BSN: Photometric Light Curve Analysis of Two Contact Binary Systems LS Del and V997 Cyg

The light curve analyses and orbital period variations for two W Ursae Majoris (W UMa) binary stars, LS Del and V997 Cyg, were presented in this work which was conducted in the frame of the Binary Systems of South and North (BSN) Project. Ground-based photometric observations were performed at two observatories in France. We used TESS (The Transiting Exoplanet Survey Satellite) data for extracting times of minima and light curve analysis of the target systems. The O-C diagram for both systems displays a parabolic trend. LS Del and V997 Cyg's orbital periods are increasing at a rate of $dP/dt= 7.20\times10^{-08}$ $d\ yr^{-1}$ and $dP/dt= 2.54\times10^{-08}$ $d\ yr^{-1}$, respectively. Therefore, it can be concluded that the mass is being transferred from the less massive star to the more massive component with a rate of $dM/dt=-1.96\times10^{-7}$ $M_\odot$ $yr^{-1}$ for LS Del system, and $dM/dt=-3.83\times10^{-7}$ $M_\odot$ $yr^{-1}$ for V997 Cyg. The parameters of the third possible object in the system were also considered. The PHysics Of Eclipsing BinariEs (PHOEBE) Python code was used to analyze the light curves. The light curve solutions needed a cold starspot due to the asymmetry in the LS Del system's light curve maxima. The mass ratio, fill-out factor, and star temperature all indicate that both systems are contact binary types in this investigation. Two methods were used to estimate the absolute parameters of the systems: one method used the parallax of Gaia Data Release 3 (EDR3), and the other used a $P-M$ relationship. The positions of the systems were also depicted on the $M-L$, $M-R$, $q-L_{ratio}$, and $logM_{tot}-logJ_0$ diagrams.