Orbits, Distance, and Stellar Masses of the Massive Triple Star Sigma Orionis

TL;DR

This study uses interferometry and radial velocities to precisely measure the orbits and masses of the sigma Orionis triple star system, revealing non-coplanar orbits and refining the system's distance.

Contribution

First spatially resolved orbit of the close binary in sigma Orionis and a revised orbit for the wide pair, leading to accurate stellar masses and a precise distance estimate.

Findings

Dynamical masses of the three stars: 16.99, 12.81, and 11.5 solar masses.

Inner and outer orbits are not coplanar, with a 120-127 degree inclination.

Distance to sigma Orionis system is 387.5 parsecs, more precise than previous estimates.

Abstract

We present interferometric observations of the sigma Orionis triple system using the CHARA Array, NPOI, and VLTI. 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 +/- 0.20 Msun, M_Ab = 12.81 +/- 0.18 Msun, and M_B = 11.5 +/- 1.2 Msun. The inner and outer orbits in the triple are not coplanar, with a relative inclination of 120-127 deg. The orbital parallax provides a precise distance of 387.5 +/- 1.3 pc to the system. This is a significant improvement over previous estimates of the distance to the young sigma Orionis cluster.