Orbital solution and fundamental parameters of σ Scorpii

Abstract

The first orbital solution for the spectroscopic pair in the multiple star system σ Scorpii, determined from measurements with the Sydney University Stellar Interferometer, is presented. The primary component is of β Cephei variable type and has been one of the most intensively studied examples of its class. The orbital solution, when combined with radial velocity results found in the literature, yields a distance of 174⁺²³_-18pc, which is consistent with, but more accurate than the Hipparcos value. For the primary component we determine 18.4 +/- 5.4M_solar, -4.12 +/- 0.34 mag and 12.7 +/- 1.8R_solar for the mass, absolute visual magnitude and radius, respectively. A B1 dwarf spectral type and luminosity class for the secondary is proposed from the mass determination of 11.9 +/- 3.1M_solar and the estimated system age of 10Myr.