APSIDAL MOTION AND REVISED PHOTOMETRIC ELEMENTS OF THE ECCENTRIC ECLIPSING BINARY V-477 CYGNI

Accurate physical parameters have been determined for the component stars of the eclipsing binary V 477 Cygni (Sp. A3 V, V = 8.3, P = 2.35 d). This is a very little evolved system with an eccentric orbit which clearly shows apsidal motion effects, not only in the changing position of the eclipses, but also in the photometric light curve. A rediscussion of the photometric data of O'Connell (1970) using an extended version of the synthetic light curve computer code EBOP, which takes into account variable position of the periastron, has been carried out. The obtained results, combined with existing radial velocity curves by Popper (1968), lead to absolute radii of 1.57 +/- 0.05 (star A) and 1.27 +/- 0.04 (star B) and masses of 1.79 +/- 0.12 M. and 1.35 +/- 0.07 M.. This places V 477 Cygni in a very interesting region of the HR diagram close to the ZAMS where theoretical models predict a turn point in the log g-log T(eff) plane. The larger and more massive star is also the hotter one and effective temperatures have been estimated from colour indices to be 8700, 6700 K for each of the components. The orbit of V 477 Cygni is highly eccentric (e = 0.307) and an apsidal motion rate with a period of 350 +/- 10 yr has been found. Absolute dimensions have been compared to available theoretical models using both, standard physics (Claret & Gimenez 1989) and a moderate amount of convective overshooting (Claret & Gimenez 1991). A satisfactory fit is provided in the two cases due to the small differences expected for such unevolved stars and an age log t = 8.4 +/- 0.3 yr could be estimated from the location of the primary component. Models with solar initial chemical composition have been adopted throughout. The internal structure constant derived from the observed apsidal motion rate (log k2 = -2.20 +/- 0.04) indicates, for the first time, a slightly less centrally-concentrated configuration than predicted by theoretical models.