First photometric study of W UMa-type binary systems: BK Vul and V699 Cep

Abstract

In this study, new CCD photometric observations and photometric analysis of BK Vul and V699 Cep systems, which are classified as contact binaries in the literature, are presented. For the V699 Cep, the TESS light curve was also used in the photometric analysis. We determined the basic astrophysical parameters of the BK Vul and V699 Cep systems from photometric analysis using the Wilson–Devinney method. Due to the lack of spectroscopic data for both systems in the literature, these absolute parameters were approximately calculated as to be M2 = 0.73 M⊙, R1 = 1.39 R⊙ and R2 = 1.09 R⊙ for BK Vul, and M2 = 0.36 M⊙, R1 = 2.40 R⊙ and R2 = 1.33 R⊙ for V699 Cep after estimating the mass of the primary component. The period decrease rate (dP/dt) and cyclic variation period of BK Vul were determined from the O−C analysis as -3.86 ×10−7 day yr−1 and 27 yrs., respectively. The evolutionary status of components of both systems were discussed.