Limits to Tertiary Astrometric Companions in Binary Systems

The Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES) has monitored 37 sub-arcsecond binary systems to determine whether their Keplerian orbits are perturbed by faint astrometric companions to either star. Software has been developed to evaluate the regions in a companion mass-period phase space in which the PHASES observations can exclude the possibility of face-on orbit perturbations. We present results for 8 systems for which astrometric companions with masses as small as those of giant planets can be excluded