Asteroids

The surface albedo distributions found with early post-COSTAR FOC observations were checked by Albrecht against later, much more extensive, FOC observations obtained by Stern and Tholen. Good agreement was established. Work on the mapping of the surface of the asteroid Vesta continued. While the results are quite promising, the early observations are not totally conclusive owing to instrumental problems and insufficient coverage. More observations will be obtained (with Hainaut and Dumas in Hawaii, and Schober in Graz).

HII regions

HST FOS spectra have been obtained by Rosa, Walsh and Och for a number of dense condensations and filaments embedded in the more tenuous phase of the Orion HII region. The diagnostic diagrams constructed using a large suite of emission lines that can be measured at 1500-8500 Å indicate a considerable range of densities and electron temperatures, not seen before in ground-based optical spectra. A sizable fraction of the emission in low ionisation stages happens at or above the critical densities, which can be as high as 10⁶/cm³. Abundance determinations based solely on assumptions valid for homogeneous HII region models, i.e. smooth distributions of Te and Ne combined with rather low Ne values (<10³) are therefore suspected to contain systematic errors. This is likely to be the source of the long-standing problem of discrepant O/H determinations for the solar neighbourhood, stellar values being about a factor two higher than values determined from HII regions.

A method has been developed by Och, Rosa, Lucy and Walsh to produce photoionisation models of inhomogeneous HII regions. The code, based on the Monte Carlo technique, provides a self- consistent way to treat the energy conservation and the radiation transport problem in arbitrary geometries and inhomogeneous density distributions. The code has been fully tested against the results of the major homogeneous model codes available in the literature. Now it is being applied to stochastic inhomogeneous cases matching the observational results for the Orion nebula. It is hoped to develop scaling laws and techniques that will allow one to derive more reliable chemical abundances for remote HII regions that cannot be studied at the superb spatial resolution obtained with HST on the Orion nebula.

Active galaxies

Fosbury, with Morganti and Osterloo (ATNF), Tadhunter (Sheffield), Danziger (Trieste), di Serego Alighieri (Arcetri) and Siebert and Brinkmann (MPE), have continued the multi- wavelength studies of a complete sample of southern hemisphere 2 Jy radio sources by using Monte Carlo techniques to investigate and quantify the effects of beaming on the sample properties in the radio band. They have also extended their original optical and radio observations into X-ray using the ROSAT satellite. This sample is proving of unique value in elucidating the physical differences between the Fanarof-Riley class I and class II radio sources.

A deep X-ray image of the radio galaxy Centaurus A was obtained with ROSAT's High Resolution Imager by Doebereiner and Junkes (MPE), Wagner (Heidelberg), Zinnecker (Potsdam), Fosbury, Fabbiano (CfA) and Schreier (STScI). This resolves most of the knots in the X-ray jet in both the longitudinal and lateral directions and detects a new X-ray component on the counter-jet side, which probably represents hot gas compressed by the inner SW radio lobe.

Studies of the physical properties of radio galaxies - out to the highest redshifts - are being revolutionised by the availability of high resolution imaging data from HST and imaging and spectro-polarimetry from the 10 m Keck telescopes. Fosbury and Hook, in collaboration with di Serego Alighieri (Arcetri), Cimatti (Livermore/Arcetri), Perez-Fournon (IAC) Villar-Martin, Tadhunter, Shaw and Clark (Sheffield), Binette (Lyon), Cohen and Ogle (Caltech), Tran (Lick), Goodrich (Keck), Barthel and Hes (Groningen), Morganti and Killeen (ATNF) and Siebert (MPE), are carrying out a programme to disentangle and measure the different radiating components that characterise these sources. Observations underway with ISO at mid- and far-IR wavelengths and with the IRAM and JCMT at mm and sub-mm wavelengths will further constrain the stellar population models and measure the thermal radiation from the cool dust that is responsible for much of the scattered UV light.

Interstellar medium

Two high resolution spectroscopic programmes by Caulet, in collaboration with Smith (GSFC) and Newell (Pomona) study, in three dimensions, the dynamic interstellar medium (ISM) of the Superbubble LMC2 in the Large Magellanic Cloud. Using CASPEC on the 3.6 m at La Silla, TiII and CaII absorption line components were detected along the lines of sight of seven LMC OB supergiants towards LMC2. This is the first time that extragalactic TiII has been clearly detected, and that IS absorbing clouds are recognised towards a superbubble. Using the GHRS on HST in the UV, the same seven star lines of sight probe the gas over a larger temperature range (100 K to 100 000 K). Many absorption lines from the ions SII, SiII and CIV, which are tracers of warm and hot gas, are detected, most coincident with TiII and/or CaII absorbing clouds. From the ion column densities and decomposition of published 21 cm HI emission line profiles, abundance and depletion determinations in the various layers of LMC2 (disc-halo) are calculated.

Quasar absorption lines

Caulet, in collaboration with Lowenthal (Lick), Hogan (Seattle), Green (NOAO), Woodgate and Brown (GSFC) Foltz (Steward), McCaugrean (Heidelberg) and Athey (Pomona), have completed the Fabry-Perot optical imaging survey of Ly alfa emission from the QSO damped Ly alfa systems that have been postulated to be large galactic discs undergoing intense star formation activity at the time of galaxy formation. With their Ly alfa detection of the first galaxy near a damped absorber at z=2.3 (towards the QSO PHL 957), it was realised that damped systems are associated with groups of galaxies. Hence the technique of Fabry-Perot imaging tuned to the redshift of distant QSO absorbers could be used to find high redshift clusters containing galaxies at different states of formation. In order to test the scenario of starbursts occurring in dusty regions, they have conducted an IR imaging survey in the H, J and K bands to search for [OII] or H alfa emission from the QSO damped Lya systems. Many faint galaxies are detected, some near the QSO lines of sight. The candidates need to have spectroscopic identification, possibly in the IR, requiring large telescopes such as the 10 m Keck, the 8 m VLT in the near future, or the use of STIS and NICMOS on HST.

Data analysis and computer science

Extensive use of the archive is being made by Lucy, Hook, Pirenne and Prieto (MPE) for the purpose of HST/ground-based data fusion and for routine application of point source function (PSF) subtraction to QSOs. Several areas in computer science and data analysis of particular relevance to the HST and its science data archive are being developed. Further applications of the basic iterative deconvolution code are being developed for crowded field photometry and data combination, especially in polarimetry and 3-D spectroscopy. Albrecht, Pirenne and Micol are investigating methods to make computational capabilities available through the WWW in a transparent and platform- independent manner. Several prototype tools have been implemented using Java and Javascript. The goal is to make HST-related calibration capability available to off-site users with minimum impact on the ST-ECF computer infrastructure, while retaining full control over the software.