Optical positions of compact extragalactic radio sources with respect to the HIPPARCOS Catalogue

Abstract

Optical positions relative to the Hipparcos Catalogue, and therefore within the International Celestial Reference System (ICRS), have been obtained for the optical counterparts of 25 compact extragalactic radio sources (CERS) south of delta ~ +10degr . Most of these sources are being monitored as Benchmark objects for the establishment of a unified extragalactic radio/optical reference frame. Precision levels as good as 0.1arcsec in both coordinates were achieved. A comparison with VLBI radio positions available for these sources is presented. A finding chart is given for the optical counterpart of Q 1937-101. To a limiting magnitude of B ~ 20.5, no optical counterpart was found for the source 1148-671.