Masses and Orbits of Extrasolar Planets: Preparation of Astrometric Observing Programs

Astrometry is the most powerful technique to determine dynamical masses and orbital parameters of extrasolar planets. The careful selection and characterization of reference stars is crucial for the success of any astrometric program. The best reference stars for NASA's Space Interferometry Mission (SIM) are distant K giants. The first sub-stellar companion to a K giant was recently detected serendipitously in a radial-velocity survey aimed at defining the SIM grid star strategy.