Astrometric orbits from a direct combination of ground-based catalogs with the Hipparcos catalog

A direct combination of 57 ground-based astrometric observational catalogs with the Hipparcos catalog made it possible to detect and analyze nonlinear motions of the photocenters of several tens of unresolved stellar pairs during 1938–1995. We separated these motions into the barycenter proper motions and the photocenter elliptical motions around the barycenters if the semimajor axis of the apparent ellipse in the plane of the sky is 0 .'' 08 and the period ranges from 10 to 55 years. We consider in detail six pairs for which we determined the photocenter (astrometric) orbits and the component masses for the first time: κ For (period 26.5 yr, semimajor axis of the photocenter orbit 0 .'' 26 ), δ And (52.8 yr, 0 .'' 30 ), ξ Aqr (25.5 yr, 0 .'' 11 ), 83 Cnc (32.0 yr, 0 .'' 19 ), α UMa (44.5 yr, 0 .'' 21 ), and β LMi (38.35 yr, 0 .'' 12 ). Our method is particularly efficient for a large magnitude difference between the components, for example, when searching for white dwarfs.