Photometric investigation on the W-subtype contact binary V1197 Her

Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at Thai National Observatory and the Wilson-Devinney (W-D) program is 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 fill-out factor to be $f = 15.7,%$. The temperature difference between the primary star and secondary star is only $140K$ in spite of the low degree of contact, which means that V1197 Her is not only in geometrical contact configuration but also already under thermal contact status. The orbital inclination of V1197 Her is as high as $i = 82.7^{circ}$, 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 $M_{1} = 0.30(1)M_odot$, $M_{2} = 0.77(2)M_odot$, $R_{1} = 0.54(1)R_odot$, $R_{2} = 0.83(1)R_odot$, $L_{1} = 0.18(1)L_odot$ and $L_{2} = 0.38(1)L_odot$. The evolutionary status of the two component stars are drawn in the H - R diagram, which shows 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 $dP/dt=-2.58times{10^{-7}}daycdot year^{-1}$, which can be explained by mass transfer from the more massive star to the less massive one with a rate of $frac{dM_{2}}{dt}=- 1.61times{10^{-7}}M_odot/year$. The light curves of V1197 Her is reported to have the OConnell effect. Thus, a cool spot is added to the massive star to model the asymmetry on light curves.