Photometry, light curve solution and period study of contact binary BX And

The photometry of the binary star BX And (HIP 10027) is performed during several nights in October and November 2019, and October 2020 using B, V, and R Johnson-Cousins filters in Dr. Mojtahedi Observatory of the University of Birjand. Astronomical image processing and data reduction are performed by the IRIS software and light curves are obtained. These curves, along with the radial velocity data of the binary star, are analyzed by the Phoebe program to determine the physical and geometric parameters of the system. The evolutionary state of this system is investigated using the Hertzsprung-Russell (H-R) and density vs color index diagrams. The O-C curve is plotted using the eclipse times obtained in this study and those reported in the literature. By fitting a quadratic function to this curve, a new linear ephemeris is obtained for the system, and the mass transfer rate between the components of the system is determined. A periodic behavior is observed in the residuals, after subtracting the quadratic function from the O-C curve. These periodic changes are attributed to the presence of a third component in the system. The parameters of the third component are determined by fitting the light-time function to the residuals curve.