Misner Thorne and Wheeler (1973), (page 629) suggested that a freshly formed White Dwarf star of several solar masses would, if slowly — rotating, collapse to form a neutron star pancake which would become unstable and eventually produce several, possibly colliding, neutron stars.

In astrophysics the polytropic law with index n is commonly used as a means of imposing a simple and ordered physical structure on a gaseous (or smoothed discrete) system. In many instances it would be preferable to be able to introduce a polytropic density variation analytically into the basic theory rather than numerically at the computational phase. It is perhaps unfortunate that the three well known classical analytical E type solutions of the Lane-Emden equation for n = 0, 1 and 5 all have some constraining physical features; specifically, the polytrope n = 0 has uniform density and hence arbitrary radius, when n = 1 the mass and radius are independent of each other and the solution cannot be transformed homologically, and because the first zero ξ1 = ∞ for n = 5 the corresponding polytropic model has infinite extent and central condensation. In contrast, and unlike most stars, the two finite radius models have central condensations which ~ 1.

Evidence exists for mode energy changes in beat Cepheid variable stars over the 20-30 year interval during which photoelectric observations of the objects have been obtained. For TU Cas, Hodson, Stellingwerf and Cox (1979) have found that the first overtone amplitude has been decreasing with time from 0.4 to 0.25 mag over a 67 year timebase; these authors also included some early visual estimates in their analysis. For U TrA, Faulkner & Shobbrook (1979) have found that the first overtone pulsation has been increasing relative to the fundamental over a twenty year timebase.

Second harmonic plasma emission is attributed to the coalescence of two Langmuir waves into a transverse wave.

The eclipsing variable SV Cen was observed differentially in the UBV system with the 60cm reflector at Perth Observatory (1974-75) and with the 41cm reflector at Siding Spring (1975-79). Individual measurements have either been published in the IBVS or will be published there soon.

In the astrophysical context, where the effects of a magnetic field on stellar convective processes have to be taken into account, we have ϰ > > η > > ν (Weiss 1977) where ϰ, η and ν are respectively the thermal, magnetic and viscous diffusivities.

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.

DI Peg has been recognised as an eclipsing system since 1934 when Morgenroth (1934) discovered its variability. For over fifty years, many observers [Jensch (1934), Opalski (1936), Tsesevich (1954), Szafraniec (1956), Kruszewski (1956), Huth (1966), Rucinski (1967), Binnendijk (1973)], have studied this system. DI Peg was observed at Midway Observatory (M.O.) during 1976 and 1977 (Kennedy 1978). Considering the erratic period changes of the system, it appeared desirable to check the system again during 1980.

The proposal that the complex spectral line changes seen in the large amplitude β Cephei variable BW Vul resulted from a shock effect, driven by an underlying radial pulsation, was first made by Odgers (1955). Stamford and Watson (1978) examined some suitable atmospheric models for this star, which were driven by a hard subphotospheric piston under an isothermal assumption. These models displayed strong shock development and had some encouraging similarities with the BW Vul phenomenon. However, particularly because of the use of a hard piston, they were not very physically realistic. Here we discuss the results of a more sophisticated approach to this modelling problem. This modelling problem is of specific current importance because Odell’s (1981) recent observations of a variable polarization in BW Vul have renewed the debate over possible nonradial pulsations in this star. Since nonlinear effects are clearly substantial in BW Vul, it is evident that the implications of these on the observed spectral line changes should be carefully examined on a radial pulsation hypothesis, before turning to the complexities of nonlinear nonradial profile modelling.

Sources of the Type I storms are thought to lie on closed magnetic loop systems above bipolar sunspots. Usually one sunspot is stronger than the other in the bipolar magnetic structure, and accordingly only one radio source associated with the stronger sunspot is usually observed. Occasionally however a double radio source is observed in conjunction with the bipolar sunspots. In such a case the double radio source should be intrinsically bipolar, viz. the two components should emit opposite senses of circular polarization (in this paper we use the word polarity for simplicity).

The nearest star α Centauri is a triple system. The star α Cen, one of the pointers to the Southern Cross, is itself a −0.3 mag visual binary consisting of a α Cen A, a G2V star popularly considered to resemble the Sun, and α Cen B, a KOV star. The orbital period is 80.089 years, the semimajor axis is 23.5 AU, the distance 1.34 pc, the masses are 1.11 and 0.92 (±0.03) M⊙ (Kamper & Wesselink 1977). The third star, Proxima Cen (V645 Cen) is a faint common proper-motion companion separated from α Cen AB by about 2°. It is known to most people only by virtue of being slightly closer to the Sun than is α Cen A, and therefore actually the closest star.. This 11th mag flare star is undoubtedly coeval with a α Cen AB, but being the least massive by a considerable margin, may have been ejected from the system shortly after formation.

The discovery of the variability of the eclipsing system UX Eri can be attributed to Soloviev (1937). Photographic observations were made by Zessewitsch (1934, 1954), Bodokia (1938) and Gaposchkin (1953). Photoelectric observations were obtained by Kitamura and Nakamura (1957). The most recent photoelectric data were obtained by Binnendijk (1967) who determined new orbital elements. During the 10-year period from 1967-1977 the variable appears to have received little attention.

Guthnick and Prager (1929) were the discoverers of the variability of AH Virginis. Prager (1929) produced a photographic light curve the same year. Lause (1934, 1935, 1937) observed the system visually and improved the period as deduced by Prager. Further visual work on the system was done by Zessewitsch (1944). The first photoelectric observations came from Huruhata and Nakamura (1951), followed in 1952 by Kitamura, Tanabe and Nakamura (1957).

Lack of their data on ingress and egress at primary eclipse resulted in the mean curve showing a rounded bottom during minimum light. From this, an inclination of the system of 61° was derived by Kopal and Shapley (1956). Two years later, Kwee (1958) revealed primary minimum to be flat bottomed; the light remaining constant for some 40 minutes. This was confirmed by Binnendijk (1960), thus classifying AH Virginis as one of the few W UMa systems which display complete eclipses at an inclination likely to be closer to 90° then to 61°. Observations of the present study confirm constancy of light of 40 minutes duration during primary minimum. Assuming i = 90°, a new orbital solution was derived by Kitamura and Takahashi (1959) showing constant light for both minima. Binnendijk’s observation, however, showed a curved appearance at secondary minimum. The present observations indicate curved as well as flat secondary minima.

Distributions in longitude of solar radio bursts often are compiled by identifiying the position of the burst with the position of the associated H-Alpha flare. Early work on the longitudinal distribution of type II bursts compiled in this way (eg. Maxwell and Thompson 1962) indicated an approximately uniform distribution. Subsequently Svestka and Fritzova — Svestkova (1974) and Svestka (1976) published a distribution of 244 H-Alpha flares with which type II bursts were associated (hereafter called type II flares) that showed marked deficits near central meridian and the limb (Fig. 1). They suggested that the distribution was a product of propagational selection, being in some way dependant on the nature of the type II source mechanism as well as the manner by which the radiation reached the observer. On this basis they argued that the number of type II bursts that occurred near central meridian and near the limb was underestimated.

The cyclotron line in Her X-1 is a hard X-ray feature at ≈ 58 keV discovered by Trümper et al. (1977). A cyclotron emission line at about this energy had been predicted by Gnedin and Sunyaev (1974) and Basko and Sunyaev (1975). They developed a model for the infall of accreted matter onto a magnetized neutron star’s surface, and concluded that hot spots would form at the polar caps and radiate X-rays. They predicted that the optional depth for bremsstrahlung would be less than unity, that for Compton scattering greater than unity and that for cyclotron absorption much greater than unity. A cyclotron line is then implied due to the emission spectrum lying below the black-body spectrum except near the cyclotron energy where it rises up to the black-body limit. More recent developments of these background ideas have been reviewed by Börner (1980).

I shall outline the physical principles on which I believe pulsar magnetosphere models should be based. The principles follow from the equations of continuity and motion for each species and the two sourceless members of Maxwell’s set of equations, together with the steady-rotation constraint and boundary conditions at the stellar surface.

Since the discovery of the first asteroid by Piazzi in 1801, orbits have been determined for over 2500 with varying degrees of quality; 2357 have been assigned permanent numbers as of this writing (Marsden and Bardwell 1981).

Solar type III radio bursts often occur for prolonged periods (≳ 1 hour) with small time intervals (≲ 1 minute) between bursts. Such phenomena usually are confined to decametre wavelengths (frequency ≲ 100 MHz) and are called ‘type III storms’ (e.g. Stewart and Labrum 1972).

The properties of the M dwarfs have been investigated by spectroscopic and photometric observations of over 150 red, high proper motion stars. Most of these stars have red magnitudes fainter than 12 magnitude.

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.