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.

Observations of the Pluto-Charon system using the Hubble Space Telescope are soon to provide another test of the modern Laplacian theory of solar system origin. According to this theory, Pluto, Charon and Neptune’s moon Triton are condensed remnants of the gas ring which was shed by the proto-solar cloud at Neptune’s orbit, and from which Neptune formed. Each body should have the same bulk chemical composition provided that the influence of secondary events such as physical collision can be neglected. Here we report a model for the time-dependent, surface-catalysed production of CH4, solid carbon C(s) and CO2 within the outer layers of the proto-solar cloud. This model is used to determine the condensate mix which best fits the Voyager 2 spacecraft measurements of Triton’s mean density. We suggest that Triton is a chemically homogeneous structure consisting, by mass, of 44.2% anhydrous rock, 2.1% graphite, 33.0% water ice and 20.7% dry ice (i.e., solid CO2 ice, of which a fraction nearly 2/3 is present as the clathrate hydrate CO2·5.75 H2O). On the basis of this composition, the individual mean densities of Pluto and Charon are predicted to be 2.02 ± 0.02 g/cm3 and 1.94 ± 0.02 g/cm3, respectively, assuming a mean surface temperature of 35 K. The mean density of the combined system is predicted to be 2.01 ± 0.02 g/cm3.

Ring-width time series obtained from Engelmann Spruce trees growing at high altitude sites in the Rocky Mountains, Colorado, exhibit dominant 11-year spectral periodicities. A significant linear cross-correlation also exists between these series and the Zurich series of annual sunspot numbers. A regression model based on these proxy data has been developed for the annual variation of the 11-year solar cycle. It is established that over the calibration period a very high percentage of the variance (40%) in growth patterns, contributed by a single source, can be explained by solar variation. The model correlates with the Zürich series of sunspot numbers at the 99% significance level post 1870 AD. However, over the total period 1700–1870 AD the comparison was found to be not statistically significant at lag 0. Some possible reasons for this are considered.

The availability of Magellan radar images of Venus on CDROM allows small research groups to engage in planetary physics projects using simple image processing systems. The material lends itself to short projects for high school students or Masters students.

Our initial investigations using the Magellan data have evolved into a Masters project which concentrates on the morphology of small scale structures which have terrestrial counterparts. These include studies of volcanic cone fields, lava tubes and other collapse features, and impact features.

Our current understanding of Herbig-Haro objects and their relationship with outflows and Pre-Main-Sequence objects is limited. Although the general mechanism of outflows is understood, the detailed questions concerning the outflowing material’s origin and the collimation mechanisms remain largely unanswered. The role of multi-waveband observations (visible, infrared and radio) is vital to our understanding of the shock dynamics of outflows.

This paper discusses high spatial resolution near infrared maps of three outflow complexes, HH34, HH46/HH47 and HH54, made using the Anglo Australian Observatory’s infrared camera, IRIS. For the first time molecular hydrogen emission is observed associated with the edges of outflow cavities. In the cases of HH46/47 and to a lesser extent HH34 molecular emission is seen coincident with highly collimated jets feeding the outflow cavities.

The low-mass X-ray binary source Cyg X–3 has been extensively observed from radio to ultra-high-energy (UHE) gamma-ray energies (i.e., energies >1015eV). In the radio, Cyg X–3 exhibits intense non-thermal outbursts (flares) and a double-sided relativistic jet morphology. Interestingly, at energies above 1 TeV (1012eV), the gamma-ray emission is highly variable and possibly correlated with the radio outbursts. This emission results primarily from the radiative decay of π°-mesons generated in inelastic collisions between relativistic nuclei (predominantly protons) and the surrounding matter. The observed flux of UHE gamma-rays from Cyg X–3 implies that Cyg X–3 is a localised accelerator of such particles.

We propose a model of Cyg X–3 wherein particles expelled by the source are accelerated by Shockwaves in the relativistically expanding jets. Intense flaring episodes then lead to time variations in the ambient particle flux which account for the observed features at UHE energies.

During the solar maximum of 1989–91 an unprecedented sequence of 13 cosmic ray ground-level enhancements (GLEs) was observed by the world-wide neutron monitor network. Of particular interest were two GLEs observed by the Australian network. The 1989 September 29 event was the largest GLE in the space era while the October 22 GLE included an highly anisotropic precursor peak.

Analysis of both these GLEs, taking into account disturbed geomagnetic conditions, shows that the particle arrivals at the earth were unusual. The September 29 GLE had significant particle propagation in the reverse direction and as the particle flux decreased following the peak the spectrum also softened. In contrast, the 1989 October 22 precursor exhibited extreme anisotropy while the particles involved in the main GLE showed a complex temporal structure possibly indicating multiple particle injection at the solar acceleration region.

The transfer of kinetic energy between cosmic rays and charged dust grains is investigated. The time required for heating of the dust grains due to Coulomb interactions is estimated and compared with the heating time due to ionisation losses by the cosmic rays. Heating of dust grains by cosmic rays is examined in connection with the FIR–radio correlation in galaxies: even for the most favorable conditions, including a high energy density in low-energy, ≲ 100 keV, cosmic rays, the conclusions are equivocal.

Diffusive shock acceleration produces a power law momentum distribution f(p)α p−b, with b ≥ 4 for a single shock, and b = 4 for a single strong shock. It has been shown that the distribution for acceleration at a sequence of identical shocks is flatter, approaching f(p)α p−3 below a high energy knee, for an arbitrarily large number of shocks. We show how this flatter distribution arises and discuss the range of momenta over which it extends after a finite number of shocks.

A fully-steerable 3.7 metre radiotelescope has been developed as an aid to undergraduate teaching. By using commercially available domestic satellite television components, excellent performance can be achieved at very low cost. The telescope is to be fully computer controlled, and has interchangeable feed horns and low-noise amplifiers for 21 cm, 2.5 cm and 7.5 cm. Experiments will include measurement of the surface temperature of the moon and Venus and of the effective temperature of the sun, plus observation of the brightest thermal and non-thermal galactic sources.

This paper evaluates the COSMOS database as a tool for large-scale automated optical identification programs. Firstly, we explore the limitations inherent in the database by a study of regions centred on clusters of galaxies. We then perform an automated search in the database for a sample of previously measured optical objects and compare the properties of corresponding objects. Finally, we describe a set of new plotting routines in AIPS (Astronomical Image Processing System) designed to plot COSMOS-derived ellipses and, optionally, magnitudes onto radio images.

High resolution imaging at radio frequencies has revealed several long, filamentary, non-thermal sources in the Galactic Centre region. One of these, known as the Snake, is unique in that it lies outside the Galactic Centre Lobe, and has two kinks along its length, one of which appears to be associated with a small, resolved source. For this work the Snake is assumed to be embedded in a region where both the magnetic field and the particle energy spectrum are uniform. The Snake is then modelled as an enhancement over the background of the particle energy spectrum. Some preliminary results from this model are presented here.

The Parkes radio telescope has been used to search a list of small, dense southern dark clouds and Bok globules for ammonia emission at 23.7 GHz. The ammonia observations, together with IRAS data and the cloud’s visual appearance, have been used to determine a short list of dark clouds for observation with the infrared imaging system (IRIS) on the Anglo-Australian Telescope, in an attempt to determine the dust density distribution within the clouds. Near-infrared images of a number of the short listed clouds have been obtained with IRIS at J, H and K’. Preliminary results are reported for this ammonia survey, together with IRIS images of the strong ammonia source DC 297.7–2.8. Coincident with the dense ammonia core of this object is an IRAS ‘core’ source, IRAS 11590–6452 and an extremely interesting near-infrared source, which lies on the edge of the error ellipse of the IRAS source.

Molecular ices are a common component of the dust in many molecular clouds and circumstellar shells. The most abundant molecule, H2O, has several infrared spectral features which have strongly temperature dependent shapes (FWHM) and peak wavelengths. This paper describes how a study of these features, both astronomically and in the laboratory, can lead to constraints on the temperatures of interstellar dust grains. This is demonstrated in part by comparing several astronomical spectra with laboratory spectra of H2O ice.

The star-formation process is an outstanding and largely unsolved problem in astrophysics. The role of magnetic fields is unclear but is widely considered to be important at all stages of protostellar evolution, from cloud collapse to ZAMS. For example, in some hydromagnetic models, the field may assist in removing angular momentum, thereby driving accretion and perhaps bipolar outflows.

Spectropolarimetry between 8 and 13μm provides information on the direction of the transverse component of a magnetic field through the alignment of dust grains. We present results of 8–13μm spectropolarimetric observations of a number of bipolar molecular outflow sources, and compare the field directions observed with the axes of the outflows and putative disk-like structures observed to be associated with some of the objects. There is a strong correlation, though so far with limited statistics, between the magnetic field and disk orientations. We compare our results with magnetic field configurations predicted by current models for hydromagnetically driven winds from the disks around Young Stellar Objects (YSOs). Our results appear to argue against the Pudritz and Norman model and instead seem to support the Uchida and Shibata model.

The Teff (effective temperature) scale for M dwarfs is very uncertain. One method which can be used to establish this scale is to compare observed spectra to synthetic ones derived from appropriate model atmospheres. With this method the adequacy of the model atmosphere is of great importance and simple models can give incorrect results. Alternatively if the Teff scale is known with some accuracy then this comparison is a good test of the adequacy of the models. We have computed some new and preliminary model atmospheres for late type dwarfs which accurately treat the line opacity with the opacity sampling technique and employ laboratory values for the transition strengths of molecular bands. With the above two considerations in mind we compare the fluxes of these models to observed fluxes of late K and early M dwarfs. This preliminary analysis indicates a discrepancy with the currently accepted Teff scale for early M dwarfs with the models suggesting values some 200 K hotter.

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.

The effects of the specific geometry of the magnetic field (such as field lines with torsion) on curvature emission and absorption in pulsar magnetospheres are discussed. Curvature maser emission can arise from two effects: the curvature drift, as has already been discussed in the literature, and field line torsion as discussed here in detail for the first time. Maser emission due to field line torsion can operate only when the Lorentz factor is larger than a certain value. However, when the Lorentz factor of electrons or positrons is sufficiently high, curvature masering is due to both curvature drift and magnetic field line torsion. The optical depth in the case of field line torsion is estimated. It is shown that if torsion is due to rotation, the resultant luminosity should be dependent on the rotation period in such a way that shorter periods correspond to larger luminosities.

We present spectropolarimetric observations of the type Ia supernova 1992A obtained 2 weeks and 7 weeks after maximum light. No significant polarisation was detected across any of the spectral features.

The Edinburgh-Cape Bright QSO Survey is a very small sub-set of the Edinburgh Cape Blue Object Survey, which is a major survey to discover blue stellar objects brighter than B~18 in the southern sky. It will cover an area of sky of 10,000 square degrees with |b|>30 and dec <0. The blue stellar objects are selected by automatic techniques from U and B pairs of UK Schmidt Telescope plates scanned with the COSMOS measuring machine. Follow-up photometry and spectroscopy is being obtained with the SAAO telescopes to classify the types of objects brighter than B=16.5, with some of the more stubborn objects being subjected to AAO service spectroscopy. Some preliminary results for the 6% QSO minority are presented in this paper and comparison is made with the Palomar-Green QSO Survey in the north, which we find to be at least a factor of two incomplete.