Sensitivity of the astrometric technique in detecting outer planets

With the advent of optical interferometers that will be coming on line in the next decade, radial velocity searches for extrasolar planets will be complemented by high angular resolution astrometric measurements. In this paper, we explore the sensitivity of the astrometric technique, and develop an analytical understanding of the sensitivity in the regime where the orbital period is longer than the time baseline of the survey. As in an earlier paper that dealt with the radial velocity technique, our analysis of the astrometric technique utilizes both the orbital amplitude and phase.