The eighth magnitude star HD 101065 is an extremely peculiar star with a unique spectrum characterized by numerous strong lines of the rare earths and the absence, or at least a remarkable weakening, of the lines of the iron group (Cowley et al. 1977). Besides the lanthanides only yttrium, zirconium, calcium and barium are definitely present in the atmosphere in substantial quantities. The evidence for the presence of lithium and strontium is subject to some doubt since these elements are represented only by one or two reasonably strong lines, which is insufficient for a positive identification in a spectrum as complex as that of HD 101065. The evidence for the presence of other elements is the subject of a critical examination in a recent paper by Cowley et al. (1977). The effective temperature of the star is about 6100 K (Przybylski, 1977) which is substantially lower than the temperature of any known Ap star. However, the effective temperature of HD 101065 is still subject to controversy (Wegner, 1976).

Sites of recent star formation often radiate strong maser emission from methanol transitions near 6-6 and 12 GHz. We have studied many of these masers over several years and find that intensity variations are common on both transitions. We present observations which demonstrate marked variability in 48 sources. We explore the characteristics of the variability and find it to be typically quasi-periodic, on a timescale of between a month and several years. The amplitude of the variation is most commonly less than a factor of two, but can reach factors of ten. The variability of different features in a source is usually independent. Variability of features seen at both 6·6 and 12 GHz is sometimes correlated, with larger amplitudes usually seen at 12 GHz. A likely inference is that variations are occasionally due to a change in the pump rate throughout the masing region, but most are consistent with a change in the masing path length due to large-scale motions. In addition, it is likely that the majority of 6·6-GHz masers are saturated whereas the 12-GHz masers may be somewhat less saturated.

The structure of small diameter radio sources can be investigated by studying the scintillation of the source due to the interplanetary medium when the line of sight approaches the Sun. Observations of radio source scintillation are currently being undertaken with the separate arms of the 1 mile radio telescope at the Molonglo Observatory. The EW arm allows successive transit observations with three fan beams, 1′.4 EW by 4°.2 NS at 408 MHz, bandwidth 2.5 MHz. Sources transit the half-power points of each beam in 6 sec δ seconds of time (δ is the source declination). The NS arm gives eleven fan beams at neighbouring declination, 1′.5 sec Z NS by 4° EW (Z is the zenith angle). Complete transit of a NS beam takes 15 sec δ minutes.

In the preceding paper, observations of the coronal broadening of the Crab Nebula during 1969-71 were described. The basic parameters, radial and tangential broadening, and their relation to previous work were discussed. Whereas previous observations have utilized two or three interferometers only, so that the degree of broadening along any particular axis could only be obtained under the assumption of a particular form (e.g. Gaussian) for the angular power spectrum, the present work has enabled complete sampling of the two-dimensional brightness distribution of the broadened source. It is therefore possible, and of considerable interest, to compare the observed distributions to those computed on the basis of various theoretical models for the scattering process.

Observations of the galactic background radio emission at a number of frequencies between 2.7 MHz and 1.07 MHz were made in association with the plasma depletion experiments of Spacelab-2 to test the concept of making low frequency radio observations through an artificial ionospheric window. Following the Shuttle OMS burn at a time when foF2 was 1.99 MHz, a decrease in the maximum ionospheric electron density of approximately 30% occurred. The first observations of the radio emission at high galactic latitudes with good angular resolution (25 degrees) were obtained during this event.

Most if not all metre-wave Type III bursts appear to be associated with solar active regions (e.g. Duncan 1977). There is a well-known association of Type III bursts and flares within a few minutes of the onset of the brightenings seen in Hα (Wild et al. 1954). Early descriptions of these observations were given by Malville (1961) (or see Kundu (1965) for review). More recently Jackson et al. (1978) have reported the occurrence of a broad maximum of Type III bursts 10 to 5 h prior to mass ejection transients seen by the white light coronagraph on Skylab.

The 3 mm radio continuum emission from active galaxies consists of three components:

1. (1) Synchrotron emission from the active galactic nucleus (AGN), which is over 1 Jy in 3C273 but which is not significant in most of the types of galaxy considered here.

2. (2) Free–free emission from H II regions. The flux of this in a starburst galaxy is typically of the order of 10 mJy and could be imaged with a 3 mm-capable Australia Telescope Compact Array (ATCA).

3. (3) Emission from the tail of the 50–100 K black-body spectrum of the dust. For example, the dust in Arp 220 (redshift of 0·02) at a temperature of 50 K has a flux of 30 mJy at 3 mm. Interestingly, this flux does not decrease substantially with redshift, as the decrease in brightness is compensated for by the redshifting of the steep edge of the blackbody curve, and so infrared-bright galaxies can be studied up to high redshifts with existing instruments.

Relative efficiencies for the discovery of Earth-crossing asteroids (ECAs) are modelled for various telescopes at Siding Spring. It is found that the narrow-field instruments—the Anglo-Australian Telescope and the 40 in and 2·3m reflectors—are not competitive in this regard for present CCD imaging systems. The UK Schmidt Telescope (UKST), if used to take short-exposure stereo pairs of photographs, would be an effective search tool, outperforming all current systems apart from the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) systems now being implemented by the US Air Force for ECA searches. If a CCD mosaic were fitted to the UKST, its performance would far exceed that of any other device at Siding Spring, and it would produce ECA discoveries at a rate around 3–4 times as high as GEODSS, but at considerable expense. The most sophisticated search instrument currently in use is the University of Arizona’s Spacewatch telescope; a notable result found here is that even with its present CCD, the Automated Patrol Telescope (APT) of the University of New South Wales would be able to match or outperform Spacewatch for all ECA sizes, including ~10m objects, should this modelling be a reasonable representation of its real performance. In terms of cost-effectiveness and telescope availability, the conclusion arrived at herein is that the APT, equipped with small-pixel but large-format CCD chips of high quantum efficiency, would be an extremely effective ECA search instrument: if operated with 12 μm pixel chips covering a 4° × 4° field it might produce ECA discoveries at a rate well in excess of the combined rate for all current search programs.

Conditions on the high Antarctic Plateau would appear to be extremely favourable for a wide range of astronomical research. Before a decision can be made on constructing an observatory, data are required on site conditions at the most promising locations. To enable these data to be collected, a Lockheed Automated Geophysical Observatory is being purchased. This facility will be fitted with a suite of astronomical site-testing instruments, and deployed to several sites on the Antarctic Plateau. This program will allow a definitive assessment of the site conditions to be made by the end of this century.

As part of a program to investigate southern extragalactic radio sources, the Molonglo Reference Catalogue source 1452-517 has been observed with, the MOST and FST. It was found to have a compact core and broad lobes giving an angular size of around 20 arcmin. Despite the low galactic latitude (b = 6°) a probable identification has been made with a magnitude 18 galaxy indicating a physical size of over 1 Mpc.

Local large scale structure is best studied using statistically complete samples which cover the entire sky, and for which full redshift information is available. The optical galaxy redshift surveys which have been made to date involve many thousands of objects but cover only limited parts of the sky, and so provide only a fragmented picture of local large scale structure. Complete samples of radio and X-ray galaxies are available, however, with large sky coverage. While the number of objects is small, they may still suffice to define the dominant local structures, particularly as they may preferentially sample the deeper gravitational potentials and so provide a more efficient tracer of dominant structure.

Last year I described pairs of spherical mirrors that remove the coma and astigmatism in the image formed by a paraboloid mirror and leave the spherical aberration corrected. The investigation can be extended to deal with other shapes of primary mirror, for example the hyperboloid primary of the Anglo-Australian Telescope. The algebraic analysis becomes more complicated than for a paraboloid; but it still has the feature that at an early stage a cubic equation has to be solved, each real root of which gives rise to a second cubic. Thus in principle the mathematics could lead to nine solutions. However, it again turns out that not all the roots are real; and even for the real roots not all the solutions are physically useful, because in some cases the final image is virtual, and in others the tertiary mirror lies behind the secondary where light can not reach it. When the primary is a paraboloid, there are three useable solutions all with the property that the field corrector (consisting of the pair of spherical mirrors) can simply be scaled up or down at the user’s pleasure according to the diameter of the field he wishes to photograph. When the primary is of any other shape this is no longer possible.

Some while ago (Prentice 1973a) I demonstrated that if the present Sun were to possess a small burnt out central core of mass 2-3% M ⊙ its neutrino flux would be a factor 10 or so smaller than that of conventional homogeneously evolved solar models. It was not, however, conclusively shown what conditions might lead to the formation of such a core or indeed whether a burnt out core could be attained after 4.7 × 109 yr. of nuclear evolution. In this connection Demarque et al. (1973) has considered the evolution of an initially inhomogeneous model consisting of a hydrogen free core surrounded by a homogeneous envelope.

Ground-based gamma-ray astronomy has slowly developed over the past quarter of a century to a position now where a number of sources are known to produce gamma-rays in the energy range 1011eV to 1018eV. The observations are difficult, with exceptional signal to noise problems, but improved techniques are now allowing observers to proceed with confidence. In this paper the physical bases of the observations are emphasised to show the important issues in the field and the present state of the observations is indicated.

The cataclysmic variables are close binary systems consisting of a late type star and a collapsed star, usually a white dwarf, undergoing mass exchange. According to the standard model, the late type star (the secondary) fills its Roche lobe and material escaping from the inner Lagrangian point is transferred to the primary by means of a mass transfer stream and an accretion disc. The spectroscopic and photometric properties of most cataclysmic variables can be understood in terms of radiation from the various components of such a system, with the accretion disc usually dominating in the optical region (see Warner (1976) for a review). However, recently a new class of cataclysmic variables has been discovered with distinctive optical properties that are inexplicable in terms of the standard model. These systems known as the AM Herculis type variables have provided the first direct evidence for the presence of strong magnetic fields in the white dwarfs of some cataclysmic variables. We present here a review of some of the important properties of these variables with emphasis on the unique system VV Puppis which has provided the first unequivocal evidence for high harmonic cyclotron radiation from white dwarfs.