The Kepler Eclipsing Binary V2281 Cygni with Twin Stars

TL;DR

This study characterizes the physical properties of the eclipsing binary V2281 Cyg, revealing twin main-sequence stars with a tertiary component, using combined spectroscopic, photometric, and eclipse timing data from Kepler and ground observatories.

Contribution

First simultaneous analysis of radial velocities, light curves, and eclipse timings of V2281 Cyg, including a tertiary component, to determine precise stellar and orbital parameters.

Findings

Masses and radii determined with 1-2% accuracy.

Detected a tertiary component with a 4.1-year orbit and 0.75 solar masses.

System is a detached binary of twin main-sequence stars, 1.5 Gyr old.

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: $M_{1} = 1.61 \pm 0.04$ M$_\odot$ and $M_{2} = 1.60 \pm 0.04$ M$_\odot$, $R_{1} = 1.94 \pm 0.02$ R$_\odot$ and $R_{2} = 1.93 \pm 0.02$ R$_\odot$. 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$_\odot$. 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.