Formalism and quality of a proper motion link with extragalactic objects for astrometric satellite missions

Abstract

The accuracy of the link of the proper motion system of astrometric satellite missions like AMEX and GAIA is discussed. Monte-Carlo methods were used to simulate catalogues of positions and proper motions of quasars and galaxies to test the link. The main conclusion is, that future satellite missions like GAIA may be ``self-calibrated'' by their measurements of QSOs, while additional measurements from radio stars or HST-data are needed to calibrate the less deep reaching astrometric satellite missions of AMEX type.