Photometric analysis of the contact binary star V842 Hercules on the basis of seasonal light curves

We present new BVR light curves and photometric analysis of the contact binary star V842 Her. The light curves were obtained at the ÇOMU Observatory in the consecutive years 2003, 2004, 2005, and also 2007. We studied the variation of the orbital period of the system. The O–C diagram shows a quasi-sinusoidal form superimposed on a parabola. The parabolic variation, which indicates the secular increase of the orbital period of the system, was interpreted in terms of the combined effect of mass transfer between the components of the system and mass loss by a stellar wind from the system. The sinusoidal form of the orbital period variation was considered as an apparent change and interpreted in term of the light-time effect due to an unseen component in the system. We have also studied the nature of asymmetries and the intrinsic variability in the light curves of the system. The differences between light levels of both maxima (i.e. O’Connell effect) and minima are changing with time. These peculiar asymmetries were explained by a dark spot on the surface of the large and more massive component star. The present BVR   light curves and radial velocity curves obtained by [Rucinski, S.M., Lu, W., 1999. AJ 118, 2451] were analysed by means of the Wilson–Devinney method supplemented with a Monte Carlo type algorithm. Absolute parameters of the system were also derived. They are m1m1 = 0.38 m⊙m⊙, m2m2 = 1.45 m⊙m⊙, R1R1 = 0.81 R⊙R⊙, R2R2 = 1.47 R⊙R⊙, MV,1MV,1 = 5m5m.08 and MV,2MV,2 = 4m4m.06.