High-precision astrometry of crowded fields by interferometry

The Orbiting Stellar Interferometer (OSI) is a space based interferometer capable of making astrometric measurements with 2 - 5 uas accuracy. Typical astrometric observations have one target star within the instrument's instantaneous field of view. The presence of other stars within this field will introduce systematic errors in the measurement. In this paper we present a method of accurately determining the position of multiple stars in the field of view. This method is an extension of the conventional synthesis imaging techniques that will be used for OSI. Astrometric measurements in these crowded field will be extremely useful in studying the dynamics of globular clusters and to make measurements in the direction of the center of the galaxy.