Astronomisches Rechen-Institut Heidelberg

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ARI-Heidelberg Mitteilungen Serie A, No. 238

Author(s): Walter, H.G., Hering, R., Lenhardt, H., de Vegt, C., Florkowski, D.R., Johnston, K.J.
Title: Accuracy Assessment of HIPPARCOS Optical and VLA Radio Positions of Stars
Source: In: Developments in Astrometry and Their Impact on Astrophysics and Geodynamics. Proc. IAU Symp. 156, Shanghai, China, 15-19 September 1992; I.I. Mueller, B. Kolaczek (eds.), Kluwer, Dordrecht, p. 377-380
Year: 1993
Abstract: Optical positions of some 30 radio stars derived from 12 months of HIPPARCOS measurements are compared with their radio positions obtained with the Very Large Array (VLA). - Once the lengths of arcs between optical and radio positions of pairs of stars are calculated the differences of the arcs are formed. They provide an estimate of the coincidence of the optical and radio emission centres.- From the comparison of optical and radio positions infinitesimal rotation angles of the HIPPARCOS frame with respect to the VLA extragalactic reference frame are determined by rigid rotations. After taking account of the relative orientation of the frames the standard deviations of the remaining residuals are approximately of the order of the VLA observation errors, thus demonstrating the reliability of the HIPPARCOS results. However, they also indicate some data noise very likely caused by the low accuracy of optical proper motions used to bridge the HIPPARCOS-radio epoch differences up to 9 years, and possible discrepancies of radio-optical emission centres of some stars.
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