Photometric investigation on the W-subtype contact binary V1197 Her

Abstract

Abstract Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at the Thai National Observatory and the Wilson-Devinney (W-D) program was used to model the observational light curves. The photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of q = 2.61 and a fill-out factor of f = 15.7%. The temperature difference between the primary star and secondary star is only 140 K in spite of the low degree of contact, which means that V1197 Her is not only in geometrical contact configuration but is also already under thermal contact status. The orbital inclination of V1197 Her is as high as i = 82.7°, and the primary star is completely eclipsed at the primary minimum. The totally eclipsing characteristic implies that the determined physical parameters are highly reliable. The masses, radii and luminosities of the primary star (star 1) and secondary star (star 2) are estimated to be M 1 = 0.30(1) M ⊙, M 2 = 0.77(2) M ⊙, R 1 = 0.54(1) R ⊙, R 2 = 0.83(1) R ⊙, L 1 = 0.18(1) L ⊙ and L 2 = 0.38(1) L ⊙. The evolutionary statuses of the two component stars are drawn in the Hertzsprung-Russell diagram, showing that the less massive but hotter primary star is more evolved than the secondary star. The period of V1197 Her is decreasing continuously at a rate of dP/dt = −2.58 × 10−7 day · year−1, which can be explained by mass transfer from the more massive star to the less massive one at a rate of d M 2 d t = − 1.61 × 10 − 7 M ⊙ year−1. The light curves of V1197 Her are reported to show the O'Connell effect. Thus, a cool spot is added to the more massive star to model the asymmetry in the light curves.