A PHOTOMETRIC STUDY OF THE NEGLECTED ECLIPSING BINARY BS CASSIOPEIAE

Abstract

We present multicolor charge-coupled device (CCD) photometry for the eclipsing binary BS Cassiopeiae, observed on four nights between 2007 December and 2008 January. Using the Wilson -Devinney program, the photometric solution was derived from our BVR observations. Photometric results indicated that BS Cas is a W-subtype binary, whose mass ratio and overcontact degree are q = 0.2834(+/- 0.0010) and f = 31.6%(+/- 1.1%), respectively. Light curves of BS Cas present a typical O'Connell effect, which may be attributed to dark spot activity of the primary component. A detailed period analysis reveals that there exists a cyclic variation overlaying a secular period decrease, based on either all available light minimum times or recent light minimum times since 1989. The low-amplitude cyclic variation with a period of about 13 yr can be explained by either the light time effect or cyclic magnetic activity of both components. The long-term orbital period decrease suggests that BS Cas is undergoing mass transfer from the primary component to the secondary one. With its mass transfer and accompanying angular momentum loss, this binary will evolve into a deeper contact configuration.