We summarise the results, to date, of a long-term program of searching for flare stars in the region of open clusters selected on the basis of distance and age.

The proposal that the complex spectral line changes seen in the large amplitude β Cephei variable BW Vul resulted from a shock effect, driven by an underlying radial pulsation, was first made by Odgers (1955). Stamford and Watson (1978) examined some suitable atmospheric models for this star, which were driven by a hard subphotospheric piston under an isothermal assumption. These models displayed strong shock development and had some encouraging similarities with the BW Vul phenomenon. However, particularly because of the use of a hard piston, they were not very physically realistic. Here we discuss the results of a more sophisticated approach to this modelling problem. This modelling problem is of specific current importance because Odell’s (1981) recent observations of a variable polarization in BW Vul have renewed the debate over possible nonradial pulsations in this star. Since nonlinear effects are clearly substantial in BW Vul, it is evident that the implications of these on the observed spectral line changes should be carefully examined on a radial pulsation hypothesis, before turning to the complexities of nonlinear nonradial profile modelling.

This paper reports results from a graded shield X-ray telescope experiment flown from Mildura, Australia on 29 February 1968. The experimental equipment also included the actively collimated telescope previously described. Certain preliminary results from this flight have been described elsewhere.

Since its discovery by Haro (1952) the star H1-36 has been catalogued as a planetary nebula despite its extremely high-excitation emission-line spectrum (e.g. [Fe VII], [Ne V]) and its imposing, variable infrared excess. Because its optical spectrum resembled those of many symbiotic stars, I have persistently classified H1-36 as such. A meaningful definition of a symbiotic star would necessarily include both the high-excitation emission-line spectrum and the presence of a cool (usually M-type or Mira) giant.

Theoretical work on the radio emission from supernova remnants (SNRs) has not developed much since the pioneering work of Shklovsky (1960) and van der Laa (1962a, b). Despite agreement that the emission results from the synchrotron process, the origin of the relativistic particles and magnetic field is not clear. There are three reasonable alternatives:

1. (i) particles and field originate within the ejected material (e.g. Shklovsky 1960);

2. (ii) both field and particles originate in the compressed interstellar medium (e.g. van der Laan 1962a);

3. (iii) the field is interstellar but the particles are from the ejecta (as outlined by van der Laan 1962b).

Pulsars display a complicated pattern of amplitude variations. The scale of variations range from months through hours to sub-milliseconds. The purpose of this note is to present polarization data for CP 1919 and intensity distribution data for PSR 0833—45 which are relevant to pulse-to-pulse variations and the variation over periods of hours respectively.

A redistribution function R(x, x′)dx dx′ is defined as the probability that a photon with frequency between x and x + dx will be absorbed by an elemental atmosphere which then emits another photon the frequency of which lies in the range from x′ to x′ + ax′. The frequencies x and x′ are measured from the central frequency νo of the spectral line in units of the Doppler width Δ The particular functional form taken by R(x, x′) in this discussion will be given by

where α represents the broadening of the spectral line in units of the Doppler width while the function H(o, z) is defined by

the Voigt function. The function defined by means of equation (1) is one of that class of redistribution functions which combines natural and Doppler broadening. Therefore, it should be expected that any results obtained using this particular redistribution function will exhibit certain features characteristic of this type of scattering.

Ultra-high resolution hydrodynamic simulations using 10243 grid points are performed of a very large supernova burst in a forming galaxy, with properties similar to those inferred for Lyman Break Galaxies (LBGs). Explosions produce kpc-sized expanding hot bubbles enclosed by cool, dense shells, and the engulfed gas is polluted with freshly-synthesised heavy elements. We show that the resultant inhomogeneous mixing produces a large spread ([Fe/H] ≈ –1 to –5) of metallicities, which affects the subsequent galactic chemical evolution and leaves its imprint on metal-poor stars. By combining a spectral synthesis model with the numerical results, we predict Lyα emission from such galaxy at z = 3. We find that the simulated galaxy, whose peak star formation rate is ≈200 M⊙ yr–1, produces a Lyα luminosity Lα = 9.7 × 1042 erg s–1. This value favorably matches the observed one, but some discrepancies are left for the Lyα line width, the metallicity, and X-ray properties. Since the results of the simulation is applicable only at the very early epoch of the galaxy formation, the metallicity is still lower than that of LBGs. However, the analysis presented here demonstrates a way to enable a systematic comparison with observational data.

It is concluded that LBGs are optimal objects to scrutinise the early self-enrichment in forming galaxies. In the future, the predicted bubbly structure carved by SNe may be directly detected by high resolution observations with JWST.

We present results of VLBI monitoring observations of the blazars detected by ground-based TeV gamma-ray telescopes. Preliminary results have shown that the apparent speeds of the parsec-scale jet features in these sources are predominantly subluminal, and significantly slower than those in the GeV-peaked (EGRET) gamma-ray blazars. Here we add results from additional sources and additional epochs that increase the statistical significance of this comparison. These slower speeds may indicate rapid deceleration of the jets in TeV blazars between the TeV gamma-ray emitting scales and VLBI scales.

We use high-resolution n-body/SPH simulations to study the hydrodynamical interaction between the Large Magellanic Cloud and the hot halo of the Milky Way. We investigate whether the ram-pressure acting on the gaseous disk of the satellite can explain the peculiarities observed in the Hi distribution and the location of the recent star formation activity.

The 2 degree Field (2dF) galaxy redshift survey will involve obtaining spectra of approximately 2.5 105 objects which have previously been identified as galaxy candidates on morphological grounds. Included in these spectra should be about ten gravitationally-lensed quasars, all with low-redshift galaxies as deflectors (as the more common lenses with high-redshift deflectors will be rejected from the survey as multiple point-sources). The lenses will appear as superpositions of galaxy and quasar spectra, and either cross-correlation techniques or principal components analysis should be able to identify candidates systematically. With the 2dF survey approximately half-completed it is now viable to begin a methodical search for these spectroscopic lenses, and the first steps of this project are described here.

We re-evaluate the outer edge of orbital stability for possible exomoons orbiting the radial velocity planet discovered in the HD 23079 system. In this system, a solar-type star hosts a Jupiter-mass planet in a nearly circular orbit in the outer stellar habitable zone. The outer stability limit of exomoons is deduced using N-body and tidal migration simulations considering a large range of initial conditions, encompassing both prograde and retrograde orbits. In particular, we extend previous works by evaluating many values in the satellite mean anomaly to identify and exclude regions of quasi-stability. Future observations of this system can make use of our results through a scale factor relative to the currently measured minimum mass. Using a constant time lag tidal model (Hut 1981), we find that plausible tidal interactions within the system are insufficient to induce significant outward migration toward the theoretical stability limit. While current technologies are incapable of detecting exomoons in this system, we comment on the detectability of putative moons through Doppler monitoring within direct imaging observations in view of future research capacities.

A complete orbital light-curve of V2051 Oph in the IR H band is presented, together with a second eclipse in the J band. Simultaneous Rc band data were obtained. Eclipse depths in Rc, J and H are 1.8 mag, 1.0 mag and 0.8 mag respectively. No evidence for ellipsoidal variations due to the secondary was seen and constraints on the secondary are discussed.

From the Lyon-Meudon Extragalactic Database (LEDA) we constructed a sample of 27000 galaxies with radial velocities smaller than 15 000 kms−1. From this first sample we selected the 5683 largest galaxies, which constitute a sample complete up to the diameter limit D25 = 1·6′. This sub-sample has been used to search for the most populated plane. The result is that the plane defined by the pole (l = 52°; b= 16°) contains twice as many galaxies as would be found for randomly distributed galaxies. This plane is not far from the supergalactic plane. The distribution of galaxies in this plane has been studied by using the radial velocity as an estimate of the distance. An excess of galaxies appears at a distance of about 70 Mpc. We discuss the reality of this density enhancement which could result from selection effects.

Observations of the Pluto-Charon system using the Hubble Space Telescope are soon to provide another test of the modern Laplacian theory of solar system origin. According to this theory, Pluto, Charon and Neptune’s moon Triton are condensed remnants of the gas ring which was shed by the proto-solar cloud at Neptune’s orbit, and from which Neptune formed. Each body should have the same bulk chemical composition provided that the influence of secondary events such as physical collision can be neglected. Here we report a model for the time-dependent, surface-catalysed production of CH4, solid carbon C(s) and CO2 within the outer layers of the proto-solar cloud. This model is used to determine the condensate mix which best fits the Voyager 2 spacecraft measurements of Triton’s mean density. We suggest that Triton is a chemically homogeneous structure consisting, by mass, of 44.2% anhydrous rock, 2.1% graphite, 33.0% water ice and 20.7% dry ice (i.e., solid CO2 ice, of which a fraction nearly 2/3 is present as the clathrate hydrate CO2·5.75 H2O). On the basis of this composition, the individual mean densities of Pluto and Charon are predicted to be 2.02 ± 0.02 g/cm3 and 1.94 ± 0.02 g/cm3, respectively, assuming a mean surface temperature of 35 K. The mean density of the combined system is predicted to be 2.01 ± 0.02 g/cm3.

The Fault Diagnosis Expert System for the Australia Telescope analyses ~12000 items of monitor data every minute that report the health and stability of specific components and signal pathways in the array. These data are divided into signatures which are matched against signatures of known failure modes to diagnose problems with the array. Knowledge about many of the failures is acquired by generating them in earlier tests. The system keeps a six-hour history of the detailed behaviour of all monitor data as well as the visibilities. It archives the data in half-hour intervals, characterising the interval with a small set of robust statistical estimators. An interactive graphical user interface allows the simultaneous display of twenty-four histories of either the 6-hour data or one week of the characterised data, together with options for plotting one history against another and for calculating their robust regression.

Observations have been made, using the Epping 4-m radio telescope, of emission from the J = 1-0 transition of CO (115 GHz) towards the Southern Coalsack. The half-power beam-width was 2′.7 arc and the radial velocity resolution was 0.07 km s−1. The line was found to be distributed with varying intensity over an area of 63′ × 36′ arc. The mean radial velocity was −5.8 km s−1 and mean half-intensity linewidth 1.18 km s-1. A typical line temperature was 8 K with maxima exceeding 12 K. The results suggest a stable dark cloud region with no significant evidence of systematic motions.

Expressions for the physical structure of a sequence of two zone polytropic stellar models, based on composite analytical solutions of the Lane-Emden equation with indices n = 1 and n = 5, hâve been determined. The coefficients of vibrational stability for radial oscillations of this sequence of models have also been calculated and it is found that increasing the extent of the n = 5 outer zone has a stabilizing effect.

The following are brief summaries of recent observational investigations of SN 1987A by ESO staff and their collaborators, which were reported at the Conference.

The Sun being a highly ionized gas, the basic physical quantities most needed for understanding solar phenomena are temperature, pressure (or density), velocity and magnetic field, together with their variations in space and time. The general aim at Culgoora is to secure observations from which these quantities may be derived (insofar as is practicable) simultaneously over extended solar regions. To do this has involved the development and use of filters of high spectral and spatial resolution, the study of atmospheric seeing and ways of securing high-resolution observations, and the study of methods of analysing observations to yield the physical quantities needed.