EDP Sciences
Free access
Volume 381, Number 1, January I 2002
Page(s) 13 - 20
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20011404

A&A 381, 13-20 (2002)
DOI: 10.1051/0004-6361:20011404

CCD astrometry of faint compact extragalactic radio sources. III.

E. Costa

Departamento de Astronomía, Universidad de Chile, Casilla 36-D Santiago, Chile

(Received 27 June 2001 / Accepted 2 October 2001)

Optical positions relative to the Hipparcos Catalogue (ESA 1997) have been obtained for the optical counterparts of 38 faint ( $B\sim20{-}24$) southern compact extragalactic radio sources (CERS). Many of these sources are not detectable - or their coordinates not adequately measurable - by means of direct photography with a wide-field telescope, so the positions were determined using a multi-step procedure involving CCD and photographic observations. This method responds both to the requirement of attaining small positional errors, and the need to refer the positions to a standard astrometric system. Estimated precisions as good as 50 mas were achieved. For 16 of the above objects we are proposing a completely new optical identification or providing a revised finder. A comparison of our optical positions with available VLBI radio positions is presented. The residuals obtained are in most cases consistent with the precision of our optical data, and provide an evaluation of these CERS as radio/optical frame link sources (or their identification as astrophysically interesting astrometric outliers). Twenty nine of the CERS observed are either defining or candidate fiducial objects of the present International Celestial Reference System (ICRS, Ma et al. 1998), so the optical data we have obtained for them is potentially useful to help mantain and possibly improve the current link of the Hipparcos reference frame to the ICRS.

Key words: astrometry -- reference systems

SIMBAD Objects

© ESO 2002