Statistical astrometry based on a comparison of individual proper motions and positions of stars in the FK5 and in the HIPPARCOS Catalogue

Details Statistical astrometry based on a comparison of individual proper motions and positions of stars in the FK5 and in the HIPPARCOS Catalogue Statistical astrometry based on a comparison of individual proper motions and positions of stars in the FK5 and in the HIPPARCOS Catalogue

Aug 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997esasp.402..727w&link_type=abstract

In: B. Battrick, M.A.C. Perryman and P.L. Bernacca (eds.): HIPPARCOS '97. Presentation of the Hipparcos and Tycho catalogues and

Statistics

Applications

17

Scientific paper

The wavy motions of the photocenters of undetected astrometric binaries in a sample of apparently single stars introduce `cosmic errors' into high-precision astrometry, especially into `instantaneously' measured proper motions and positions. For bright Hipparcos stars, we derive from a comparison of their proper motions given in the basic FK5 and in the Hipparcos Catalogue that the typical cosmic error in the Hipparcos proper motions of these stars is about 2 mas/year. Hence the cosmic errors are about three times larger than the measuring errors of the Hipparcos proper motions for bright stars (typically better than 0.7 mas/year), and they should therefore be taken into account in applications of the Hipparcos data. The fact that astrometric binaries are actually the most important cause of the cosmic errors are proved by the decrease of the cosmic errors with increasing distances of the stars and by the large cosmic errors in a sample of astrometric binaries which are identified as such by Hipparcos because of their non-linear motions (stars with significant g or g-dot acceleration terms). For a consistent treatment of cosmic errors in high-precision astrometry, the coherent scheme of `statistical astrometry' has been developed and is shortly summarized here. We discuss some implications of the presence of cosmic errors in the instantaneously measured Hipparcos data, and we outline the project of the FK6 where we combine the ground-based results of the basic FK5 with the Hipparcos data in order to obtain proper motions and positions of highest accuracy, taking the concepts of statistical astrometry into account.

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