The use of role-playing exercises in the teaching of university astronomy and physics can enliven lectures, deepen student understanding and dramatically increase the level of classroom interaction. A series of case studies is presented, illustrating the nature of this technique, its advantages and some of its pitfalls. Several ready-to-run exercises are included.

Given the growing use of Sérsic's (1963, 1968) R 1/n model for describing the stellar distributions in galaxies, and the lack of any single reference that provides the various associated mathematical expressions, we have endeavoured to compile such a resource here. We present the standard intensity profile, and its various guises such as the luminosity, surface-brightness, and aperture–magnitude profile. Expressions to transform the effective surface brightness into the mean effective and central surface brightness are also given, as is the expression to transform between effective radii and exponential scale-lengths. We additionally provide expressions for deriving the ‘concentration’ of an R 1/n profile, and two useful equations for the logarithmic slope of the light-profile are given. Petrosian radii and fluxes are also derived for a range of Sérsic profiles and compared with the effective radii and total flux. Similarly, expressions to obtain Kron radii and fluxes are presented as a function of the Sérsic index n and the number of effective radii sampled. Illustrative figures are provided throughout. Finally, the core–Sérsic model, consisting of an inner power-law and an outer Sérsic function, is presented.

We present a summary of a recent meeting held in honour of Brent Tully's 60th birthday. We also provide a retrospective on his career to date.

This article describes a method to turn astronomical imaging into a random number generator by using the positions of incident cosmic rays and hot pixels to generate bit streams. We subject the resultant bit streams to a battery of standard benchmark statistical tests for randomness and show that these bit streams are statistically the same as a perfect random bit stream. Strategies for improving and building upon this method are outlined.

Samples of CSS/GPS sources suitable for statistical studies have been selected from the 3CR catalogue and from the Peacock & Wall catalogue. The selection criterion used for the Peacock & Wall catalogue CSS/GPS sources selects sources which peak below about 2 GHz and are therefore larger than ˜200 pc. Our main aim is to find among the flat spectrum sources in the Peacock & Wall catalogue smaller size CSS/GPS sources by means of systematic high resolution observations. The discovery of a few more would be important in order to finally have a complete flux limited sample of this class of objects. We discuss the results obtained so far for three of the observed sources.

X-ray binaries in which the accreting component is a neutron star commonly exhibit significant changes in their spin. In the system Cen X-3, a disk accreting binary system, the pulsar was observed to spin up at a rate ḟ = 8 × 10−13 Hz s−1 when averaged over the past twenty years, but significant fluctuations were observed above this mean. Recent BASTE observations have disclosed that these fluctuations are much larger than previously noted, and appeared to be a system characteristic. The change in the spin state from spin-up to spin-down or vice-versa occurs on a time scale that is much shorter than the instrument can resolve (≤1 d), but appears always to be a similar amplitude, and to occur stochastically. These observations have posed a problem for the conventional torque–mass accretion relation for accreting pulsars, because in this model the spin rate is closely related to the accretion rate, and the latter needs to be finely tuned and to change abruptly to explain the observations. Here we review recent work in this direction and present a coherent picture that explains these observations. We also draw attention to some outstanding problems for future studies.

Propagation effects on radio emission within the pulsar magnetosphere are discussed. Widely accepted pulsar models assume that a pulsar magnetosphere is populated with relativistic pair plasmas produced through electron–positron cascades by accelerated primary particles above the polar cap. Any radio emission produced well inside the light cylinder (the radius at which the rotation speed equals c) must propagate through the magnetospheric plasma and be subject to plasma dispersion effects such as refraction and absorption. The observed pulse profiles should contain some features that reflect the influence of the intervening plasma. I discuss particularly the absorption effect due to cyclotron resonance and its possible observational consequences.

In their study of the evolution of galaxies within clusters, Butcher and Oemler discovered evidence for a strong evolution in star-formation rate with redshift. Later studies confirmed this conclusion and uncovered several aspects of the effect: photometric, spectroscopic, and morphological. This article reviews a broad sample of these works and discusses selection effects, biases, and driving mechanisms that might be responsible for the changes in star-formation rate.

Powerful extragalactic radio sources are characterised by kpc-scale synchrotron emission associated with highly-collimated outflows of relativistic plasma. It is hypothesised that this outflowing plasma is powered by accretion processes concomitant with a central massive black hole. The radio morphologies of these sources comprise jets, lobes and for the most powerful sources, hotspots. At first sight, powerful extragalactic radio sources are a mixed group of objects, with the result that only some gross property delineates them further (e.g. steep-spectrum or flat-spectrum). However, there is accumulating observational evidence which suggests that it is the orientation of the radio axis to our line of sight that dictates their observed characteristics. This orientation dependence has been incorporated into ‘unified schemes’, which physically link apparently disparate radio source types via the random orientation of a ‘parent’ population on the plane of the sky. This paper summarises the ‘dual-population unified scheme’ paradigm investigated by Wall & Jackson (1997) and Jackson & Wall (1999) and discusses some of its implications with respect to radio source cosmology.

We present a detailed inhomogeneous chemical evolution study that considers for the first-time neutron star mergers as major r-process sources, and compare this scenario with the ones in which lower-mass (in the range 8–10 M⊙) or higher-mass core-collapse supernovae (with masses ≥20 M⊙) act as dominant r-process sites. We conclude that it is not possible at present to distinguish between the lower-mass and higher-mass supernovae scenarios within the framework of inhomogeneous chemical evolution. However, neutron-star mergers seem to be ruled out as the dominant r-process source, since their low rates of occurrence would lead to r-process enrichment that is not consistent with observations.

The existence of a stream of tidally stripped stars from the Sagittarius dwarf galaxy demonstrates that the Milky Way is still in the process of accreting mass. More recently, an extensive stream of stars has been uncovered in the halo of the Andromeda galaxy (M31), revealing that it too is cannibalising a small companion. This paper reports the recent observations of this stream, determining its spatial and kinematic properties, and tracing its three-dimensional structure, as well as describing future observations and what we may learn about the Andromeda galaxy from this giant tidal stream.

Australasian amateur astronomers, Grigg and Ross, discovered four different comets between 1902 and 1907. Controversy surrounding these discoveries led to a deterioration in relations between Australia's leading amateur astronomers and Baracchi at Melbourne Observatory, and to the eventual transfer of the ‘Australian Central Bureau’ to Sydney Observatory.

With the ATNF Mopra telescope we are performing a survey in the 12CO(1–0) line to map the molecular gas in the Large Magellanic Cloud. For some regions we also obtained interferometric maps of the high density gas tracers HCO+ and HCN with the Australia Telescope Compact Array. Here we discuss the properties of the elongated molecular complex that stretches about 2 kpc southward from 30 Doradus. Our data suggest that the complex, which we refer to as the ‘molecular ridge’, is not a coherent feature but consists of many smaller clumps that share the same formation history. Likely triggers of molecular-cloud formation are shocks and shearing forces that are present in the surrounding south-eastern Hi overdensity region, a region influenced by strong ram pressure and tidal forces. The molecular ridge is at the western edge of the the overdensity region where a bifurcated velocity structure transitions into a single disk velocity component. We find that the 12CO(1–0) and Hi emission peaks in the molecular ridge are typically near each other but never coincide. A likely explanation is the conversion of warmer, low-opacity Hi to colder, high-opacity Hi from which H2 subsequently forms. On smaller scales we find that very dense molecular gas, as traced by interferometric HCO+ and HCN maps, is associated with star formation along shocked filaments and with rims of expanding shell-like structures, both created by feedback from massive stars.

An examination is made of the relationship between the observed energy spectrum of cosmic rays and the averaged spectrum of the cosmic rays at their sources. These spectra differ greatly, due to propagation effects. A form of the source spectrum is deduced which is a rather featureless power law over the full range of observations from 1010 eV to 1020 eV. We suggest that this lack of features is indicative of a common source for all cosmic rays over the full energy range, as opposed to lower energy Galactic and higher energy intergalactic components such as is often suggested.

We have carried out a study of the neutral hydrogen in the direction of the X-ray source 1E 161348–5055, a compact central object (CCO) located in the interior of the supernova remnant (SNR) RCW 103. The Hi 21 cm line observations were carried out using the Australia Telescope Compact Array, complemented with single dish data from the Parkes radio telescope to recover information at all spatial scales. We derive a distance to RCW 103 of 3.1 kpc, in agreement with previous distance measurements. We have also detected a small hole in the Hi emission which is positionally and kinematically coincident with the location of the CCO which confirms the association between the SNR and the CCO. This is the third case of a depression in Hi emission seemingly associated with CCOs in SNRs. The characteristic parameters of the holes such as their size, eccentricity and evacuated mass are similar in all three cases. We estimate the absorbing HI column density towards 1E 161348–5055 to be ∼6 × 1021 cm–2, a value compatible with a blackbody solution for the CCO X-ray emission. However, the implied temperature and luminosity are very high compared to most neutron stars. Moreover, the strong long-term variability in X-rays favours the hypothesis that 1E 161348–5055 is an accreting binary source rather than an isolated, cooling neutron star. An analysis of the continuum image obtained at 1.4 GHz from these observations shows no trace of a pulsar wind nebula around 1E 161348–5055, in spite of it being a young object.

Knowledge about the age of presolar grains provides important insights into Galactic chemical evolution and the dynamics of grain formation and destruction processes in the Galaxy. Determination from the abundance of cosmic ray interaction products is straightforward, but in the past has suffered from uncertainties in correcting for recoil losses of spallation products. The problem is less serious in a class of large (tens of μm) grains. We describe the correction procedure and summarise results for He and Ne ages of presolar SiC ‘Jumbo’ grains that range from close to zero to ∼850 Myr, with the majority being less than 200 Myr. We also discuss the possibility of extending our approach to the majority of smaller SiC grains and explore possible contributions from trapping of cosmic rays.

We describe a newly refined procedure for making optical identifications of radio sources in Abell cluster fields observed with the Molonglo Observatory Synthesis Telescope (MOST). The method is based on past experience but uses a range of new tools to improve the reliability and production rate of identification lists. The COSMOS/UKST Southern Sky Object Catalogue was used to make preliminary identifications which were then inspected visually with the assistance of computer generated overlays of the MOST images and the Digitized Sky Survey (DSS). The overlaid images were essential for securing identifications for the extended sources prevalent among nearby clusters.

We find 21±1·5% of the radio sources are identified with galaxies and 4·6±0·7% with QSO candidates in a sample of 927 radio sources in 27 cluster fields. We make a preliminary attempt to separate cluster radio galaxies from interlopers on the basis of absolute magnitudes. A strong concentration of radio galaxies was found at projected distances less than 100 kpc from the cluster centres and a weaker concentration for projected distances of 100–500 kpc.

Variable absorption features were observed in the visible and ultraviolet spectrum of β Pictoris soon after this star gained attention in the early 1980s due to its large IRAS infrared excess and the discovery, from optical imaging, of an edge-on dust disk. The absorption has been attributed to the evaporation of infalling planetesimals or comet-like bodies (the falling evaporating bodies, or FEB, hypothesis). With a view to confronting this hypothesis with fuller observations, we monitored the Ca II H and K lines in β Pictoris simultaneously during 1998, obtaining sequences of spectra on 50 nights. Variable absorption was usually present. The different oscillator strengths of the H and K lines permit the determination of covering factors, but detailed modelling is required to test whether all features can be explained by the FEB hypothesis. The blend of Ca II H with Balmer H ε means that the H and K photospheric profiles are different, and that the variable absorption features do not evolve in parallel. The behaviour of the variable absorption on November 27 is evocative of a body passing in front of the stellar disk in a prograde equatorial orbit.