The accurate determination of radio source positions is one of the principal uses of high resolution instruments such as the Molonglo Radio Telescope. A critical stage in this process familiar to all radio astronomers involves the measurement of the instrumental response pattern relative to some accurate time or position marker. Ideally, the analysis procedure should introduce no further errors either random or systematic beyond those which are already present in the data. This is virtually impossible with chart analysis.

Whether a mechanism for the emission of radiation can properly be regarded as thermal or non-thermal depends on the nature and extent of the interactions that take place between the radiation resulting from such a process and the surrounding medium. Thus, no matter what the emission mechanism there can be a balance between emission and absorption processes such as to produce a state of local thermodynamic equilibrium (LTE), so that the net radiation available for transport through the source region is thermal.

A comprehensive study of the anisotropy (i.e. streaming) of solar cosmic rays at energies ~10 MeV revealed two distinct types (McCracken). The first occurs during onset phase of the event, is large (> 20%), and is really the flow of cosmic rays along lines of force driven by a density gradient. The second describes the decay of the event, is small (10%), and indicates a flow radially away from the Sun.

A photometric survey of a central region of the LMC has been undertaken to obtain a magnitude and colour limited sample of bright asymptotic giant branch (AGB) stars; the stars were selected from V and Ic plates taken by the UK Schmidt Telescope Unit (UKSTU) at Coonabarabran. Infrared JHK photometry has been obtained for all the stars in the sample in order to determine bolometric magnitudes, and spectra have been obtained for most of the stars to obtain spectral types. Stars in the sample have bolometric magnitudes up to the AGB limit of Mbol ∼ – 7.1, and many of the stars show evidence for dredge-up of carbon and s-process elements during helium shell flashes. A bolometric luminosity function has been constructed and its behaviour is discussed in terms of possible mass loss scenarios.

This is the second of a series of papers presenting detailed optical spectra for QSOs and strong-emission-line galaxies identified with radio sources from a selected area (−15° to −23° in declination) of the Molonglo Reference Catalogue (MRC: Large et al. 1981). The catalogue is complete to 1 Jy at 408 MHz although it contains many weaker sources. First results were reported by Hunstead et al. (1978, Paper I) and a summary was given by Hunstead (1979). Results have also been given by White et al. (1980) for spectra of QSOs identified with radio sources to a much deeper level of 88 mJy from a small strip within the larger selected area.

The high radio positional accuracy now being achieved with long baseline interferometers, aperture-synthesis instruments and large filled-aperture telescopes makes the rapid and reliable processing of optical identifications essential. For some time now the customary approach for large surveys has been to carry out a search for possible radio-optical associations using the prints of the Palomar Sky Survey. Rough positions for optical counterparts have generally been estimated by interpolation within a small grid centred on the radio position. However, the final confirmation or rejection of the identifications has awaited spectroscopic or accurate positional data from one of the large optical telescopes, usually the 48-inch Schmidt or 200-inch reflector at Mt Palomar. It is becoming increasingly evident that not only is this process rather slow but it also means that preliminary interpretive work dealing with the identification content of a radio survey will be necessarily limited in scope.

We discuss the appearance of solar active regions as seen in EUV line radiation in terms of a system of simple static coronal loop models. The loop models are based on those of Rosner et al. (1978) and may be understood in terms of the scaling laws introduced by these authors. We present here some generalized scaling laws which demonstrate that the global properties of loops in fixed length are insensitive to everything but the overall heating rate or the basal pressure. The model and scaling laws appear to describe hot loops (T< 106K) well. Empirically determined temperatures and densities in cooler loops are not in agreement with coronal loop models.

We have computed a simple model of an active region using a dipole magnetic structure. The individual loop structures were calculated on the basis of the two different assumptions of constant basal pressure and of constant heating rate. This paper presents a preliminary discussion of the results and a comparison with observation.

We have carried out calculations to model the hydrogen emission line spectrum of intermediate polars with accretion disks. We show that we can explain most of the observed optical continuum and line fluxes in terms of hard and soft X-rays that originate from the accretion shocks and are reprocessed in curtains formed by magnetically channelled material.

It is believed that the splitting of the SMC into two fragments and the production of the Inter-Cloud gas and the Magellanic Stream occurred in the one event 4 × 108 years ago. This event was a collision between the LMC and SMC. This time is too short for the Stream to be tidal, or be the result of stripping of the Inter-Cloud gas by a diffuse gaseous halo. It is proposed that the clouds in the Stream are the results of collisions between the Inter-Cloud gas and HVCs in the Galactic halo. A model of this process accounts for all of the observational features of the Stream. Observations of HVCs in the path of the Magellanic Clouds are used to predict the development of the Stream. The HVCs in our halo are thought to be a result of a collision of a galaxy with our Galaxy 6 × 109 years ago.

A substantial population of red quasars has been discovered in a complete sample of flat-spectrum radio sources. Dust is the most likely cause of the reddening in this sample. The location of the dust is poorly known, but may either be in the line-of-sight to the quasar, or in the immediate quasar environment. In this paper we are interested in models where the dust is located in the line of sight to the quasar. We calculate the probability distribution of the optical depth in galactic dust as a function of source redshift, using a range of parameters which might describe real galaxies. We compare these results with those found for our sample of radio quasars. If the dust content is unevolving, then it is not possible to account for all the observed reddening in the quasar sample using these models. Our minimum dust model predicts that 15% of background quasars to z ~ 5 will have a line of sight within 5 kpc of a galaxy’s centre, and would therefore be reddened out of B-band flux-limited samples.

Theoretical Hα profiles have been used by Rodgers and Bell (hereafter denoted by RB) to obtain the effective temperatures of several cepheid variable stars. They find that the profiles are sufficiently sensitive to temperature to enable them to determine temperatures which are accurate to within about 300°, while being insensitive to other factors such as gravity or the form of the temperature distribution in the model atmosphere.

Some initial results of a flux-calibrated CCD Hα imaging program of bright, nearby southern spiral galaxies are presented. Very few southern hemisphere spiral galaxies have ever been completely imaged in Hα, let alone with a CCD. This survey (which mainly uses the MSSSO 1.0-m reflector with an f/3.5 focal reducer) will, when combined with spectrophotometry of the H II regions thus revealed, allow us to trace the chemical evolution of each galaxy. Furthermore, since the absolute Hα flux is a reliable measure of the high-mass star formation rate in a galaxy, such observational data will permit us to test the predictions of the various star formation theories.

A 3 GHz maser from the Onsala Space Observatory, Sweden, is currently at Parkes on a long-term loan basis. So far, it has been used on the 64-m radio telescope for a two-week period of spectral-line observations in February 1979, providing a system sensitivity far superior to that previously available at the same frequency. The observed lines were the ground-state transitions of CH at 3264, 3335 and 3349 MHz, the 211 – 212 transition of H2CS at 3139 MHz, and the 211-212 transition of CH3CHO at 3195 MHz.

Photometric observations on the UBV system have been made of a number of optically identified radio sources. The measurements are basically of two types: (1) offset photometry with the Siding Spring 40-inch reflector of objects identified as probable quasars or N galaxies, and (2) observations with the Siding Spring 24-inch reflector of radio galaxies brighter than V = 14m.0.

My lecture this evening is dedicated to my late friend and fellow astronomer, Harley Wood, who died on 26 June 1984 at the age of 72. It is a fine thing that the ASA has decided to give the name of Harley Wood to an annual public lecture at the time of the society’s Annual General Meeting. For besides making a monumental contribution to the astrometry of the southern skies, Harley became a leader, a kind of organizer and father figure, among Australian astronomers. He played a leading part in the formation of this society and was its foundation President. He will also be specially remembered by a small group of us, about half a dozen, who met regularly in the charming old building of Sydney Observatory to plan the 1973 IAU General Assembly held in Sydney, the first time ever in Australia. Harley chaired not only the local organizing committee, but the ladies’ committee too. My wife still recalls the gentle, but firm way in which Harley once admonished her for addressing a remark across the table without going through the Chair. Harley was totally approachable and totally positive at all times: you could always count on his support for any sensible initiative. He had many friends and no enemies that I have heard of. And unlike so many of his profession, there was no hint of the egotist or the prima donna. I count it a privilege to have been his contemporary and colleague.

We have detected a large cold HI cloud consisting of several fragments in the region south of the Chamaeleon I dark cloud. The cold HI cloud is shown to be a future site of star formation.

The use of artificial neural networks (ANNs) as a classifier of digital spectra is investigated. Using both simulated and real data, it is shown that neural networks can be trained to discriminate between the spectra of different classes of active galactic nucleus (AGN) with realistic sample sizes and signal-to-noise ratios. By working in the Fourier domain, neural nets can classify objects without knowledge of their redshifts.

Transit observations of the Sun can be made with the Molonglo radio telescope which is now in full operation at 408 MHz. Thus the Sun can be scanned once per day by eleven separate beams evenly spaced in declination. Because of foreshortening of the north-south arm with increasing zenith angle, the total coverage varies and in winter about 28′ arc can be covered by the eleven beams, whereas only 15′ is covered in mid-summer. This also means that the beamwidth in declination changes from 2′.9 at the zenith to about 5′.8 for the mid-winter sun. The beam is 2′.8 wide in right ascension. A further complication is the fact that the positions of the eleven beams cannot be chosen arbitrarily but can only be selected from a predetermined set of beam positions. These latter have been fixed by the phasing connections built into the telescope and cannot be changed easily. Hence for all the above reasons the strip of Sun which can be scanned will vary from day to day.