Long-term photometric study of a faint W UMa binary in the direction of M31

TL;DR

This study re-analyzed photometric data of a faint W UMa binary near M31, determining its orbital and physical parameters, and classified it as a low mass-ratio over-contact binary of A-subtype at about 2.64 kpc.

Contribution

It provides detailed photometric analysis and physical characterization of a faint W UMa binary in the M31 direction, using archival data and empirical relations.

Findings

Orbital period of 0.2664 days identified.

Binary classified as low mass-ratio over-contact A-subtype.

Located approximately 2.64 kpc away with high fill-out factor.

Abstract

We carry out a re-analysis of the photometric data in Cousin RI bands which was taken under the Nainital Microlensing Survey during 1998 to 2002 with the aim to detect gravitational microlensing events in the direction of M31. Here, we do photometric analysis of a faint W UMa binary CSS_J004259.3+410629 identified in the target field. The orbital period of this star is found to be 0.266402+/-0.000018 day. The photometric mass ratio, q, is found to be 0.28+/-0.01. The photometric light curves are investigated using the Wilson-Devinney code and absolute parameters are determined using empirical relations which provide masses and radii of the binary as M1 = 1.19+/-0.09 Msun, M2 = 0.33+/-0.02 Msun and R1 = 1.02+/-0.04 Rsun, R2 = 0.58+/-0.08 Rsun based on the Rc band data. Almost similar values are found by analysing Ic band data. From the photometric light curve examination, the star is understood to be a low mass-ratio over-contact binary of A-subtype with a high fill-out factor of about 47%. The binary system is found to be located approximately at a distance of 2.64+/-0.03 kpc having a separation of 2.01+/-0.05 Rsun between the two components.