Periodic Variation Studies of the Two Short Period W UMa-type Eclipsing Binaries: LX Lyn and V0853 Aur

In this paper, new light curves (LCs) of contact eclipsing binary (CEB) systems LX Lyn and V0853 Aur are presented and analysed by using the 2015 version of the Wilson-Devinney (W-D) code. In order to explain the asymmetric LCs of them, cool star-spots on the components were employed. It is suggested that the fill-out degree of them are f=12.0\% (LX Lyn) and f=26.3\% (V0853 Aur), respectively. At the same time, we found that LX Lyn is a W-type eclipsing binary (EB) with an orbital inclination of $i=84.88^{\circ}$ and a mass ratio of $q=2.31$. V0853 Aur is also a W-type CEB with a mass ratio of $q=2.77$ and an orbital inclination of $i$=$79.26^{\circ}$. Based on all available times of light minimum, the orbital period changes of them are studied by using the $O-C$ method. The $O-C$ diagram of LX Lyn reveals a cyclic oscillation with a period about 14.84 years and an amplitude of 0.0019 days, which can be explained by the light-travel time effect (LTTE) due to the presence of a third body with a minimum mass of 0.06$M_\odot$. For V0853 Aur, it is discovered that the $O-C$ diagram of the system also shows a cyclic oscillation with a period of 9.64 years and an amplitude of 0.03365 days. The cyclic oscillation of V0853 Aur can be attributed to the LTTE by means of a third body with a mass no less than 3.77$M_\odot$. The third body may play an important role in the formation and evolution of these systems.