We have compared the spectra of six Type Ia supernovae, at ages between 4 and 404 days after maximum light, to see whether all show similar evolutionary behaviour. We find that the spectral lines between 6800 Å and 8000 Å follow a smooth evolutionary trend, but that lines redward of 8000 Å show significant differences. SN 1987I and SN 19880 show extra emission over a broader wavelength region, possibly due to OI 8446 Å emission which would indicate higher envelope densities for these objects. Our results are consistent with the trend of expansion velocity with parent galaxy type reported by Branch and van den Bergh (1993). Variations within the class of Ia SNe may affect their use as standard candles.

Theoretical investigations of non-linear convective motions quite often assume that either the Boussinesq or the anelastic approximations can be used.

The aggregation of a large number of planetesimals into a single body is a problem that has proved to be a stumbling block for many theories of planetary formation. This difficulty has mainly arisen because of the tendency of an orbiting stream of bodies to disperse over the equatorial plane as a result of the combined effects of collisions and gravitational interactions (Trulsen 1972; Brahic 1975). Once such a chaotic distribution of orbiting bodies has developed, it is extremely difficult for these bodies to subsequently accumulate into a single entity. This problem does not arise, however, when aggregation takes place within a differentially rotating gaseous ring as proposed by Prentice (1978). It has been shown previously (Hourigan 1977) that the gas drag overcomes the disruptive nature of collisional interactions, resulting in the formation of a thin concentrated torus of orbiting bodies.

An instrument is described that can detect clouds at night-time by sensing their infrared emission. The device can readily detect clouds that are difficult to see with the unaided eye on a moon-lit night. It can be used to provide an indication of how photometric the conditions are, to terminate exposures when cloud forms, and to close the dome when conditions become unsuitable for observing. The detector also has applications as an astronomical site-surveying instrument.

Mestel, Wang and Westfold (1984; ‘MWW’) have recently introduced a pulsar magnetosphere model in which electrons leave the star with non-negligible, but not highly-relativistic, speeds, and flow with moderate acceleration along magnetic field lines before reaching a limiting surface, near which rapid acceleration occurs. Such moderately accelerated flows are analysed here. A second class of flows, which do not encounter a region of rapid acceleration, is found.

This note describes a method of image formation which i applicable to radio astronomy. AH the information simultaneously reaching an aerial array from an extended region is utilized to produce the image so that the maximum sensitivity is realized. The method is simple in principle and involves relatively few components. One stage of the data processing presents some technical difficulty, but it is believed that particularly for observations below about.

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 Extreme Ultraviolet Explorer (EUVE) is a NASA funded astronomy mission which will operate in the 70–760Å spectral hand. The science payload has been designed and built by the Space Sciences Laboratory at the University of California, Berkeley and consists of three grazing incidence scanning telescopes and an EUV spectrometer/deep survey instrument.

We give an overview of the planned mission profile and briefly discuss the instrumentation which comprises the science payload. The EUVE is scheduled for launch in late August 1991.

Among the astrophysical researches which will largely benefit from observation from the Antarctic Plateau, we consider those which require high-quality, continuous, daylight, uninterrupted observation in the optical–near-IR region. The systematic study of the stellar micro-oscillations and surface activity of individual objects, as well as of stellar associations extended for periods of weeks, will make a fundamental contribution to our knowledge of stellar structure and will ultimately provide the physical parameters of the stars. A similar consideration applies for the short-period (a few hours to a few days) binaries, which include the W UMa contact binaries. These objects are subject to continuously varying light curves associated with surface activity and secular effects, which cannot be adequately studied from the currently available ground telescopes. Finally, the exceptional seeing and low background will allow the systematic search for and study of supernovae in clusters of galaxies at cosmological distances, which will improve our knowledge of the geometry of the Universe at z ~ 0·7–1.

The supernova rate in spirals of types Sc and Sd shows a sharp peak in face-on galaxies with inclination i ≤ 25°. This suggests that most supernovae in late-type galaxies occur in rich clusters or associations that are located at the base of chimney-like structures formed by a previous generation of supernovae. These chimneys are transparent because most of the dust contained in the rising column of gas within them had previously been destroyed in the hot bubble surrounding supernovae.

Since its discovery in 1964, interplanetary scintillation has become recognized as a valuable method for investigating the solar wind and the small-scale structure of the interplanetary medium. A particular advantage of the method lies in the ability to study those regions of the medium outside the plane of the ecliptic. To date little has been written about the relation between interplanetary scintillation and solar activity, although regular observations of the source 3C48 during 1965-6 have indicated that a small correlation may exist between the scintillation index and sunspot number. It also appears that anomalous increases in the scintillation index are, on occasion, related to strong flare activity on the Sun.

The basic model for the precipitation of trapped energetic particles from a magnetic flux tube is Kennel and Petschek’s (1966) model. Their model is symmetric, implying equal precipitation rates at the two feet of the flux tube. We have developed a model for precipitation in an asymmetric flux tube (Melrose and White 1979). Here we explore some of the consequences for the precipitation model of Melrose and Brown (1976) for solar hard X-ray bursts. In Melrose and Brown’s model roughly half the X-rays arise from precipitating electrons. With present instruments it is not possible to resolve the two feet of the flux tube. However, if the feet can be resolved, either directly by future X-ray telescopes, or indirectly through secondary optical, UV or radio observations, then, as we shall show, the additional information obtained could be used to derive information on processes in the magnetic trap.

The major programs at the Molonglo Radio Observatory are nearing completion. Much can still be done using the existing 1 mile Cross-type radio-telescope (Mills et al. 1963) but, to tackle properly many of the current problems in radio astronomy, a fundamental change is required from a transit to a trackable radio-telescope, combined with an increase in the operating frequency and the resolution.

The Fokker-Planck equation has been used by a number of authors (Jokipii 1966, 1971; Hall and Sturrock 1967; Hasselmann and Wibberentz 1968; Roelof 1968) to deduce the diffusion coefficients of cosmic-ray particles in the interplanetary magnetic field. However, these calculations suggest that the diffusion of particles perpendicular to the mean magnetic field is implausibly large; so large that the validity of a Fokker-Planck approach as applied to the interplanetary medium must be doubted.

We present preliminary results from a number of deep radio polarization surveys being made of the Magellanic Clouds at 2.3 GHz, 4.75 GHz and 8.55 GHz. Extended and linearly polarized radio emission has been found at 2.3 and 4.75 GHz from both the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). However, as the analysis of these data is not yet complete we present only some of the 4.75 GHz results at this time.

In the past decade, planetary nebulae have assumed considerable importance in elucidating our understanding of the final stages of stellar evolution at low mass. This began with the work of Shklovsky, O’Dell and Seaton, who showed not only that the nuclei of these nebulae were among the hottest stellar objects, but also that they evolved on a track in the Hertzsprung-Russell diagram (the Harman-Seaton sequence) on a time scale very rapid by stellar evolutionary standards (~ 20,000 years).

In science we have good, successful laboratories and scientists and we also have wasteful, inefficient and unproductive ones. The differences are not matters of chance.

It is not an accident that just one Cambridge College, Trinity, has achieved more Nobel Prizes than all of Japan. There was something in common amongst the Nobel prize winners Todd, Adrian, Perutz, Bragg, Crick, Ryle, Hewish and Mott that I was fortunate enough to meet and, in some cases, get to know well. Of course there was the personal and intellectual calibre of these people, their drive and determination. But also, there was the laboratory culture within which they worked, a culture still benefiting from the influence of Maxwell, Thomson and Rutherford.