Microarcsecond optical astrometry - an instrument and its astrophysical applications

The applications of a proposed space-based optical astrometric interferometer with a large optical bandwidth are discussed. Such an instrument would make possible an improved deflection test of general relativity, a precise and direct calibration of the Cepheid distance scale, and the determinations of stellar masses. The nominal 5-microarcsec uncertainty in the measurement of the angular separation of two stars about 90 deg apart in the sky and the projected measurement rate of 60 star pairs per day would support a range of astrophysical studies during a nominal mission life of 10 years. Means of controlling the instrument's systematic error are considered. (R.R.)