2001MNRAS.327..435G

We present a detailed, extensive investigation of the photometric and spectroscopic behaviour of WR 30a. This star is definitely a binary system with a period around 4.6d. We propose the value P=4.619d (sigma=0.002d). The identification of the components as WO4+O5((f)) indicates a massive evolved binary system; the O5 component is a main-sequence or, more likely, a giant star. The radial velocities of the O star yield a circular orbit with an amplitude KO=29.9 (sigma=2.1)km.s^–1 and a mass function of 0.013 (sigma=0.003)M_solar. The spectrum of WR 30a exhibits strong profile variations of the broad emission lines that are phase-locked with the orbital period. We report the detection of the orbital motion of the WO component with K_WO=189km.s-1, but this should be confirmed by further observations. If correct, it implies a mass ratio M_WO/MO=0.16. The star exhibits sinusoidal light variations of amplitude 0.024mag peak-to-peak with the minimum of light occurring slightly after the conjunction with the O star in front. On the basis of the phase-locked profile variations of the Civ λ4658 blend in the spectrum of the WO, we conclude that a wind-wind collision phenomenon is present in the system. We discuss some possibilities for the geometry of the interaction region.