of Δϕ = 0.5. This behaviour is strongly suggestive of cyclotron emission from two magnetic accretion funnels in an AM Herculis binary system. Furthermore, the binary period lies in the narrow range of 100-115 minutes that characterizes most of the AM Herculis variables lying on the short side of the 2-3 hour period gap. We conclude therefore that the object is almost certainly a new AM Herculis system, and develop a model in which the blue and red components originate from two non-diametrically opposed cyclotron regions that are characterized by differing electron temperatures and opacities. Predictions are made regarding the linear and circular polarization properties of this important new magnetic variable.