Photometric studies for two contact binaries: V532 Monocerotis and GU Orionis

Abstract

Abstract We present photometry and spectroscopy data for V532 Mon and GU Ori, observed in 2011 and 2016. From the spectral observations, the spectral types are determined to be F5V for V532 Mon and G0V for GU Ori. With the 2015-version Wilson–Devinney program, the photometric solutions are simultaneously deduced from VR light curves (LCs). The intrinsic variability for V532 Mon is found by comparing LCs in 2004 and 2011, while the asymmetric LCs for GU Ori are modeled by a cool spot on the more massive component. The results imply that the two stars are A-type contact binaries. The mass ratios and fill-out factors are, respectively, q = 0.190(±0.006) and f = 43.7(±0.9)% for V532 Mon and q = 0.455(±0.020) and f = 26.9(±1.3)% for GU Ori. From the (O − C) curves, it is found that their orbital periods may be undergoing long-term variations. The rates of period change are dP/dt = −1.72(±0.05) × 10−7 d yr−1 for V532 Mon and dP/dt = +1.45(±0.01) × 10−7 d yr−1 for GU Ori. V532 Mon with a decreasing period will evolve into a deep-contact binary, while GU Ori with an increasing period may evolve into a broken-contact case.