The Kepler Eclipsing Binary V2281 Cygni with Twin Stars

Abstract

We present the physical properties of the eclipsing binary V2281 Cyg, which shows a light-time effect due to a supposed tertiary component from its eclipse timing variation according to the Kepler observations. The high-resolution spectra and BVR photometric data of the system were obtained at Bohyunsan Optical Astronomy Observatory and Mount Lemmon Optical Astronomy Observatory, respectively. To determine the fundamental parameters of the eclipsing pair and its circumbinary object, we simultaneously analyzed the radial velocities, light curves, and eclipse times including the Kepler data. The masses and radii for the primary and secondary stars were determined with accuracy levels of approximately 2% and 1%, respectively, as follows: M₁=1.61± 0.04 M_⊙ and M₂ =1.60± 0.04 M_⊙, R₁=1.94± 0.02 R_⊙ and R₂=1.93± 0.02 R_⊙. If its orbit is coplanar with the eclipsing binary, the period and semimajor axis of the third body were calculated to be P_3b=4.1 years and a_3b=4.06 au, respectively, and its mass is M_3b=0.75 M_⊙. The evolutionary state of the system was investigated by comparing the masses and radii with theoretical models. The results demonstrate that V2281 Cyg is a detached eclipsing binary, which consists of twin main-sequence stars with an age of 1.5 Gyr.