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

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 $M_2$ = 0.73 $M_{\odot }$, $R_1$ = 1.39 $R_{\odot }$ and $R_2$ = 1.09 $R_{\odot }$ for BK Vul, and $M_2$ = 0.36 $M_{\odot }$, $R_1$ = 2.40 $R_{\odot }$ and $R_2$ = 1.33 $R_{\odot }$ 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 $\times 10^{-7}$ day yr⁻¹ and 27 yrs., respectively. The evolutionary status of components of both systems were discussed.