Operation of the six 13.7 m antennas of the Fleurs synthesis telescope as a sub-array has provided a new and surprisingly versatile astronomical tool. With enhanced reliability and fully automated operation, unattended observing over several days is possible. Interleaved ‘multiple-snapshot’ observations of many fields per day can be made.

The array has shown itself to be particularly suitable for the measurement of precision (a few arcsecond) positions for the optical identification of a large number of radio sources, a survey of compact sources and the monitoring of the activity of several radio stars over periods of weeks. At present a program of recalibration is under way to improve the positional accuracy and dynamic range of the instrument.

The accepted interpretation of the low frequency turnovers in the spectra of many extragalactic radio sources is that they are due to the effects of synchrotron self-absorption, i.e. to the source becoming optically thick. It has been shown that the signs of the degrees of both linear and circular polarization for a homogeneous source at frequencies where it is optically thick are opposite to those at frequencies where it is optically thin.

An analysis of 1973 RT Andromedae B and V light curves is presented. The results are fitted into a spot evolution sequence found in a previous study which used the same technique on different data. The new values of the system’s physical parameters are in general agreement with the earlier ones.

The astrophysical literature contains many discussions on exactly which changes in a star’s structure are responsible for the extremely large radii found after core hydrogen exhaustion. Different authors favour different mechanisms. Unfortunately none of the proposals are easily verified nor are they easily disproven. In this paper we examine the suggestion that it is the increased central mass concentration (i.e., the growth of the hydrogen exhausted core) which is the primary agent responsible for envelope growth.

The literature contains numerous predictions of an X-ray pulse associated with the emergence of the shock-wave at the surface of a star undergoing a supernova explosion. Applied to supernova 1987a, these suggest a small, solar-flare like event lasting about a minute with a terrestrial flux of order 1 μWm-2 and a black-body temperature between 106K and 107K occurring between 0900 and 1000 UT on February 23, 1987. Unfortunately, no direct X-ray observations appear to have been made. However, such an event would be expected to give rise to an observable enhancement of ionization in the upper D-region of the ionosphere. The absence of a detectable perturbation in VLF radio signals propagating in the earth-ionosphere waveguide sets upper limits to the X-ray flux and temperature below those predicted.

We study the radio power of the core and its relation to the optical properties of the host galaxy in samples of high-excitation (HERG) and low-excitation (LERG) Fanaroff–Riley type II (FRII) radio galaxies. The radio galaxy sample is divided into two groups of core/non-core FRII, based on the existence of strong, weak or lack of single radio core component. We show that FRII LERGs with radio emission of the core have significantly higher [O III] line luminosities compared to the non-core LERG FRIIs. There is no significant difference between the hosts of the core and non-core FRIIs of LERG type in galaxy sizes, concentration indices, star formation rates, 4000-Å break strengths, colours, black hole masses, and black hole to stellar masses. We show that the results are not biased by the stellar masses, redshifts, and angular sizes of the radio galaxies. We argue that the detection of higher [O III] luminosities in the core FRIIs may indicate the presence of higher amounts of gas, very close to the active galactic nuclei (AGN) nucleus in the core FRIIs compared to the non-core FRIIs or may result from the interaction of the radio jets with this gas. The core and non-core FRIIs of the HERG type show no significant differences perhaps due to our small sample size. The effect of relativistic beaming on the radio luminosities and the contribution of restating AGN activity have also been considered.

The authors discuss the light-pollution prevention ordinance passed by the Japanese town of Bisei in 1989.

NGC 6302 is one of the highest excitation planetary nebulae known. It has an obscured central star with a temperature estimated at 430,000 K. We present here CCD images in Hα and Hβ of NGC 6302, and interpret the differences between the images as being due to extinction caused by dust within the nebula. The dust appears to be concentrated in the core, as expected from infrared observations. There is no evidence of patchy foreground extinction, although there is a slight difference in the average extinction between the eastern and western lobes of the nebula. A comparison between the Hα image and a 5 GHz map gives a dust extinction of ΔAV~3.5 to the central star. The outer contours of the 5 GHz map are not in good agreement with the optical images, and further observations at this frequency would be useful.

We have deduced the yearly averaged value of the solar diurnal variation as observed by a surface muon telescope and three underground muon telescopes over the years 1957 to 1985. This has allowed us to examine the temporal variation in both the latitudinal gradient Gz and the product of the parallel mean free path and the radial gradient of galactic cosmic rays during three consecutive solar cycles. The median rigidities of the primary particles being detected by the telescopes are 50 GV in the case of the surface muon telescope and greater than 150 GV in the case of the underground muon telescopes. We have compared our results with those of a similar study made from observations of the solar diurnal variation by neutron monitors and an ion chamber, which have median rigidities of response between 17 and 70 GV (Bieber and Chen 1991a). The product has a solar magnetic cycle dependence and our values are lower than those observed by neutron monitors, in agreement with the Bieber and Chen observation that reverses after a solar magnetic field reversal, in accordance with drift theories.

Recent observations with the Australia Telescope Compact Array show that the elliptical galaxy NGC 5266 has a disk of neutral hydrogen extending to almost 10Re. This HI disk lies along the galaxy’s major axis, at right angles to the inner minor-axis dust lane. The geometry and kinematics of the gas will allow us to determine both the intrinsic shape of the stellar galaxy and the mass distribution. The mass-to-light ratio M/LB rises from about 2 in the central regions to ~12 at 9Re (H0 = 50km s−1 Mpc−1).

One of the quantities usually required when solving the equation of radiative transfer is the intensity of radiation emerging from the surface of the medium under consideration. For multi-dimensional situations however, the methods presented to date have been numerical, and these first calculate the so-called source function Sv (r, Ω) as a function of position r, angle Ω and frequency v. This is generally the most difficult part of the exercise since an integro-difierential equation must be solved. The emergent intensity is then determined by solving a relatively simple first order differential equation by any of the well known numerical integration schemes. However, if the emergent intensity is required at a large number of angles, frequencies, and positions on the surface of the medium, and this is usually the case, the amount of computing needed may be considerable.

Over the past ten years a comprehensive educational program has been developed at Carter Observatory which covers every level from pre-school to PhD. A great deal of time also is expended in a varied adult education program. Every effort has been made to co-ordinate the various parts of the program in such a way that people will be encouraged to take a productive interest in astronomy.

The spectrum of a symbiotic star consists of an M-type absorption spectrum, a B-type shell spectrum and nebula emission lines, the relative contributions of these three components varying with time. The light curves of the symbiotic stars vary with a semi-regular period typically 200-800 days while larger eruptions occur on a timescale of ~ 3.5 years. Some suggestions which have been advanced to explain the combination spectrum, variability and eruptive behaviour of the symbiotic stars are:

1. (a) the symbiotic stars are binaries consisting of a hot and cool component.

2. (b) the symbiotic stars consist of a single hot star surrounded by a large optically thick envelope giving the appearance of a hot continuum with the absorption spectrum of a cool star superimposed on it.

3. (c) the symbiotic stars are single stars surrounded by a shock wave heated chromosphere.

   Although some of the symbiotic stars are undoubtedly binaries (for example, T Coronae Borealis), observatienal evidence suggests that others may be explained by hypothesis (c) above. The calculations described below provide an explanation of the symbiotic stars in conjunction with hypothesis (c).

The existence of red supergiants such as those in the clusters h and χ Persei has puzzled stellar evolution theoreticians for some time. Suggested explanations for them have included stars in a stage of gravitational contraction to the main sequence, or between nuclear burnings, core helium burning stars, and stars burning carbon or oxygen in the core, but it is now generally accepted that most red supergiants are core helium burning stars.

This paper discusses the role of the planetarium as an indispensable means of teaching astronomy and as an increasingly popular way of teaching science.

Plasma loops are the dominant structures, in the higher levels of the Sun’s atmosphere above active regions. Much of our knowledge of their properties has come from space observations made over the past decade or so in the EUV and X-ray regions of the spectrum and, more recently, from high-resolution, two-dimensional images of microwave sources obtained with the Very Large Array radio interferometer (VLA). On the other hand, the spatial resolution of rocket and satellite observations has so far generally failed to match that of ground-level optical observations made in Hα and other strong chromospheric lines. The latter permit one to study in much greater detail the morphology of individual loops, as illustrated for example in the recent work of Loughhead, Wang and Blows (1983). These authors addressed themselves to the task of determining the true geometrical shapes of individual loops, a problem which had hitherto received little attention.

Magnetic fields of about 1012 G have now been measured in several astrophysical objects (Trümper etal. 1978, Wheaton et al. 1979, Mazets et al. 1981). In the case of pulsating X-ray sources, the presence of a companion star indicates that accretion is probably the energy source for the X-rays.

Although the approximately flat rotation curves of gas in the outskirts of spirals are generally taken as strong evidence for spherical, isothermal dark matter halos, this conclusion is often incorrect and always model-dependent. A re-examination of the old and (nearly) model-independent inversion technique for determining the surface mass density of galaxies from their kinematics is presented. The method is shown to be relatively insensitive to noise in the kinematics. Due to incomplete kinematical knowledge at large radius, however, the surface mass density is reliable only in the inner half of the galaxy, a result that also applies to traditional rotation curve fitting techniques.

The bright radio emission from flare stars has three characteristic properties: high brightness temperature, high degree of circular polarisation and rapid temporal variations. Two proposed emission mechanisms, electron cyclotron maser emission (ECME) and plasma emission, are compared and contrasted. It is argued that although the important features of the emission can be explained in terms of either ECME or plasma emission, all three favor ECME. However, the escapes of the radiation through the second harmonic absorption layer remains inadequately understood, and as a consequence doubts about the ECME interpretation remain.

Although transient decreases in cosmic ray intensity of the type first reported by Forbush (1937) have been observed and studied for more than 40 years using a variety of detectors at many locations, from medium depths underground to those on spacecraft far from Earth, the precise nature of the physical process causing these events is not yet clear (see, for example, McKibben 1981).