Period changes and four-color light curves of the active overcontact binary v396 monocerotis

Abstract

This paper analyzes the first secured four color light curves of V396 Mon using the 2003 version of the WD code. It is confirmed that V396 Mon is a shallow W-type contact binary system with a mass ratio $q=2.554(\pm0.004)$ and a degree of contact factor $f=18.9%(\pm1.2%)$. A period investigation based on all available data shows that the period of the system includes a long-term decrease ($dP/dt=-8.57\times{10^{-8}}$ days/year) and an oscillation ($A_3=0.^{d}0160$; $T_3=42.4\,years$). They are caused by angular momentum loss (AML) and light-time effect, respectively. The suspect third body perhaps is a small M-type star (about 0.31 solar mass). Though some proofs show that this system has strong magnetic activity, through analyzing we found that the Applegate mechanism cannot explain the periodic changes. This binary is an especially important system according to Qian's statistics of contact binaries as its mass ratio lies near the proposed pivot point about which the physical structure of contact binaries supposedly oscillate.