A Single-lined Spectroscopic Binary Companion to an Active and Deep Contact Binary in a Quintuple Stellar System

Abstract

Abstract V410 Aur is a known deep and low-mass-ratio contact binary with a spectroscopically tertiary component and a visual companion. However, the physical and orbital properties of the tertiary are unknown. We constructed (O − C) curve with 117 new eclipse times and those collected from the literature, which shows a cyclical variation with a period of 25.44 (±1.17) yr and a projected semimajor axis of 0.0348 (±0.0021) days while it undergoes a long-term period decrease at a rate of dP/dt = −1.58 × 10−7daysyr−1. The cyclical variation is analyzed for the light-travel time effect. The minimum mass of the third body is determined as 1.39 (±0.13) M ⊙ that is much larger than the inferred value (0.97 M ⊙) of spectroscopic investigation, which indicates that the spectroscopically tertiary is a single-lined spectroscopic binary with an unseen component. The maximum orbital semimajor axis 6.19 (±0.67) au of the third body is determined. Gaia detected a visual companion to V410 Aur at practically the same distance from the Sun nicely confirming the physical bond. These results reveal that V410 Aur contains a single-lined spectroscopic binary with a visual companion in a quintuple stellar system. TESS photometric solutions confirmed that V410 Aur is a deep overcontact binary with a fill-out factor of 73.83(88)% where the additional light contribution is about 24.80(18)%. The continuous variations of light curves are explained by the evolution of a dark spot on the more massive component. The parabolic variation in the (O − C) curve may be caused by the mass transfer from the massive component to the less massive one in the deep overcontact binary.