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

κ Pegasi is a well-known, nearby triple star system. It consists of a "wide" pair with semimajor axis = 235 mas, one component of which is a single-line spectroscopic binary (semimajor axis = 2.5 mas). Using high-precision differential astrometry and radial velocity observations, the masses for all three components are determined and the relative inclination between the wide and narrow pairs' orbits is found to be 43.°8 ± 3.°0, just over the threshold for the three-body Kozai resonance. The system distance is determined to be 34.60 ± 0.21 pc and is consistent with trigonometric parallax measurements.