Astron. Astrophys. 345, 531-546 (1999)

Astron. Astrophys. 345, 531-546 (1999)

V606 Centauri: an early-type eclipsing contact binary ^*

Reinald Lorenz¹, Pavel Mayer² and Horst Drechsel¹

¹ Dr. Remeis-Sternwarte Bamberg, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstrasse 7, D-96049 Bamberg, Germany
² Astronomical Institute, Charles University, V Holeovikách 2, CZ-180 00 Praha 8, Czech Republic

Received 10 August 1998 / Accepted 9 December 1998

Abstract

We present a spectroscopic and photometric analysis of the early-type eclipsing binary V606 Cen. Based on new high-resolution CCD spectra the first radial velocity curve of this system is given, which allows for an accurate determination of radial velocity amplitudes ( [FORMULA] , ) and the spectroscopic mass ratio . Moreover, equivalent widths are listed. The line strengths of He I 4922 show strong variations with the orbital phase, related to the so-called (and hitherto unexplained) "Struve-Sahade effect". In this context, some aspects concerning the determination of equivalent widths in close binary systems are discussed, with special reference to the influence of the ellipsoidal light variations. For the first time, photoelectric UBV light curves of V606 Cen are presented, which were solved with the MORO code, based on the Wilson-Devinney model. The first set of solutions was achieved with effective temperatures according to the previous spectral classification B1-2 Ib/IIb, but the derived absolute dimensions, surface gravities, as well as an investigation of the equivalent widths led to a revision of the spectral type. We now suggest B0-0.5 V for the primary, and B2-3 V for the secondary component, respectively. Using the corresponding effective temperatures, another light curve analysis was performed, yielding the following absolute dimensions: [FORMULA] M, M, R, R, L, and L. In all cases, a contact configuration is found. The evolutionary state of V606 Cen is discussed in the light of modern evolutionary grids. It turns out that this contact system was formed during the slow phase of case A mass transfer after reversal of its mass ratio. In this respect it is similar to other early-type contact binaries such as V382 Cyg, V701 Sco or RZ Pyx.