Physical parameters of the Algol system VW Hydrae from simultaneous analysis of G eneva seven-colour light curves

Abstract

The semi-detached eclipsing binary system VW Hydrae ( P = 2.70 days) has been analysed using the Wilson–Devinney program, on the basis of light curves obtained in the G eneva seven-colour photometric system, and radial velocity curves for both components measured with the cross-correlation technique. The physical and orbital parameters have been determined through a self-consistent simultaneous solution of light curves in seven colours and of the radial velocity curves of both components. The effective temperature of the primary component is determined from the photometric analysis, T eff 1 = 10 , 650 ± 200 K . It is shown that this value can be very well determined, despite the fact the primary eclipse is partial, by the use of colour indexes, as e.g. [ B 2 − V 1] 0. The absolute elements of the components are for the primary (mass gainer), with the value of T eff 1 fixed, M 1 = 3.10 ± 0.07 M ⊙, R 1 = 2.60 ± 0.01 R ⊙, M bol 1 = 0.05 ± 0.01 , and for the secondary (mass loser), M 2 = 0.76 ± 0.02 M ⊙, R 2 = 3.38 ± 0.01 R ⊙, M bol 2 = 2.90 ± 0.01 , T eff 2 = 4848 ± 6 K . The semi-major axis A of the relative orbit is 12.771 ± 0.090 R ⊙. The estimated spectral types of the components are about B8/9 V (primary) and F9 III. The equatorial rotational velocity of the primary (54 km s −1) shows that the system is synchronised. The distance to VW Hya is evaluated to 1122 ± 42 pc, and the colour excess E[ B 2 − V 1] to 0.046 ± 0.022.