Proper motions of stars in the region of the Orion association.

摘要

We present results from a proper motion study of approximately 2000 stars in the Region of the Orion Association Ia and Ib subgroups. Past studies in this region have been restricted for a number of reasons: the large angular size of the association, the lack of computational power and the high observational priority that the forming subgroups Ic and Id have received.; Our observational material spans 100 years, consisting of photographic plates taken in 1955-6 and 1992 at the McCormick Observatory and newly reduced Astrographic Catalogue positions from around 1900. The second and third epoch plates were measured on the University of Minnesota Automated Plate Scanner in two directions with two threshold levels. This provided us with an average of three position estimates per image with an image centering precision of 1-2 microns.; We reduced the measured rectangular coordinates to equatorial coordinates by the overlapping plate technique. This technique takes advantage of the extensive multiple coverage, and uses additional information on magnitude effects obtained from objective grating images.; This study will provide observations that can be used to restrict the theories of stellar association formation, runaway stars, evolutionary ages, pre-stellar gas dynamics and galactic kinematics. Through this work we illustrate the potential power of the overlapping plate technique and its application to wide field astrometry.