Dynamical parallax of σ Ori AB:: mass, distance and age

The massive OB-type binary sigma Ori AB is in the centre of the very young sigma Orionis cluster. I have computed the most probable distances and masses of the binary for several ages using a dynamical parallax-like method. It incorporates the BVRIH-band apparent magnitudes of both components, precise orbital parameters, interstellar extinction and a widely used grid of stellar models from the literature, Kepler's third law and a chi(2) minimization. The derived distance is 334(-22)(+25) pc for an age of 3 +/- 2 Ma; larger ages and distances are unlikely. The masses of the primary and the secondary lie on the approximate intervals 16-20 and 10-12 M-circle dot, respectively. I also discuss the possibility of sigma Ori AB being a triple system at similar to 385 pc. These results will help to constrain the properties of young stars and substellar objects in the sigma Orionis cluster.