Photocentric orbits from a direct combination of ground-based astrometry with Hipparcos I. Comparison with known orbits

Abstract

Complementing the Proper Motions of Fundamental Stars catalogue by Gontcharov et al. (CDS, I-266) the photocentric orbits of some FK5/Hipparcos stars are calculated in a direct combination of the Hipparcos data with astrometric ground-based observational catalogues having epochs later than 1939. Some capabilities and limitations of this method are discussed in a comparison of our results with known orbits of Sirius, Procyon, Rasalhague, μ Cas and others. We conclude that this direct combination is an acceptable tool to discover and investigate photocentric orbits with periods from 10 to 55 years and the semi-major axis of apparent ellipses >0.08 arcsec. It is particularly suitable for pairs with large magnitude difference as well as for calculation of the preliminary orbits of new astrometric binaries which will be considered in forthcoming papers. In this paper new photocentric orbits and component masses are calculated for 4 pairs: α UMa, β LMi, δ And and ξ Aqr.