This paper summarises our work on the role of magnetic fields in accretion disks presented in two papers elsewhere. In the first part (a summary of part of Kuncic & Bicknell 1999), we present a formal development of the equations governing the structure of an accretion disk containing magnetohydrodynamic turbulence. The importance of the different terms in the energy and momentum equations is discussed, and a parametrisation of the unresolved processes is suggested that could be used to make further progress. We briefly explore whether an MHD accretion disk can transport a significant part of the gravitational power into a corona by buoyancy. In the second part, we present some exploratory calculations of the vertical structure of accretion disks, in which non-local dissipation of energy due to the buoyant transport of magnetic field energy is taken into account. It is argued that the efficiency of buoyant magnetic transport depends very strongly on the size of the coherent magnetic regions. If the size of the buoyant cells is not very close to the disk thickness, magnetic energy generated by dynamo action inside the disk will be dissipated locally, and will not be available to transport a significant part of the accretion luminosity into a corona.

In this paper, we give a brief summary of the talks on accretion processes in AM Herculis systems which were presented at the ANU Astrophysical Theory Centre workshop on ‘Magnetic Fields and Accretion’. One of the topics to be discussed was the mechanism that leads to the formation of magnetically funnelled accretion flows in close interacting magnetic binaries. New solutions to the Bernoulli integral indicate that the field lines must be twisted and have a strong toroidal component at the base of the funnel in order for channelled flow to be possible. The magnetic field pressure of these toroidal fields first lifts the material out of the orbital plane allowing it to ‘levitate’ before freely falling along magnetic field lines towards the stellar surface. Results of recent calculations of the thermal structure and radiation properties of accretion funnels were also presented. These new 3D calculations allow for heating by the soft X-rays originating from the accretion shock, and by magnetic heating at the base of the funnel, and determine self-consistently the thermal structure, and the continuum and line emissions, allowing for both transfer of the external radiation field and the trapping of radiation within the funnel. Calculations were also presented of the expected properties of H- and He-like Fe lines originating from the accretion shock itself at the stellar surface. These lines are predicted to be rather strong and can be used as diagnostics of the accretion flow. Finally, the stability of the accretion shock was also addressed. In particular, it was shown that radiative cooling may cause thermal instability and an oscillatory behaviour, with two competing processes coming into play: bremsstrahlung cooling, which promotes instability, and cyclotron cooling, which tends to dampen the oscillations.

Optical and X-ray spectroscopy indicate that the X-ray pulsar GX 1+4 is seen through a cloud of gravitationally bound matter. We discuss an unstable negative feedback mechanism (originally proposed by Kotani et al. 1999), based on X-ray heating of this matter which controls the accretion rate when the source is in a low X-ray luminosity state. A deep minimum lasting ∼6 hours occurred during observations with the RXTE satellite over 1996 July 19–21. The shape of the X-ray pulses changed remarkably from before to after the minimum. These changes may be related to the transition from neutron star spin-down to spin-up which occurred at about the same time. Smoothed particle hydrodynamic simulations of the effect of adding matter with opposite angular momentum to an existing disk, show that it is possible for a number of concentric rings with alternating senses of rotation to co-exist in a disk. This could provide an explanation for the step-like changes in Ṗ which are observed in GX 1+4. Changes at the inner boundary of the disk occur at the same timescale as that imposed at the outer boundary. Reversals of material torque on the neutron star occur at a minimum in LX.

We present the first results from a study of the radio continuum properties of galaxies in the 2dF Galaxy Redshift Survey, (2dFGRS) based on thirty 2dF fields covering a total area of about 100 deg2. About 1·5% of galaxies with bJ < 19·4 mag. are detected as radio continuum sources in the NRAO VLA Sky Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are active galaxies (mostly low-power radio galaxies and a few Seyferts). The combination of 2dFGRS and NVSS will eventually yield a homogeneous set of around 4000 radio-galaxy spectra, which will be a powerful tool for studying the distribution and evolution of both AGN and starburst galaxies out to z ∼ 0·3.

A radio continuum survey of X-ray-identified weak-lined T Tauri stars (WTTs) in the newly-discovered η Chamaeleontis cluster has been completed using the Australia Telescope Compact Array (ATCA). The 10 known WTTs in the cluster form a unique sample of codistant late-type pre-main-sequence stars with ages of ~8 Myr and masses ranging from 0·1–1·0 M⊙. Our survey detected none of the 10 X-ray-emitting WTTs with 3σ sensitivity limits at 4·8 and 8·6 GHz (6·2 and 3·5 cm) of typically 0·4 mJy, corresponding to a radio luminosity of 4·5 ×1015 erg Hz−1 s−1. Rotation periods for these stars indicate that they are not, as a group, fast-rotating stars. The non-detection in the radio bands supports the findings of other radio surveys of inhomogeneous samples of young stars, where radio emission is fairly common (10–30%) among very young T Tauri stars across all late spectral types, but confined to rapidly-rotating F-G-K stars amongst older zero-age main sequence stars. Rotation, more than youth, appears to be the key to radio emission in young stars.

Modelling of extreme scattering events suggests that the Galaxy's dark matter is an undetected population of cold, AU-sized, planetary-mass gas clouds. None of the direct observational constraints on this picture—thermal/non-thermal emission, extinction and lensing—are problematic. The theoretical situation is less comfortable, but still satisfactory. Galactic clouds can survive in their current condition for billions of years, but we do not have a firm description for either their origin or their evolution to the present epoch. We hypothesise that the proto-clouds formed during the quark–hadron phase transition, thereby introducing the inhomogeneity necessary for compatibility with light element nucleosynthesis in a purely baryonic universe. We outline the prospects for directly detecting the inferred cloud population. The most promising signatures are cosmic-ray-induced Hα emission from clouds in the solar neighbourhood, optical and X-ray flashes arising from cloud–cloud collisions, ultraviolet extinction, and three varieties of lensing phenomena.

In late 1998 the International Gemini Project Office identified a need for a low cost, near-infrared spectrograph to be commissioned on the Gemini South telescope on the shortest possible timescale. In response, the Research School of Astronomy and Astrophysics of the Australian National University proposed to design, construct, and commission a near-infrared, integral-field spectrograph on Gemini. The science drivers and novel design of the Near-infrared Integral-Field Spectrograph (NIFS) are described in this paper. NIFS will achieve significant economies in cost and schedule in several ways:

• By addressing targeted science with high efficiency. NIFS will primarily target velocity measurements in galaxies to study the demographics of black holes in galactic nuclei and the evolution of structural properties in high redshift galaxies. However, NIFS will also be applied to a wide range of general astronomical topics, but these will not dictate the instrument design.

• By adopting a largely fixed-format design. A 3·2″ × 3·2″ ‘stair-case’ integral field unit (IFU) will feed a near-infrared spectrograph with four fixed-angle gratings mounted on a single grating wheel. A single, fixed-format camera will form the spectral image on a 2048 × 2048 Rockwell HgCdTe HAWAII-2 array. Two-pixel spectral resolving powers of ∼5400 will be achieved with complete wavelength coverage in each of the J, H, and K photometric bands through 32 optimally sampled 0·1″ wide slitlets. The velocity resolution of ∼55 km s−1 will be sufficient to achieve the targeted science objectives, and will allow software rejection of OH airglow lines.

• By packaging the NIFS instrument within a duplicate of the Near-Infrared Imager (NIRI) cryostat. The NIRI cryostat, On-Instrument Wavefront Sensor (OIWFS), detector focusing mechanism, control system, and EPICS software will all be duplicated with only minimal change. Construction of the duplicate NIRI cryostat, OIWFS, and control system will be done by the University of Hawaii.

Kodak Technical Pan (Tech Pan) emulsion on a film base has been in use at the UK Schmidt Telescope (UKST) since 1992. This material is extremely fine grained and its resolution is well matched to images produced by the UKST under good conditions. Tech Pan yields wide-angle photographs that are about 1 (stellar) magnitude fainter than equivalent IIIa-F plates but have considerably lower grain noise. A wide variety of new projects are under way which take advantage of this remarkable material. In this paper empirical results from experiments with Tech Pan from a number of sources are tied in with UKST experience to present an overview of the properties of the emulsion from an astronomical perspective. We compare Tech Pan's properties with those of equivalent IIIa-F emulsion, to which it seems superior in almost every respect. This overview and groundwork are currently missing from the published astronomical literature. The technical background and developments leading to adoption of this material at the UKST are presented.