| dc.description.abstract | Optical positions relative to the Hipparcos Catalogue (ESA 1997) have been obtained for the optical
counterparts of 28 faint (B 20−23) southern compact extragalactic radio sources (CERS). Most of these sources
are not adequately observable (or simply not visible) by means of direct photography with a conventional wide-
eld telescope, so the positions were determined using a multi-step procedure involving CCD and photographic
observations. This method responds both to the need of attaining small positional errors and the need to refer the
positions to a standard astrometric system. Estimated precisions as good as 60 mas were achieved. For 13 of the
above objects, namely 0214−522, 0614−349, 0700−465, 0823−500, 1120−274, 1143−331, 1347−218, 1349+027,
1817−254, 1829−718, 1920−211, 2139+028 and 2211−388, we are proposing a new optical identi cation. A
comparison with VLBI radio positions available for these sources is presented. The residuals obtained are in most
cases consistent with the precision of our optical data, and provide an evaluation of these faint objects as possible
radio/optical frame link sources (or their identi cation as astrophysically interesting astrometric outliers). Fifteen
of the CERS observed are either de ning or candidate ducial objects of the present realization of the 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. | |
