Gl White

A Radio-Continuum Study of the Magellanic Clouds

The far-infrared (42.5-122.5 μm, hereafter FIR) and the 6.3 cm radio continuum map of the LMC are found closely correlated, in the sense of an overall coincidence of peaks in the two maps and a strong resemblence around giant star formation regions (30 Doradus, the bar, etc.). The FIR disk and the 6.3 cm disk have similar sizes. No gradient in the FIR-to-6.3 cm brightness ratio with increasing galactic radius is found. Statistical studies reveal that the local point-by-point correlation between the two maps is comparably strong as the global FIR/radio correlation for gas-rich galaxies.

An observational program for a unified optical-radio reference frame

An observational pilot program is described which provides a first step towards the construction of an inertial extragalactic reference frame from optical and radio measurements. Candidate objects will be selected from extragalactic compact radio sources which display optical counterparts. Galactic radio stars will be secondary reference objects. The reference frame will be defined by the radio positions of the extragalactic objects. Based on a coordinated effort in both hemispheres, a global homogeneous net of about 400 quasars and 100 radio stars is expected to result from a five year campaign.

Commission 24: Photographic Astrometry

An investigation performed during 1995 throughout the commission showed that the main fields of activity of the members of our commission are much more wider than its title would indicate. The overlap is huge with Commission 8, and many of the topics, such as space astrometry, CCD or radio astrometry, are clearly relevant of both commissions.

A Counterjet in the Nucleus of Centaurus A

Centaurus A (NGC 5128) is the nearest giant radio galaxy. It is a Fanaroff-Riley type 1 (low luminosity) radio source, but the compact radio source in the nucleus is strong enough that VLBI imaging has been possible with both the SHEVE array and the VLBA at several frequencies. These observations have detected a sub-parsec scale counterjet. This shows that jet formation in at least some FR I sources is intrinsically two-sided over very small distances and the radio jets in Centaurus A are probably only moderately relativistic. We also find evidence that the center of activity in Centaurus A is partially obscured by a disk or torus of dense plasma. We observed Centaurus A at 8.4 GHz with a global (SHEVE+VLBA) array in October 1993. The resulting image is shown in figure la. The brightest peak corresponds to the inverted-spectrum core (as determined from nearly-simultaneous 4.8 and 8.4 GHz SHEVE images; Jauncey et al. 23 R. Ekers et al. (eds.), Extragalactic Radio Sources, 23-24.