Orbital Period Changes of Selected Two Semi-Detached Binaries

Abstract

Since the data obtained from satellite data are very sensitive, the minima times of the target systems have obtained from Kepler (K2) and TESS observations. A total of 14 minima times were obtained from Kepler (K2) data for the AF Gem system and 11 minima times in two different sectors from the TESS data for the RY Gem system. In this study, orbital period behaviours of semi-detached binaries (SDBs) AF Gem and RY Gem systems have investigated, together with minima times obtained from literature and satellite data. It has been observed that the orbital periods of AF Gem and RY Gem decrease. The period change rates of AF Gem and RY Gem systems are determined as dP/dt = -4.1×10-8 and dP/dt = -6.5×10-6 day/yr. The magnetic activity of the systems' cooler components may be the cause of the periods' decrease, and so the mass loss rates of the systems have been estimated. For AF Gem and RY Gem, mass loss rate was found to be -4.4×10-8 M⊙/yr and -8.2×10-7 M⊙/yr, respectively. In the O-C graph of AF Gem, sinusoidal changes also exist. A tertiary body around the eclipsing pair can be used to depict a sinusoidal variation caused by a light time effect (LITE). The minimum mass of a possible third star in the vicinity of AF Gem has been determined to be 0.24 M⊙.