Interferometry and spectroscopy of sigma Orionis

Using these measurements, we spatially resolve the orbit of the close spectroscopic binary (Aa,Ab) for the first time and present a revised orbit for the wide pair (A,B). Combining the visual orbits with previously published radial velocity measurements and new radial velocities measured at CTIO, we derive dynamical masses for the three massive stars in the system of M_Aa_=16.99+/-0.20M_{Sun}_, M_Ab_=12.81+/-0.18M_{Sun}_, and M_B_=11.5+/-1.2M_{Sun}_.

The inner and outer orbits in the triple are not coplanar, with a relative inclination of 120{deg}-127{deg}. The orbital parallax provides a precise distance of 387.5+/-1.3pc to the system. This is a significant improvement over previous estimates of the distance to the young {sigma} Orionis cluster.