There exists a large number of varying methods of solution in radiative transfer theory. House and Avery have recendy published an exposition of the Monte-Carlo technique and the very nature of this solution makes it readily amenable, in theory, to the study of any transfer problem. Grant and Hunt have developed a method involving the invariant Sn matrix transformation and this also appears quite general in its application. Further, the Riccati transformation technique, developed by Rybicki and Hummer, has already been used in solving several different transfer problems. However, these methods have certain disadvantages. The equations are of first order and thus stability difficulties arise. Also, the finer details of the method rely, to a large extent, on the particular problem under consideration, and experience with such a method is required for the efficient computation of solutions.

Over the past years considerable information has been acquired concerning the structure and magnitude of sunspot magnetic fields; however, there is a paucity of data concerning the motions of the seats of these fields, i.e., individual umbrae within a spot group. The well-known effects of differential rotation cause sunspots to diverge with time in longitude at a daily rate of, at most, a few degrees per solar rotation. On the other hand, a limited number of investigations have shown that individual umbrae can have proper motions of up to 100 to 200 m/s, or about ten times greater than effects of differential rotation. In addition, equally limited observations have shown that umbrae sometimes rotate about an axis through their centre; in an extreme case the rotation reached 30°/day. The last large sunspot group of the last cycle, having Central Meridian Passage 20.5 September, 1963, has been studied by means of photoheliograms and magnetograms obtained four days before and four days after CMP at the Crimean Astrophysical Observatory. The magnetograms show the distribution of both the transverse and longitudinal components of the magnetic field in the activity region. In this study we have studied umbral motions and their relation to the magnetic field.

Frequency dependent structure is not uncommon in observations of extended radio sources. Where a source consists of two components with different spectra at an angular separation considerably less than the resolution of the telescope, the centroid position will vary systematically with frequency. A well-known example is 3C 273 though the effect in this case is quite small. With beams of a few minutes of arc, larger position differences could occur between measurements made at widely separated frequencies without the source being noticeably resolved. In a preliminary study of a sample of 120 4C radio sources, Munro and Hoskins found 17 cases of discrepancies in the range 45 to 100 seconds of arc between positions measured at 408 MHz with the Molonglo cross (beam width ~3′ arc) and at 2700 MHz with the Parkes 64 m telescope (beam width ~7′ arc) by Wills and Bolton. These separations were considered to be significant in terms of the quoted errors which were typically 10 to 15″ arc in each coordinate for both sets of measurements. It was pointed out that to explain the results on the basis of a double source model it would be necessary for the two components to differ in spectral index by ~1.

Recent reviews have demonstrated that a wide ranging selection of objects emit a major proportion of their energy at wavelengths longer than 1 µm, including such intrinsically different objects as late type stars, Be stars, F supergiants and novae. In the majority of cases the infrared radiation has been interpreted in terms of thermal radiation from a circumstellar shell of solid ‘dust’ particles. Any attempt at a detailed comparison of theoretical energy distributions with observed infrared photometry encounters the problems of uncertainties in the absolute calibration, and limited accuracy of the observations.

We discuss the expected properties of shocks in molecular clouds when the effect of a magnetic field is included. The results suggest that shocks should have magnetic precursors, and may be C-shocks rather than J-shocks, but the observations are not obviously consistent with this prediction. The effect of these shock properties on cloud collisions triggering star formation is discussed.

Large apparent superluminal velocities are observed in nuclear jets in Active Galaxies, indicating the presence of relativistic velocities almost along the line of sight. If the flow is well collimated, as suggested by the large scale radio structure, the inferred alignment leads to difficulties with source statistics. Here a modification of the usual relativistic beam model is proposed, in which the jet is assumed to contain azimuthal (swirling) flow. Perturbation analysis is used to show that the jet is unstable to a Kelvin-Helmholtz helical standing wave, the wavelength of which increases without bound in the limit of vanishing swirl. This instability may cause a cylindrical jet to follow a helical path in space, thereby reducing the implied alignment of a superluminal source, and providing a natural interpretation of non-constant superluminal velocities.

In 1988, a very powerful and versatile coudé echelle spectrograph was installed at the Anglo-Australian Telescope. Since then it has been winning about 30% of AAT time and has been highly productive scientifically. Therefore, using a coudé auxiliary telescope (CAT) to give the spectrograph more use and to free the AAT for other work is a very attractive possibility, particularly if the CAT can give a sensitivity similar to that obtained with the 3.9-metre telescope. While a conventional CAT with such performance would be very expensive, a much cheaper instrument should approach this goal, at least for high resolution spectroscopy. Even so, the cost could not be met in a reasonable time within the AAO’s budget; hence, additional international collaboration is being sought.

The Center for Astrophysical Research in Antarctica conducts various educational outreach programs as part of its mission as a National Science Foundation Science and Technology Center. The method behind the outreach programs is one of forging partnerships between Center researchers and other educational organisations. The main program serves primary and secondary students in Chicago. The core of the program is called Space Explorers and is targeted at high school students. These students attend a summer residential institute at the University of Chicago’s Yerkes Observatory. The high school Space Explorers then extend the reach of the program during the academic year by teaching in primary schools using a portable planetarium. The Center also pursues many other outreach activities and is in the process of forming an Antarctic Education Alliance.

Techniques in QED (quantum electrodynamics) have been developed previously (see for example Melrose and Parle 1983) allowing one to treat electron-photon and photon-photon interactions exactly in the magnetized vacuum and allowing one to include the effects of a medium. These techniques are extended to include particle-particle interactions. Exact cross-sections for electron-electron collisions are derived and compared with known expressions. Such calculations have application in studies of the formation and transfer of radiation in the atmospheres surrounding neutron stars.

We have detected OH maser radiation from the comet Giacobini-Zinner using the Parkes radio telescope. The emission was detected in two transitions of the ground state of OH, at an intensity consistent with the predicted OH molecular production rate. We also searched unsuccessfully for OH emission from comet Halley, from which we are able to place a significant upper limit on the intensity of OH emission.

The radio source G357.7-0.1 has commonly been regarded as a galactic supernova remnant; alternative interpretations have concentrated on the pronounced brightness gradient along its major axis. Analysis of our new map shows that this brightness gradient masks an even more crucial characteristic – symmetry about the centre – the key to a totally different interpretation.

The story of the discovery of SN 1987A by Ian Shelton and Oscar Duhalde is well known, but many other events around the time of discovery are largely unknown. I shall describe these events and some of the confusion generated on 24 February 1987.

Known Southern flare stars and RSCVn-like variables are being observed with the Molonglo Observatory Synthesis Telescope in an attempt to detect quiescent (non-flaring) emission. Two flare stars out of 7 and one RSCVn out of 8 have been detected. Quiescent emission has not been observed previously from these sources at such a low frequency. All sources so far detected have mean flux densities below 10 mJy and in at least two of them the emission varies with a time scale of about one day.

The galaxy IC4553 (Arp 220) is a peculiar galaxy having a redshift of 0.02. It has been variously described as consisting of a symbiotic pair of galaxies, as having a highly peculiar pair of nuclei, or as consisting of a nucleus bisected by a dust lane. In addition, it exhibits OH maser emission which is both the most intrinsically luminous (by four orders of magnitude) and the most distant yet detected. MERLIN observations of the continuum emission at 18 cm show a core-dominated triple structure, probably indicating jets about 500 pc in extent. The integrated OH maser emission has an identical spatial structure, but when this structure is examined as a function of frequency across the line it is found that each spatial component has its greatest intensity at a different frequency. This is interpreted as amplification of the radio continuum image by the OH masers. The change in spatial structure across the emission line is caused by the velocity structure of the OH gas. Measurements of the velocities of these masers therefore reveal the kinematics of the central part of the galaxy. Optical and infrared observations indicate that at the centre of the galaxy is a Seyfertlike active galactic nucleus, which appears double on optical plates only because of the dense dust lane which bisects the nuclear region. This indicates that IC4553 is an edge-on Seyfertlike galaxy. The OH maser radiation is a result of stimulation of the OH along the line of sight within the galactic plane by the strong far-infrared radiation from the nucleus. No abnormal conditions are required for this process, so IC4553 may not be unique, and we should search for OH maser emission in other edge-on active galaxies.

The angular diameter of a star, combined with observed stellar fluxes in absolute units, allows the absolute fluxes emitted at the surface of the star to be calculated and thus provides a stringent test of model atmosphere predictions. Furthermore, if the flux distribution is observed at all wavelengths contributing significantly to the net flux, an empirical effective temperature can be found. Sufficient data are now available for Sirius (αCMa) to be studied in this way.

Evidence has recently been put forward that Jupiter might be modulating the intensity of cosmic radiation observed at the earth (Pizzella and Venditti 1973; Cini-Castagnoli et al. 1973). It therefore seemed worthwhile to analyse underground meson data in Jovian time for any evidence of an effect at the higher energies over a complete orbital period.