The first CCD photometric study of the neglected W UMa-type binary PP Lacertae

The first complete charge couple device (CCD) photometric light curve in V band of the neglected W UMa-type binary star, PP Lacertae, is presented. It is shown that the system is a complete eclipsing binary and belongs to W type according to Binnendijk's classification where the occultation minimum is much deep than the transit one. The light curve is symmetric and no day-to-day variation of the light curve was found. These properties enable good chance to determine photometric parameters of the binary system. Photometric solutions based on the complete light curve were derived with the 2003 version of the W-D code. It is suggested that PP Lacertae is a W-type overcontact binary system with a mass ratio of q = 2.3000(±0.0044) and a median degree of overcontact of f = 23.9%(±1.1%). The temperature of the less massive component is about 260 K higher than that of the more massive one. Our four CCD times of light minimum, including others collected from the literature, have been used for the period study. It is found that the period showed a small-amplitude cyclic oscillation with a period of 19.7 years and an amplitude of 0.d0058, which can be explained as the light-time effect of an unseen third body.