Absolute parameters of young stars – II. V831 Centauri

Literature photometry and new high-resolution spectroscopy of V831 Cen are presented and analysed. Light and radial velocity curve fittings confirm the central pair of this young multiple system to be close to contact. Absolute parameters are found as follows: M1= 4.08 ± 0.07 M⊙, M2= 3.35 ± 0.06 M⊙, R1= 2.38 ± 0.03 R⊙, R2= 2.25 ± 0.03 R⊙, T1= 13 000 ± 300 K, T2= 11 800 ± 300 K; distance of 110 ± 10 pc and age of ∼20 ± 5 Myr. Detailed examination of the spectrograms indicates the third component (V831 Cen B) to be an Ap star. The orbit of the third star about the close binary is analysed using historic astrometric measurements. This allows an estimate of the third star's mass to be about 2.5 M⊙, but this is sensitive to the adopted distance and inclination values. It is, however, confirmed by the measured radial velocity of the third star. To some extent, such analysis can also be applied to the fourth star (V831 Cen C). The derived properties can be checked against the system's membership of the Scorpius–Centaurus OB2 association.