Some unsolved cosmological questions remain in relation to the formation of structure in the universe. One way of addressing such questions is to use rich galaxy clusters as tracers of the growth of large-scale structure. To date, studies of rich clusters of galaxies have concentrated on systems generally at either high redshift or in the local universe. The properties of clusters and their constituent galaxies at these extrema are becoming well understood. In particular, it is becoming clear that rich clusters have undergone considerable evolution both dynamically and in their galaxy populations over the last 5–8 Gyr. We are undertaking a detailed study of rich clusters of galaxies in the range 0·05 ≲ z ≲ 0·15. Our results will be directly comparable to those of previous studies both at high and low redshift and, for the first time, provide continuous coverage across this important and unexplored transitory epoch in terms of galaxy evolution and structure growth.

We have used two subsamples of superluminal quasars to test the relativistic beaming model, and to place useful constraints on the radio source orientation hypothesis and cosmology. Based on the variation of the observed ratio R of the core-to-lobe radio luminosities with proper motion μ for the subsample of lobe-selected quasars, we show that the observed R–μ data can be explained in terms of a bulk relativistic motion with Lorentz factor γ≈4. Also, from the observed proper motion versus redshift (μ–z) plot for this subsample, we show that γ≈4 implies a high density universe with deceleration parameter q0 = 0·5. Furthermore, from the observed (μ–z) plot for the two subsamples taken separately, we show that both γ and μ for the core-selected subsample exceed those of the lobe-selected subsample by a factor of 2 for the q0 = 0·5 world model. This result is demonstrated to be consistent with an orientation-based unified scheme in which lobe-selected quasars lie, on the average, at an angle which is a factor of ∼2–3 larger than that of their core-selected counterparts.

A recent study by Wylie et al. (2006) has revealed that s-process element abundances are enhanced relative to iron in both red giant branch and asymptotic giant branch stars of 47 Tuc. A more detailed investigation into s-process element abundances throughout the colour-magnitude diagram of 47 Tuc is vital in order to determine whether the observed enhancements are intrinsic to the cluster. This paper explores this possibility through observational and theoretical means. The visibility of s- and r-process element lines in synthetic spectra of giant and dwarf stars throughout the colour magnitude diagram of 47 Tuc has been explored. It was determined that a resolving power of 10 000 was sufficient to observe s-process element abundance variations in globular cluster giant-branch stars. These synthetic results were compared with the spectra of eleven 47 Tuc giant branch stars observed during the performance verification of the Robert Stobie Spectrograph on the Southern African Large Telescope. Three s-process elements (Zr, Ba and Nd) and one r-process element (Eu) were investigated. No abundance variations were found such that [X/Fe] = 0.0 ± 0.5 dex. It was concluded that this resolving power, R ∼ 5000, was not sufficient to obtain exact abundances but upper limits on the s-process element abundances could be determined.

Microlens-induced variability in multiple quasars can be used to study two cosmological issues of great interest, the size and brightness profile of quasars on one hand, and the distribution of compact (dark) matter along the line of sight on the other. Here a summary is given of recent theoretical progress as well as observational evidence for quasar microlensing, plus a discussion of desired observations and required theoretical studies.

The RGU-photographic investigation of an intermediate latitude field in the direction to the Galactic centre is presented. 164 extra-galactic objects, identified by comparison of Minnesota and Basel charts, are excluded from the program. Also, a region with size 0.104 square-degrees, contaminated by cluster (M5) stars and affected by background light of the bright star HD 136202 is omitted. Contrary to previous investigations, a reddening of E(B – V) = 0.046, corresponding to E(G – R) = 0.07 mag is adopted. The separation of dwarfs and evolved stars is carried out by an empirical method, already applied in some of our works. A new calibration for the metallicity determination is used for dwarfs, while the absolute magnitude determination for stars of all categories is performed using the procedures given in the literature. There is good agreement between the observed logarithmic space density histograms and the galactic model gradients. Also, the local luminosity function agrees with Gliese's (1969) and Hipparcos (Jahreiss & Wielen 1997) luminosity functions, for stars with 2 < M(G) ≤ 8 mag. For giants, we obtained two different local space densities from comparison with two Galactic models, i.e. D*(0) = 6.63, close to that of Gliese (1969), and D*(0) = 6.79. A metallicity gradient, d[Fe/H]/dz = –0.20 dex kpc–1, is detected for dwarfs (only) with absolute magnitudes 4 < M(G) ≤ 6, corresponding to a spectral type interval F5–K0.

We construct binary-star population nucleosynthesis models of carbon-enhanced metal-poor (CEMP) stars. We compare the CEMP to extremely metal-poor (EMP) ratio of our models to the observed ratio and find it is an order of magnitude too small. Through an increase in the efficiency of third dredge-up in low-mass, low-metallicity, thermally-pulsing Asymptotic Giant Branch (TP-AGB) stars our models better match the observations.

The main topic of this contribution is the investigation of the morphological self-similarity of the growth process during the gigahertz peaked spectrum (GPS) and compact steep spectrum (CSS) phase of evolving radio galaxies. By investigating a new sample of faint CSS radio sources we establish that self-similar evolution must hold for peaked spectrum sources over a wide range of luminosities as well as physical sizes. Thus, we argue that self-similarity should be regarded as an essential, intrinsic characteristic of the growth process of young radio sources, and be treated as such, and not merely as a supplementary constraint for evolution models.

The Australia Telescope and Anglo-Australian Telescope were used in May 2000 to record the radio and optical emissions from the dMe flare star Proxima Centauri. Eight bright optical flares over a two-day interval resulted in no detectable excess short-term radio emission at 1.38 and 2.50 GHz. However, a slowly declining 1.38 GHz emission over the two-day interval was nearly 100% right circular polarised and was restricted to a relatively narrow bandwidth with total intensity (I) and circular polarisation (V) varying significantly over the 104 MHz receiver bandwidth. These are the first observations to show that highly-polarised narrowband flare star emission can persist for several days. This signature is attributed to sources of coherent radio emission in the star's corona. Similarities with various solar radio emissions are discussed; however, it is not possible with the existing observations to distinguish between fundamental plasma emission and electron–cyclotron maser emission as the responsible mechanism.

UBV observations of the massive binary system TT Aur were carried out mainly at theTurkish National Observatory (TUG). These observations, together with IUE spectra and times of eclipse minima collected from the literature, were used to study the system parameters.

Simultaneous solution of the light curves by the Wilson-Devinney code allows a semi-detached configuration with a slightly larger Roche-lobe filling secondary. This picture is supported by other evidence. The shoulders of the primary minimum suggest some excess absorption, in keeping with circumstellar material in the form of a disk-like structure around the primary component. The deeper primary minimum in the U filter may indicate a hotter region on the secondary-facing hemisphere of the primary.

The period variation of the system can also be related to the possible existence of a third component in a circular orbit around the system.

An alternative detached representation is also considered using optimal curve-fitting techniques. We appeal for further observations to help resolve some outstanding issues in this interesting massive binary.

The inverse Compton (IC) limit, TB 1012 K, on synchrotron sources places a severe limit on models for intraday variables. The conventional limit is relaxed for proton synchrotron emission, or when acceleration balances IC losses. Coherent emission avoids the limit entirely but introduces other difficulties that have been inadequately discussed.

This paper deals with the spectral ageing study of a representative sample of compact symmetric objects (CSOs) and compact steep spectrum (CSS) sources. Observations reveal a distinctive high-frequency steepening of the radio spectra of many of these sources. The existence of such a spectral feature is expected or may be naturally interpreted in terms of radiative ageing of synchrotron emitting electrons. The small angular size of CSS sources makes it relatively easy to measure their integrated spectra over a wide frequency range for a conspicuous number of objects. For those sources whose emission is dominated by the mini-lobes, the integrated spectra can be used to constrain the source age. Assuming equipartition magnetic fields, the spectral ages we found are in the range from 102 to 105 yr. Multifrequency VLBA observations allow us to study the spectral properties of two CSOs: B1323+321 and B1943+546. The case of B1943+546 is particularly interesting since for this source a kinematic age has been derived from the proper motion of the hot spots. We found that spectral and kinematic ages agree within a factor of 2. The overall results presented here confirm that the CSOs and CSS sources are indeed young objects. Finally, we show some examples of compact sources characterised by an extraordinary steep and curved spectrum. It is plausible that these are relic sources in which the injection of fresh electrons has ceased for a significant fraction of their lifetime. These observations may indicate either the presence of intermittent activity or a class of short-living objects.

Throughout this paper we adopt H 0 = 100 h km s−1 Mpc−1 and q 0 = 0.5.

Microlensing observations may give us the first nano-arcsecond scale information about the structure of quasars. I review what is currently known about quasars on these scales, highlighting the principal uncertainties. I cover both the continuum emission and the broad line region. I conclude that little is firmly known about the structure of quasars.

In 1992 an NRAO 225-GHz site survey heterodyne radiometer was placed at the Geographical South Pole. The instrument operated over an entire annual cycle and provided direct measurements of the millimetre-wave sky brightness temperature as a function of zenith angle. Interpreted in a single-slab ‘skydip’ radiation transfer model of the atmosphere, these sky brightness measurements provided a time series of the millimetre atmospheric opacity. Statistics derived from this opacity time series were important for making comparisons with other candidate millimetre and sub-millimetre wave astronomy sites. This paper reexamines the 1992 measurements and the original analysis. Details of the skydip fit model, radiometer gain error, instrument stability, and a mid-season replacement to a window in the instrument enclosure combined to cause a modest under-reporting of the atmospheric opacity in previous reports. Unchanged are earlier conclusions that dry air makes a significant contribution to the total opacity at 225 GHz.

In addition to large numbers of normal galaxies, the multibeam HI Parkes all-sky survey will probably discover intergalactic HI clouds, very low-surface-brightness, gas-rich galaxies, and small HI clouds in nearby groups of galaxies. I will briefly discuss some aspects of why these classes of objects are interesting in the context of dark matter and galaxy formation.

Observational and theoretical evidence points to the existence of an unusually high magnetic field on GX 1+4. The pulsar is thus an ideal laboratory for studying two-photon cyclotron emission, an important source of photons of frequency significantly less than the cyclotron frequency in X-ray pulsars. Low-frequency approximations to the two-photon cyclotron emission transition probabilities are derived. These are used to calculate the theoretical opening angle of the double-humped pulse shape predicted by the two-photon cyclotron emission model. The theoretical pulse shape, incorporating the effects of gravitational light bending, is compared with observations of GX 1+4. Observed light curves have opening angles consistent with the theoretically predicted maximum value.

We present the results of a photometric survey for variability in ten X-ray-emitting low-mass stars in the Chamaeleon region. Eight of the stars we observed are bona fide pre-main-sequence members of the ∼2 Myr-old Chamaeleon I star-forming cloud. The other two stars are young with high levels of relative X-ray emission, but with discordant proper motions they are probable non-members of the cloud. In six of the stars we monitored, periodic variations on timescales of 2.5–11.5 d were detected, that we ascribe to stellar rotation and the presence of cool starspots. Two other stars, CHXR 20 and CHXR 85, show large amplitude variations at visual and near-infrared wavelengths and are candidate eclipsing binaries. Compared to the rotational properties of low-mass stars in the ≈8 Myr-old η Chamaeleontis cluster, we find that the older η Chamaeleontis stars have several times higher surface specific angular momentum than the younger Chamaeleon I stars. The apparent increase in angular momentum between ∼2 and 8 Myr might be due to changes in stellar internal structure as the stars evolve, or evidence for a different rotational history between members of the two star-forming regions.

Large-scale surveys provide new constraints on the structure and evolution of the Milky Way. The population synthesis approach is a useful tool to interpret such data sets and to test scenarios of evolution of the Galaxy. New constraints on Galactic parameters have been obtained from the Besançon model of population synthesis, in particular in the inner regions, thanks to near-infrared surveys less affected by interstellar extinction than the optical ones. We present here a few preliminary comparisons between observed and simulated distributions of proper motions in the direction of the Galactic bulge. Next we discuss how bulge stars can be observed and separated from other populations with the RAVE and Gaia surveys.

We test the hypothesis that high-velocity gas cloud Complex C is actually a high-latitude spiral arm extension in the direction of the Galactic warp, as opposed to the standard interpretation — that of a once extragalactic, but now infalling, gas cloud. A parallel Tree N-body code was employed to simulate the tidal interaction of a satellite perturber with the Milky Way. We find that a model incorporating a perturber of the mass of the Large Magellanic Cloud on a south to north polar orbit, crossing the disk at ˜15 kpc, does yield a high-velocity, high-latitude extension consistent with the spatial, kinematical, and column density properties of Complex C. Unless this massive satellite remains undiscovered because of either a fortuitous alignment with the Galactic bulge (feasible within the framework of the model), or the lack of any associated baryonic component, we conclude that this alternative interpretation appears unlikely.

MRC B1221–423 is a compact steep spectrum (CSS) radio source in the core of a remarkable elliptical galaxy. We examine its environment with long-slit spectra and multicolour images. A high-resolution synthesis image shows the radio source to have a 1″.5 (5.7 kpc) double structure. We use the empirical relationship between jet kinetic power and narrow line luminosity to infer a source age of ˜105 yr. The z = 0.1706 host galaxy is clearly disturbed, with tidal features and shells providing plausible evidence for a merger with one or more close companions. This evidence leads us to conclude that B1221–423 may be the progenitor of a much larger source, caught at an early stage in its radio evolution. We speculate that it is the interaction and accompanying events which have triggered this young powerful radio source.