2023RAA....23e5009V

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 $\dot{m}$ = 7.53 × 10^–8M_⊙ 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 P₃ ∼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.