We have recently developed a detailed analytical model for powerful radio sources based on the results of a series of 2-D numerical hydrodynamical simulations. Here we make use of the model results to investigate the radio source luminosity evolution. Changes in the radio spectrum due to radiation losses were calculated in two different scenarios for energy gains/losses: Kardashev–h;Pacholczyk (KP) and ‘continuous injection’ (CI). The magnetic field was calculated in two limiting cases: (1) assuming equipartition of energy between relativistic particles and fields and (2) magnetic flux conservation inside the cocoon. The effect of the surrounding medium was taken into account by considering three different ambient density profiles. The evolutionary tracks were plotted in a power–diameter (P-D) diagram and compared with the predictions of self-similar models. In general, the evolutionary tracks cannot be represented by a simple power law and have a complex form that is most probably the result of the nonself-similar evolution of the source.

It is possible to detect gravitationally-lensed quasars spectroscopically if the spectra obtained during galaxy surveys are searched for the presence of quasar emission lines. The up-coming 6 degree Field (6dF) redshift survey on the United Kingdom Schmidt Telescope will involve obtaining ~105 spectra of near-infrared selected galaxies to a magnitude limit of K = 13. Applying previously developed techniques implies that at least one lens should be discovered in the 6dF survey, but that as many as ten could be found if quasars typically have BJ – K ~ 8. In this model there could be up to fifty lensed quasars in the sample, but most of them could only be detected by infrared spectroscopy.

In designing a stellar spectrograph, it is pointless to exceed the resolving power necessary to obtain all the information from the spectrum of a star. This is limited mainly by atomic thermal motions, giving rise to the Doppler broadening of spectral lines, by turbulence and rotation of the stellar atmospheres in which the lines are formed, and by collisional broadening.

The radio sky at lower frequencies, particularly below 20 MHz, is expected to be a combination of increasingly bright non-thermal emission and significant absorption from intervening thermal plasma. The sky maps at these frequencies cannot therefore be obtained by simple extrapolation of those at higher frequencies. However, due to severe constraints in ground-based observations, this spectral window still remains greatly unexplored. In this paper, we propose and study, through simulations, a novel minimal configuration for a space interferometer system which would enable imaging of the radio sky at frequencies well below 20 MHz with angular resolutions comparable to those achieved at higher radio frequencies in ground-based observations by using the aperture synthesis technique. The minimal configuration consists of three apertures aboard Low Earth Orbit (LEO) satellites orbiting the Earth in mutually orthogonal orbits. Orbital periods for the satellites are deliberately chosen to differ from each other so as to obtain maximum (u,v) coverage in short time spans with baselines greater than 15 000 km, thus, giving us angular resolutions finer than 10 arcsec even at these low frequencies. The sensitivity of the (u,v) coverage is assessed by varying the orbit and the initial phase of the satellites. We discuss the results obtained from these simulations and highlight the advantages of such a system.

The IUE observations of SN 1987A are presented and the most important results are briefly summarised. The photometric observations of SN 1987A are discussed in some detail in the context of the supernova energetics. Adding the information from spectroscopy and neutrino observations, it is concluded that SN 1987A is a ‘normal’ Type II explosion (i.e. core collapse of a massive star) with an unusually compact initial configuration, just as expected for the progenitor Sk −69°202.

Line absorption associated with the 12.2 GHz 20 − 3-1 transition of CH3OH has been mapped towards Sgr A with the Parkes 64-m radio telescope and a 2 arcmin beam. Two concentrations are present, both offset from the continuum peak, with velocities of 18 and 46 km s-1 and line-to-continuum ratios of 0.59 and 0.30. For the higher ratio the column density is almost 1017 cm-2. The concentrations may be associated with a molecular cloud which overlies Sgr A East but lies in part behind Sgr A West.

A search has been made using the Buckland Park air shower array for evidence of any excess of events from the direction of the recent supernova in the Large Magellanic Cloud. Upper limits resulting from this search and their significance are discussed in this paper.

I discuss the implications of the Parkes Multibeam Southern Sky HI Survey for cosmology. It will determine the local mass function of HI clouds, detecting several hundred per decade of mass. Each of these will come with a redshift and, for the more massive clouds, an estimate of the velocity width. This will provide an ideal database for peculiar motion studies and for measurements of biasing of galaxies relative to the underlying matter distribution.

A nearly stationary pulsar wind is shown to be always collimating along the direction of rotation. It follows that the conventional picture of the equatorial pulsar wind can occur only in a highly time-dependent manner, which, if true, may account for the observed time variation within a single pulse. Furthermore, a mechanism, via excitation of magnetosolitons, is proposed for explaining the continuous generation of energetic electrons, which yield the observed radio emission in the Type II supernova remnants. Fully relativistic analyses will be presented to substantiate these claims.

Models of hierarchical galaxy formation predict that large numbers of low-mass, dark matter halos remain around galaxies today. These models predict an order of magnitude more halos than observed stellar satellites in the Local Group. One possible solution to this discrepancy is that the high-velocity clouds (HVCs) around the Milky Way may be associated with the excess dark matter halos and be the gaseous remnants of the galaxy formation process. If this is the case, then analogues to the HVCs should be visible in other groups. In this paper, I review the observations of Hi clouds lacking stars around other galaxies and in groups, present early results from our Hi survey of loose groups analogous to the Local Group, and discuss implications for the nature of HVCs and galaxy formation.

The nature and cause of the double-mode (DM) pulsation in beat Cepheid variable stars is still a matter of considerable uncertainty. Recently, evidence has been accumulating that the relative energy of the two modes in any particular star may be a slowly varying function of time. For TU Cas, Hodson, Stellingwerf and Cox (1979) have found that the first overtone amplitude has been decreasing over a 67 year timebase, while the present authors (Faulkner and Shobbrook 1979) have reported an increase in overtone energy in U TrA over 20 years. Observational details of the form of the mode energy changes may be helpful in obtaining a better understanding of these stars (see Shobbrook and Faulkner 1982). Our present observations of U TrA have been obtained to investigate its energy changes more fully.

One of the major science goals of the SkyMapper survey of the Southern Hemisphere sky is the determination of the shape and extent of the halo of the Galaxy. In this paper, we quantify the likely efficiency and completeness of the survey as regards the detection of RR Lyrae variable stars, which are excellent tracers of the halo stellar population. We have accomplished this via observations of the RR Lyrae-rich globular cluster NGC 3201. We find that for single-epoch uvgri observations followed by two further epochs of g, r imaging, as per the intended three-epoch survey strategy, we recover known RR Lyraes with a completeness exceeding 90%. We also investigate boundaries in the gravity-sensitive single-epoch two-colour diagram that yield high completeness and high efficiency (i.e., minimal contamination by non-RR Lyraes) and the general usefulness of this diagram in separating populations.

We have used the TAURUS Fabry–Perot mapping spectrometer on the William Herschel telescope (WHT) to produce a complete kinematic map of the disk of M100 in Hα. Here we show how the internal velocity dispersion (σ) of the principal emission components of the brightest regions varies with their Hα luminosity. The plot shows ample scatter, but an upper envelope in σ is clearly linear (in the log–log plane) with a slope of 2·6, a result which agrees precisely with an earlier graph by Arsenault et al., who selected instead the regions of highest surface brightness. We show that this result, which differs from the conventional prediction from the virial theorem, is consistent with virialisation if the H II regions are density bounded, and thus offers evidence in support of the density bounding hypothesis for the most luminous regions in disk galaxies.

Astro Concepts is a project within Swinburne University of Technology in Melbourne developing browser-based software modules on Optical Telescopes, Nebulae and Binary Stars. The modules are designed to enhance students' understanding of basic physics concepts, which underlie introductory-level conceptual astronomy courses. When complete, the Astro Concepts modules will be available for use in university courses in introductory astronomy, introductory physics teaching, secondary teaching and online astronomy education. The strategy outlined here is to obtain a reasonable level of understanding of the necessary physics concepts by presenting them embedded in relevant and interesting astronomy contexts, and by the use of an engaging educational approach requiring active learning by the student.

We have constructed theoretical spherical dust shell models using a full radiative transfer treatment, to investigate the effect of thermal emission on the strengths of molecular CO and H2O features in late type stars with circumstellar dust shells and to establish the optical depth at which the strengths of the bands are significantly affected. In this study, for the first time the central sources have been represented by realistic atmospheric models for cool stars in the temperature range 2500–3000 K, which are representative of the central stars of OH/IR sources. Parameters of the dust shell models were chosen to fit the observed run of colours from 1.25–5 μm of a large sample of OH/IR sources using ‘dirty silicate opacities’. The results show that the molecular band strengths in the 2 μm region are significantly affected by the dust emission only when the optical depth in the shell reaches a value of τ1μm ≈2 for T* = 2500 K and somewhat less for T* = 3000 K. However, the changes are such that the distinction between supergiant-like spectra, and variable M-star spectra is retained in models with very high shell optical depths. The implications of these models are discussed in relation to previous observations of OH/IR sources.

It is widely believed that stars form from collapsing interstellar clouds. However, molecular clouds typically contain of the order of 103 solar masses. Thus a mechanism is required that allows a collapsing cloud to fragment into a number of collapsing stellar sized sub-condensations. The early work was based on a virial theorem approach—defining a critical mass a cloud must exceed in order for its gravitational force to overcome the resistive thermal, rotational and magnetic forces, thus allowing the cloud to collapse. This critical mass is analogous to the Jeans mass for non-rotating, non-magnetic clouds. It is thought that a cloud containing several critical masses may collapse into several sub-condensations. Further, it is thought that the galactic magnetic field will cause the critical mass to decrease as the cloud collapses, allowing the cloud to fragment into a number of sub-condensations. The critical mass decreases as the cloud flattens down the field lines (since Mcrit ∝ B3/ϱ2 and B ∝ ϱk, K < ⅔ for non-isotropic collapse).