PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System

kappa Pegasi is a well-known, nearby triple star system. It consists of a ``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds). Using high-precision differential astrometry and radial velocity observations, the masses for all three components are determined and the relative inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/- 3.0 degrees, just over the threshold for the three body Kozai resonance. The system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with trigonometric parallax measurements.