During the last few years, a new type of radio object has appeared in the literature: this is the Early Type Emission Line Star, or ETELS for short. These objects are possibly the most interesting radio object discovered since the pulsars. They are certainly more easily understood, since an explanation of their emission processes probably does not involve any ‘strange’ physics but only simple gas dynamics and thermal bremsstrahlung.

This paper describes the SPICA array at Akeno, and discusses recent efforts made to improve the angular resolution of the array, concentrating on the determination of the departure of the shower front from a plane. Future research plans are also outlined.

The ground level event (GLE) observed on November 22, 1977, is of interest because of the spread of onset times observed by various cosmic ray neutron monitors. Previous reports (Fenton, Fenton and Humble 1978, 1979) have discussed this matter without being able to reach definite conclusions. We have now obtained data from a further seven neutron monitors, and also some from the Imp 8 spacecraft. These data combine to suggest that the event may have been more complex than we initially supposed.

The strong unidentified radio source 1733-565 (≡ PKS 1733-56) was chosen as a test source during the commissioning of the Molonglo Observatory Synthesis Telescope (MOST) in 1981 July. Previous radio maps have been obtained at 1410 MHz with the Parkes interferometer (Schwarz et al. 1974), at 408 MHz with the Molonglo Cross (Schilizzi & McAdam 1975) and at 1415 MHz with the Fleurs Synthesis Telescope (Christiansen et al. 1977).

We consider the effect of a velocity gradient on the source function for a spectral line formed in an atmosphere in non local thermodynamic equilibrium, a problem examined previously by Kulander and Hummer and Rybicki. A numerical method is used which extends the Feautrier technique.

The following are brief summaries of recent observational investigations of SN 1987A by ESO staff and their collaborators, which were reported at the Conference.

If computer speed and storage keeps increasing at the present rate a three dimensional numerical code modelling the exact equations governing general relativistic collapse will soon be possible; however, at present it is necessary to use simplifying approximations. Provided the general relativistic effects are limited to a ‘small’ perturbation, the post-Newtonian equations of Chandrasekhar (1965) should be adequate. These equations take the form of the Newtonian equations for a self gravitating fluid with extra terms to incorporate the 1/c 2 contributions, where c is the speed of light. The numerical solution of these equations can be achieved using any method appropriate for three dimensional Newtonian hydrodynamics.

The purpose of this paper is to advance an alternative hypothesis for the underlying distinction between solar radio bursts of spectral type V and ‘inverted U’ bursts, and to explore its implications.

We present a list of bright (< 17 mag) southern QSOs and bright (< 11 mag) stars that may be suitable for the Hubble Space Telescope link between the Hipparcos astrometric reference frame and the VLBI extragalactic frame. The QSOs have been selected from various lists of radio objects and identifications. The stars have been selected from the Strasbourg (CDS) data base and from the Preliminary Second Cape Photographic Catalogue, and supplemented with stars measured from the SERC IIIa-J Schmidt survey. The list of QSOs and stars have been included in the Hipparcos and HST schedule of observations.

A search for the 126a hydrogen recombination line, with a rest frequency of 3248.713 MHz, has been made in the 19 sources listed in Table I using the Parkes telescope. The beamwidth was 6′ are and the frequency resolution 37 kHz. In the Table RCW refers to the Rodgers, Campbell and Whiteoak Atlas, W to the Westerhout catalogue, and the co-ordinate numbers to the Parkes Catalogue of Sources. In each case the ratio of the peak of the line to the continuum TL/TC , the half-intensity width Δv and the mean radial velocity to the local standard of rest, were determined. The related velocities observed in OH emission and absorption are also shown.

The Thumbprint Nebula (TPN) in Chamaeleon (first described by Fitzgerald (1974), and shown in Figure 1) is a good example of the class of dense, dark nebulae that exhibit dark cores and bright rims, and have been referred to (Lynds 1967) as ‘bright dark nebulae’. Early observations of these nebulae established that the dust grains within them were strongly forward-scattering (Struve and Elvey 1936, Struve 1937). However, the treatment of the radiative transfer problem was too inadequate to permit more than tentative conclusions regarding the nebulae. In more recent years, with the advent of modern computers, the transfer of radiation through a dust cloud has been treated more rigorously, using Monte Carlo techniques (Mattila 1970, Witt and Stephens 1974). Witt and Stephens (1974) have demonstrated that for a dense nebula the surface brightness profile is sensitive to the dust grain density distribution within the cloud and to the scattering properties of the grains. The scattering model approach can be valuable in the investigation of very opaque dark nebulae that cannot be studied by conventional star counting techniques. This has been demonstrated in the case of the TPN by Fitzgerald et al (1976), who used the Witt and Stephens model.

It is more than 120 years since the discovery of spiral galaxies, and naturally there has been much speculation on their origin. The vital clue is the composition of the arms, and it is now known that the arms are patterns of newly formed, and hence very luminous, stars. Thus the problem of spiral arms is only part of the broader problem of the origin of stellar systems in general. The various galactic forms of the Hubble morphological classification are differentiated by their different stellar systems, and so the problem of spiral arms is part of the basic problem of the origin of the Hubble types. For this reason the potential significance of any theory of spiral arms is vastly extended.

Both Holmberg (1961) and de Vaucouleurs (1963, 1973) found a significant difference between the mean velocities of the different morphological types in the Virgo cluster of galaxies. To check on any dependence of this result upon spatial distribution, Lewis (1975) plotted the position of every object in the compilation of de Vaucouleurs (1961) as a function of its type. Figure 1 is the resulting plot for the elliptical galaxies, which appear to lie within two well-defined and well-separated groups. The principal parameters of these groups are listed in Table I. Arp (1967) briefly noted the linear form of the northern group centred on NGC 4486. This paper examines the evidence for the physical existence of these groups.

The Culgoora radioheliograph was designed in the early 1960s and commissioned in 1967. Since then there have been dramatic increases in the speed and versatility of digital integrated-circuit devices, and also a marked fall in their cost. It is now possible to replace the original signal processing electronics with equipment, based on modern digital technology, which will significantly enhance the performance of this radio telescope for solar and cosmic radio observations at metre wavelengths.

In γ-ray astronomy one often wishes to search for a periodic signal from a suspected point source. Either one knows the period in advance, for example in the case of a radio pulsar, or at least a range of possible periods, or one has no information and is searching “blind”, as in the case of SN1987a, unidentified sources in the COS-B catalogue, or binary X-ray sources without known pulse periods. In both cases one should adopt a strategy which give the best chance of obtaining a statistically significant result. The power of tests using the family of statistics based on the Rayleigh statistic is discussed for two extreme forms of possible light curves: a uniform distribution plus a delta function, and a cartoid distribution. Strategies for using these statistics are discussed. Methods of obtaining confidence bands, and in the case of an unsuccessful search, upper-limits to any pulsed component are described, and graphs given which enable these to be calculated readily given the value of the statistic obtained.

The numerical solution of the basic equations for non-linear steady convection in the weak-coupling approximation is exceedingly difficult. In astronomical applications the Rayleigh number R will be of the order of1012, and we wish to report here some results obtained in the case of high Rayleigh numbers with the use of an asymptotic method.