Spectroscopic and photometric study for five late G- to K-type short-period contact binaries

Abstract

We reported spectroscopy and photometry for five ultra-short period W UMa-type contact binaries. Eleven sets of low resolution spectra are obtained from the Large Sky Area Multiobject Fiber Spectroscopic Telescope (LAMOST) database and analyzed. It has been determined that these systems are late G- to K-type stars: G7V for J0658, G9V for LINEAR 3562115, K0V for PS Com, and K5V for LINEAR 11570575. Additionally, it was observed that the cooler the star, the stronger the sodium absorption line. Seven sets of complete light curves, including two sets of TESS data for PS Com and V0568 Peg, were analyzed using the W-D code. All the five targets are W-subtype systems with mass ratios ($q$) greater than 1. The light curves of the two medium contact systems (J0658 and LINEAR 11570575) are symmetric. In contrast, the light curves of the three shallow contact binaries (LINEAR 3562115, PS Com, and V0568 Peg) show differences between their two maxima, Max.I and Max.II, suggesting the presence of cool or hot spots on their surfaces. According to the H-R diagram, the more massive components of these targets are situated between the ZAMS and TAMS, while the less massive ones are overheated due to energy transfer within the common envelope. As these binaries lose angular momentum, they will evolve into deep, low mass ratio contact binaries.