Evidence of a Third Body and Photometric Solutions of a High Temperature Marginal Contact Binary CW Aqr

Abstract

Marginal contact binary systems are an important class of binary systems in exploited by astronomers to understand various astrophysical phenomena as they bridge both semi-detached and overcontact stages. We studied the photometric data of CW Aqr using the JCB 1.3 m telescope (JCBT), Kepler, and TESS to understand the period variations and constrain the light curve solutions. We noted that the period of CW Aqr is increasing with a mass transfer rate of = 7.53 × 10−8 M ⊙ yr−1 from the secondary to the primary component. We also ascertained cyclic deviations along with a parabolic trend in the O − C diagram. The residuals displayed a sinusoidal trend which was fitted with an LTTE, indicating the presence of a third body with an orbital period of P 3 ∼10 yr and e = 0.10. We fitted the JCBT, Kepler, and TESS photometric normalized light curves and noted the mass ratio to be q ∼ 0.32 for both contact and semi-detached configurations. We identified a temperature difference between the primary and secondary components of ∼2500 K. No activity signatures were found in the observed light curves which were also evident from the Hα line studies where the filled-in effect was not seen. Overall our study suggests that CW Aqr is a marginal contact binary with a low mass ratio evolving toward a semi-detached configuration. However, it may merge if the period increases due to ongoing mass transfer accompanied by a lowering in the mass ratio and later oscillate back to the period-decreasing trend due to angular momentum loss over a few cycles of thermal relaxation oscillations followed by instability.