A variable star population in the open cluster NGC\,6819 observed by the Kepler spacecraft

TL;DR

This study identifies and classifies 385 variable stars in the open cluster NGC 6819 using Kepler data, confirming cluster parameters and analyzing orbital period variations among binaries.

Contribution

It provides a comprehensive catalog of variable stars in NGC 6819 with cluster membership, orbital parameters, and period variation analysis, expanding previous work with Gaia data integration.

Findings

128 variable stars are confirmed as cluster members.

Only five objects show significant orbital period variation.

Derived cluster parameters: age 2.54 Gyr, distance 2.3 kpc, [Fe/H] = -0.01.

Abstract

We present the list of variable stars we found in the \kep\ superstamp data covering approximately nine arcminutes from the central region of NGC6819. This is a continuation of our work presented by Sanjayan et al.(2022a). We classified the variable stars based on the variability type and we established their cluster membership based on the available Gaia Data Release 3 astrometry. Our search revealed 385 variable stars but only 128 were found to be cluster members. In the case of eclipsing and contact binaries we calculated the mid-times of eclipses and derived ephemerides. We searched for eclipse timing variation using the observed minus calculated diagrams. Only five objects show significant orbital period variation. We used isochrones calculated within the MESA Isochrones and Stellar Tracks project and derived the average age (2.54 Gyr), average distance (2.3 kpc) and iron content [Fe/H] = -0.01(2), of NGC6819. We confirm this distance by the one derived from Gaia astrometry of the cluster members with membership probabilities greater than 0.9.