Photometric Investigation and Possible Light-Time Effect in the Orbital Period of a Marginal Contact System, CW Cassiopeiae

Abstract

Abstract The first complete charge-coupled device (CCD) light curves in $B$ and $V$ passbands of a neglected contact binary system, CW Cassiopeiae (CW Cas), are presented. They were analyzed simultaneously by using the Wilson and Devinney (WD) code (1971, ApJ, 166, 605). The photometric solution indicates that CW Cas is a W-type W UMa system with a mass ratio of $m_{2}/m_{1} =$ 2.234, and that it is in a marginal contact state with a contact degree of $\sim$ 6.5% and a relatively large temperature difference of $\sim$ 327 K between its two components. Based on the minimum times collected from the literature, together with the new ones obtained in this study, the orbital period changes of CW Cas were investigated in detail. It was found that a periodical variation overlaps with a secular period decrease in its orbital period. The long-term period decrease with a rate of $dP/dt = -$3.44 $\times$ 10$^{-8} $d yr$^{-1}$ can be interpreted either by mass transfer from the more-massive component to the less-massive with a rate of ${d}m_{2}/dt = -$3.6 $\times$ 10$^{-8} M_{\odot} $yr$^{-1}$, or by mass and angular-momentum losses through magnetic braking due to a magnetic stellar wind. A low-amplitude cyclic variation with a period of $T =$ 63.7 yr might be caused by the light-time effect due to the presence of a third body.