Photometric and Spectroscopic Studies for Two Magnetic-activity Contact Binaries: V724 And and QR Com

Abstract

We presented new CCD photometry for two contact binaries, V724 And and QR Com, which were observed during the 2020-2022 observing seasons. By using the W-D method, the photometric solutions were deduced from new observed data and TESS ones. Their asymmetric light curves were modeled by a dark spot on the more massive component. Results indicate that the starspot may immigrate or disappear on the surface of the active component. From the TESS observations of QR Com, it is discovered that the difference between light maxima exhibits a 29.5-d oscillation, which implies the continuous evolution of spot feathers on the time-scale of several weeks. Their mass ratio and fill-out factor are q = 2.308 and f = 11.55% for V724 And, and q = 0.624 and f = 12.77% for QR Com, respectively. From the (O − C) curve, the orbital period secularly decrease at a rate of dP/dt = −1.66 × 10^{−7} d yr^{−1} for V724 And and dP/dt = −3.98 × 10^{−7} d yr^{−1} for QR Com, which was interpreted by mass transfer from the less massive component to the more massive one. With mass transferring, this kind of shallow-contact binaries, V724 And and QR Com, will evolve into the broken-contact configurations.