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An overview is presented of a number of astrometry and astrophysics programs based on radio sources from the Parkes 2.7 GHz catalogues. The programs cover the optical identification and spectroscopy of flat-spectrum Parkes sources and the determination of their milliarc-second radio structures and positions. Work is also in progress to tie together the radio and Hipparcos positional reference frames. A parallel program of radio and optical astrometry of southern radio stars is also under way.

Various theories have been proposed to account for the origin1,2of the low surface brightness features resembling thin shells seen in projection around some otherwise normal elliptical galaxies3. It has proved impossible to discriminate between these models owing to the lack of quantitative data on the nature of the shells. Here we present broad-band optical (B, V, R) and near-IR (J, H) photometry of one of the shells to determine their constitution and place constraints on their mode of formation. The colour indices derived suggest that the shell comprises a population of stars, perhaps bluer than the main body of the galaxy. There is no evidence for recent star formation. Our results favour dynamical models for the formation of the shells, perhaps from recent mergers of disk galaxies with the elliptical.

Accurate optical astrometry gives a position (B 1950.0) for the Large Magellanic Cloud supernova, SN1987A, relative to the FK4 system as right ascension, RA = 05 h 35min 49.95 s± 0.039s (0.21″), declination δ −69° 17′ 57.9″ ±0.27″. Differential astrometry carried out on prime-focus plates taken with the Anglo-Australian telescope indicates that the component, star 1, of Sanduleak's star Sk–69202 is within 0.05±0.13arcs of the super-nova. Here we report that this precision astrometry, together with estimates of the probability of a chance association with a fore-ground or background star, lead us to conclude that the progenitor of SN1987A was star 1 or a fainter binary companion.

The calibration of photographic sensitometers is beset with problems which can defeat photoelectric or densitometric procedures. We describe a direct and simple photographic technique using self-consistent multiple exposures which has been used to calibrate the projection sensitometers installed at the prime focus of the Anglo-Australian Telescope and at the U.K. Schmidt Telescope Unit. The method can he applied to any sensitometer and all photographic passbands. Values of relative log I for the AAT sensitometer are given for the IIIa-J emulsion with a Schott GG385 filter.