A Turnoff Detached Binary Star V568 Lyr in the Kepler Field of the Oldest Open Cluster (NGC 6791) in the Galaxy

TL;DR

This study analyzes the detached binary star V568 Lyr in the old, metal-rich open cluster NGC 6791 using Kepler data, deriving stellar parameters, cluster distance, and testing stellar evolution models.

Contribution

It provides precise stellar parameters for V568 Lyr and compares observations with evolution models to explore binary star evolution in a high-metallicity environment.

Findings

Stellar masses, radii, and luminosities are precisely determined.

The cluster distance is estimated at 4.26 kpc.

Evolution models fit the data with metallicity Z=0.04 and age 7.7 Gyr.

Abstract

We present the Kepler photometric light-variation analysis of the late-type double-lined binary system V568 Lyr that is in the field of the high metallicity old open cluster NGC 6791. The radial velocity and the high-quality short-cadence light curve of the system are analysed simultaneously. The masses, radii and luminosities of the component stars are $M_1 = 1.0886\pm0.0031\, M{\odot}$, $M_2 = 0.8292 \pm 0.0026\, M{\odot}$, $R_1 = 1.4203\pm 0.0058\, R{\odot}$, $R_2 = 0.7997 \pm 0.0015\, R{\odot}$, $L_1 = 1.85\pm 0.15\, L{\odot}$, $L_2 = 0.292 \pm 0.018\, L{\odot}$ and their separation is $a = 31.060 \pm 0.002\, R{\odot}$. The distance to NGC 6791 is determined to be $4.260\pm 0.290\,$kpc by analysis of this binary system. We fit the components of this well-detached binary system with evolution models made with the Cambridge STARS and TWIN codes to test low-mass binary star evolution. We find a good fit with a metallicity of $Z = 0.04$ and an age of $7.704\,$Gyr. The standard tidal dissipation, included in TWIN is insufficient to arrive at the observed circular orbit unless it formed rather circular to begin with.