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A&A Supplement series, Vol. 122, May I 1997, 441-445

Received June 11; accepted August 5, 1996

Optical astrometry of Benchmark radio sources

IV. New results in the southern hemisphere

E. Costa and P. Loyola

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


Optical positions relative to the International Reference Stars Catalogue (IRS), and therefore in the system of the FK5, have been obtained for the optical counterparts of 40 compact extragalactic radio sources south of tex2html_wrap_inline789. Many of these sources are being considered as possible Benchmark objects for the establishment of a quasi-inertial unified radio/optical reference frame. Precision levels as good as 0.1tex2html_wrap_inline793 in both coordinates were achieved. A comparison with VLBI radio positions available for these sources is presented. We give new evidence for the existence of an offset in the origin of right ascension between the radio and optical reference frames as defined at present.

keywords: astrometry -- reference systems

Copyright by the European Southern Observatory (ESO)