2015AJ....150...70L

We present multi-color CCD photometry of the neglected contact binary XZ Leo. Completely covered VRI band light curves and four times of minimum light were obtained. Combining the photometric and previously published radial-velocity data, a revised photometric analysis was carried out for the binary system by applying the Wilson-Devinney code. With a hot spot placed on the massive primary component near the neck region of the common envelope, the light curves were satisfactorily modeled. The photometric solution combined with the radial-velocity solution reveals that XZ Leo is an A-type contact binary with a degree of contact of 24(±1)%. The absolute parameters of the components were determined to be M₁= 1.74(±0.06)M_☉, M₂= 0.61(±0.02)M_☉, R₁= 1.69(±0.01)R_☉, R₂= 1.07(±0.01)R_☉, L₁= 6.73(±0.08) L_☉, and L₂= 2.40(±0.04)L_☉. Based on all the available data, the long-term orbital period behavior of the system was investigated. It indicates that the binary system was undergoing a continuous orbital period increase in the past three decades with a rate of dP/dt = +6.12 x 10^–8 days/yr, which suggests a probable mass transfer from the secondary to the primary component at a rate of dM/dt = 3.92 x 10^{–8^M}☉_/yr. The binary system is expected to evolve into the broken-contact stage in 1.56 x 10⁶ years. This could be evidence supporting the thermal relaxation oscillation theory.