Abstract
ABSTRACT. The method for the reduction of astrometric plates proposed by Stock (1980) was extended to include the determination of field distortion. In a project in collaboration with the Hamburg Observatory the method was applied to two groups of plates of the Astrographic Catalogue, including part of the Paris-, Oxford-, Postsdam-, and Helsingfors zones. The results prove the existence of various types of systematic errors of the measured coordinates, principally a radial distortion which is function of the distance from the plate center, with a second component which also depends on the magnitude of the objects. Also it becomes apparent that in all of these zones the Y-axes are not perpendicular to the X-axem. The results also show that positions with a mean error of about 0.2 arcseconds can be derived from the Astrographic Catalogue. Using the AGK3 as reference system and as third epoch, the AGK2 being the second epoch, proper motions were obtained for about 3000 stars, with a mean error of approximately 3 milliarcseconds per year. These proper motions have led to the discovery of anumber of double stars of wide separation, whose physical nature is established by the coinmon proper motion. Key ct6: ASTROMETRY - CATALOGUES -POSITIONS
