An astrometric and photometric study of the intermediate-age open cluster ngc 2158 and its eclipsing binary [nbn2015j78

Abstract

We present a photometric and ast.rometric analysis of the NGC 2158 cluster using Gaia DR2 and 2MASS data. The cluster age, color excess, intrinsic distance modulus and distance are calculated to be t = 2.240 ± 0.260 Gvr, E(B-V) = 0.420 ±0.050 mag, (m-M)0 = 12.540 ±0.130 mag and dQ = 3224 ± 200 pc respectively. The photometric analysis and light curve modelling of the proposed eclipsing binary member [NBN2015]78 is performed using the latest version of the Wilson-Devinney (W-D) code. The solutions show that the system is an over-contact binary with a secondary component filling its Roche lobe, with a mass ratio q = 0.262. The primary and the secondary components of the system consist of two late spectral types Kl and K2 respectively. The membership of [NBN2015]78 is discussed using two independent methods, and we find that [NBN2015]78 is an interloper and not a member of NGC 2158.