Astronomisches Rechen-Institut Heidelberg

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ARI-Heidelberg Mitteilungen Serie A, No. 145

Author(s): Walter, H.G.
Title: Very-Long-Baseline Interferometry Applied to Fundamental Astrometry
Source: In: Very Long Baseline Interferometry Techniques, Proc. Conf., Toulouse, France, 31 August - 2 September 1982; Centre National d'Etudes Spatiales, Capedues-Editions, Toulouse, p. 173-181
Year: 1983
Abstract: The definition of a non-rotating reference frame and its representation by a suitable set of fiducial points constitute one of the basic problems in fundamental astronomy. After the discovery of the extragalactic nature of radio emitting quasars and the development of the technique of Very-Long-Baseline Interferometry (VLBI) for precise position determination these radio sources began to qualify as fiducial points. In this respect VLBI becomes instrumental to the establishment of a kinematically defined frame of reference. Starting out from the VLBI observables and their information content the fundamental quantities for positional astronomy are derived. On these grounds the concept of a reference frame based on extragalactic radio sources is described and the currently available astrometric data on objects radiating at radio frequencies are inspected in terms of spatial distribution, flux and source structure. Methods for relating radio source coordinates to stellar coordinates and the problem of frame densification are discussed in connection with the optical counterparts of the sources and with radio stars.
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