Optical counterpart positions of extragalactic radio sources and connecting optical and radio reference frames

摘要

We discuss the results of an investigation of astrometric positionsof extragalactic radio sources from a list for the InternationalCelestial Reference Frame. About 300fields around extragalacticradio sources were observed during the years2000-2003. Theobservations were performed mainly using two telescopes equipped withCCD cameras at TUG, Turkey (Russian-Turkish Telescope- RTT150)and at YAO (1m telescope), (Kunming, China). The mean accuraciesof the measured positions are 38mas in right ascension and35mas in declination. Acomparison between the measuredoptical positions determined using the UCAC2catalog and the radiopositions from the current ICRF shows that the overall optical-minus-radio offsets are -4 and +15mas for right ascension anddeclination, respectively. The formal internal errors of these meanoffsets are 4mas. The results of optical positions with respectto the reference catalogue 2MASS are also given. Asearch for arelation between optical and radio reference frames indicates that theorientation angles are near zero within their accuracy of about5mas. The link accuracy becomes 3mas when our observationsare combined with other studies.Key words: astrometry - reference systems