Improved Basic Physical Properties of the Oe-Star Binary V1007 Sco

Abstract

An analysis of new and published sets of spectroscopic and photometric observations of the astrophysically important eclipsing O+O binary system V1007 Sco in NGC 6231, leads to significantly improved basic physical properties of the system. We arrived at the following preliminary values for masses and radii: M ₁ = 28.4 M_⊙, M ₂ = 29.5 M_⊙, R ₁ = 15.6 R _⊙, R ₂ = 17.1 R_⊙. These values clearly indicate log g of about 3.5 [CGS], therefore the stars are Oe giants, not Of supergiants. Similarity to Be stars follows also from the fact that the Balmer and He I emission in the spectra from the year 2000 is much stronger than in the spectra taken several years ago. We also report the discovery of apsidal motion with a period of 132 years. Our solution implies a constant of internal structure essentially in agreement with its theoretical value and with the age of NGC 6231. We suggest that the masses, which still differ from the evolutionary ones, and the observed variable Balmer and He I emission may be related to the fact that both stars come very close to their respective limits of dynamical stability near periastron, and large mass loss from the system is likely.