We present photometric observations of six radio-loud quasars that were detected by the COMPTEL gamma-ray telescope. The data encompass seven wavebands in the optical and near infrared. After correction for Galactic extinction, we find a wide range in optical slopes. Two sources are as blue as optically-selected quasars, and are likely to be dominated by the accretion disc emission, while three others show colours consistent with a red synchrotron component. We discuss the properties of the COMPTEL sample of quasars, as well as the implications our observations have for multiwavelength modelling of gamma-ray quasars.

AGN with the so-called 'double-double' radio structure have been interpreted as restarted AGN where the inner structure is a manifestation of a new phase of activity which happened to begin before the outer radio lobes resulting from the previous one had faded completely. The radio galaxy 1245+676 is an extreme example of such a double-double object — its outer structure, measuring 970 h−1 kpc, is five orders of magnitude larger than the 9.6 h−1 pc inner one. We present a series of VLBI observations of the core of 1245+676 which appears to be a compact symmetric object (CSO). We have detected the motion of the CSOs lobes, measured its velocity, and inferred the kinematic age of that structure.

We present a new procedure for photometric parallax estimation. The data for 1236 stars provide calibrations between the absolute magnitude offset from the Hyades main-sequence and the ultraviolet-excess for eight different (B–V)0 colour-index intervals, (0.3 0.4), (0.4 0.5), (0.5 0.6), (0.6 0.7), (0.7 0.8), (0.8 0.9), (0.9 1.0) and (1.0 1.1). The mean difference between the original and estimated absolute magnitudes and the corresponding standard deviation are rather small, +0.0002 and ±0.0613 mag. The procedure has been adapted to the Sloan photometry by means of colour equations and applied to a set of artificial stars with different metallicities. The comparison of the absolute magnitudes estimated by the new procedure and the canonical one indicates that a single colour–magnitude diagram does not supply reliable absolute magnitudes for stars with large range of metallicity.

We derive an updated, analytic formula for the gravitational radius, rg, of an irradiated, thin disk. For such a disk, the region outside the gravitational radius will produce a thermal wind, while the region interior to the gravitational radius will be stable. We find that rg ≈ 1.4 (M*/M⊙)/(T0/104K) AU. The value of 1.4 AU is approximately one fifth of currently used values.

The analysis uses the adiabatic approximation. We argue that the same formula applies for the non-adiabatic, isothermal case.

The five-minute oscillations in the Sun have provided a wealth of information about the solar interior. After many attempts, positive detections of similar oscillations in solar-type stars have now been made. This review discusses the properties of solar-like oscillations, the methods used to observe them, and the results on individual stars. We conclude that the study of solar-like oscillations from the ground and space has an exciting future.

The abundance of the neutron-rich magnesium isotopes observed in metal-poor stars is explained quantitatively with a chemical evolution model of the local Galaxy that considers — for the first time — the metallicity-dependent contribution from intermediate mass stars. Previous models that simulate the variation of Mg isotopic ratios with metallicity in the solar neighbourhood have attributed the production of 25Mg and 26Mg exclusively to hydrostatic burning in massive stars. These models match the data well for [Fe/H] > –1.0 but severely underestimate 25,26Mg/24Mg at lower metallicities. Earlier studies have noted that this discrepancy may indicate a significant role played by intermediate mass stars. Only recently have detailed calculations of intermediate mass stellar yields of 25Mg and 26Mg become available with which to test this hypothesis. In an extension of previous work, we present a model that successfully matches the Mg isotopic abundances in nearby Galactic disk stars through the incorporation of nucleosynthesis predictions of Mg isotopic production in asymptotic giant branch stars.

We investigate the production of aluminium and magnesium in asymptotic giant branch models covering a wide range in mass and composition. We evolve models from the pre-main sequence, through all intermediate stages, to near the end of the thermally-pulsing asymptotic giant branch phase. We then perform detailed nucleosynthesis calculations from which we determine the production of the magnesium and aluminium isotopes as a function of the stellar mass and composition. We present the stellar yields of sodium and the magnesium and aluminium isotopes. We discuss the abundance predictions from the stellar models in reference to abundance anomalies observed in globular cluster stars.

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 H0 = 100 h km s−1 Mpc−1 and q0 = 0.5.

We investigate the effect of duplicity on stellar yields of carbon, nitrogen, and oxygen. Populations of single and binary stars are modelled and the yields calculated for the whole population. The effects of explosive nucleosynthesis in novae and supernovae are included but by artificially removing these effects from our populations we determine the influence of a binary companion on asymptotic giant branch yields of the CNO elements.

We present high resolution spectra (0.7 Å/pix) of the GPS source 4C 12.50 with large spectral coverage (˜4500 Å) taken with the 4.2 m William Herschel Telescope, La Palma. The slit was aligned along PA 160° to include the nucleus and emission line region to the NW. An asymmetric halo extending 20 kpc NW and 12 kpc SE from the nucleus is clearly seen. At the position of the nucleus we observe unusually broad forbidden emission line components (broadest component: FWHM ˜ 2000 km s−1), blue shifted by up to 2000 km s−1 with respect to the halo of the galaxy and HI absorption. We interpret this as material in outflow. We measure E(B–V) = 1.44 for the broadest, most kinematically disturbed component, corresponding to an actual Hβ flux 130 times brighter than that measured. We calculate an upper limit for the mass of the line emitting gas of order 106 M⊙ for both the intermediate and broad components. Our results are consistent with 4C 12.50 being a young radio source.

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.

Infrared observations of nova light curves reveal that classical novae form grains in the expanding shells, ejected into the interstellar medium as a consequence of a violent outburst. Such grains contain nucleo-synthetic fingerprints of the nova explosion. In this paper, we analyse different isotopic signatures expected to be present in nova grains on the basis of detailed hydrodynamic calculations of CO and ONe novae and compare them with recent determinations of presolar nova grains from the Acfer 094 and Murchison meteorites.

We have obtained long slit spectra of 3C 67 and 3C 277.1 with the HST/STIS spectrograph. We present our preliminary results on the diagnostic emission line ratios along the radio source axes in 3C 67 and 3C 277.1.

We describe the first distributed data implementation of the perspective shear-warp volume rendering algorithm and explore its applications to large astronomical data cubes and simulation realisations. Our system distributes sub-volumes of 3-dimensional images to leaf nodes of a Beowulf-class cluster, where the rendering takes place. Junction nodes composite the sub-volume renderings together and pass the combined images upwards for further compositing or display. We demonstrate that our system out-performs other software solutions and can render a 'worst-case' 512 × 512 × 512 data volume in less than four seconds using 16 rendering and 15 compositing nodes. Our system also performs very well compared with much more expensive hardware systems. With appropriate commodity hardware, such as Swinburne's Virtual Reality Theatre or a 3Dlabs Wildcat graphics card, stereoscopic display is possible.

We discuss possible stellar origins of short-lived radioactive nuclei with meanlife τ ≤ 100 Myr, which were shown to be alive in the Early Solar System (ESS). We first review current ideas on the production of nuclides having 10 ≤ τ ≤ 100 Myr, which presumably derive from the continuous interplay of galactic astration, nucleosynthesis from massive supernovae and free decay in the interstellar medium. The abundance of the shorter lived 53Mn might be explained by this same scenario. Then we consider the nuclei 107Pd, 26Al, 41Ca and 60Fe, whose early solar system abundances are too high to have originated in this way. Present evidence favours a stellar origin, particularly for 107Pd, 26Al and 60Fe, rather than an in situ production by energetic solar particles. The idea of an encounter (rather close in time and space) between the forming Sun and a dying star is therefore discussed: this star may or may not have also triggered the solar formation. Recent nucleosynthesis calculations for the yields of the relevant short-lived isotopes and of their stable reference nuclei are discussed. Massive stars evolving to type II supernovae (either leaving a neutron star or a black hole as a remnant) seem incapable of explaining the four most critical ESS radioactivities in their observed abundance ratios. An asymptotic giant branch (AGB) star seems to be a viable source, especially if of relatively low initial mass (M ≤ 3 M⊙) and with low neutron exposure: this model can provide a solution for 26Al, 41Ca and 107Pd, with important contributions to 60Fe, which are inside the present uncertainty range of the 60Fe early solar system abundance. Such a model requires that 26Al is produced substantially on the AGB by cool bottom processing. The remaining inventory of short-lived species in the solar nebula would then be attributed to the continuous galactic processing, with the exception of 10Be, which must reflect production by later proton bombardment at a low level during early solar history.

In this paper I examine the use of optical and UV spectral diagnostic ratios to distinguish between gas which is locally shock-excited by the interaction with a jet and that which is photoionised by the central engine. In many cases key UV lines remain unobserved except in the case of high redshift radio galaxies. However, in one case, the nearby GPS galaxy NGC1052, UV data was obtained with the FOS. This object shows LINER characteristics at optical wavelengths, but has a rich coronal-line spectrum in the UV. We conclude that jet-driven shocks tend to evolve from shock-excited to photoionised later in their evolution.

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.

We present new results on the evolution and nucleosynthesis in rotating AGB stars. We analyse the role of the gradient of mean molecular weight in the mixing process and show that neglecting this component induces a potentially strong third dredge-up. We also quantify the impact of rotation on the structure and conclude that the effects of rotation (1) mainly concern the inner, fast rotating regions of the stars and (2) are relatively weak as long as rotational mixing does not induce a deep third dredge-up. We also focus our investigations on the s-process nucleosynthesis and show that rotational mixing tends to inhibit the production of s-elements. This results from the contamination of the 13C-rich layers responsible for the neutron production by the poisonous 14N. Our calculations also indicate that the distribution of s-process elements depends sensitively on the magnitude of the diffusion coefficient. These results suggest that rotational mixing is not the main mechanism responsible for the production of s-elements in AGB stars, but that it can influence, and in particular reduce, the final enrichment in s-elements.

Presolar graphite contains a 22Ne-rich component called Ne-E(L). Noble gas studies on graphite aggregates and single grains have shown that although a dominant source of the 22Ne is 22Na, 22Ne in the He-shell of asymptotic giant branch stars have also contributed to the Ne-E(L). In addition to novae that have been considered to be a possible source of 22Na, supernovae are a likely source as well. Krypton isotopic ratios of the separates indicate that part of graphite formed in low-mass (≤3 M⊙) asymptotic giant branch stars of low metallicity (Z ≤ 0.006).

GPS and CSS radio sources are the objects of choice to investigate the evolution of young radio-loud AGN. Previous investigations, mainly based on number counts and source size distributions, indicate that GPS/CSS sources decrease significantly in radio power when evolving into old, extended objects. We suggest this is preceded by a period of increase in radio luminosity, which lasts as long as the radio source is confined within the core-radius of its host galaxy. We have selected a sample of nearby compact radio sources, unbiased by radio spectrum, to determine their luminosity function, size distribution, dynamical ages, and emission line properties in a complete and homogeneous way. First results indicate that the large majority of objects (>80%) exhibit classical GPS/CSS radio spectra, and show structures consistent with them being compact double or compact symmetric objects. This sample provides an ideal basis to further test and constrain possible evolution scenarios, and to investigate the relation between radio spectra and morphologies, orientation and Doppler boosting in samples of young radio-loud AGN, in an unbiased way.