The W UMa binaries USNO-A2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac: light curve solutions and global parameters based on the GAIA distances

TL;DR

This study analyzes four W UMa binary stars using photometric data and GAIA distances, revealing their overcontact nature, component characteristics, and orbital period variations, including a third body presence and a peculiar low-mass system.

Contribution

First detailed light curve solutions for these binaries incorporating GAIA distances, identifying a third body and peculiar low-mass overcontact system.

Findings

V471 Cas has a third body with 0.12 Msun.

V479 Lac shows a decreasing orbital period.

V560 Lac is a peculiar overcontact binary with total mass below 1 Msun.

Abstract

We present photometric observations in Sloan filters g', i' of the eclipsing W UMa stars USNO-A2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac. The sinusoidal-like O-C diagram of V471 Cas shows presence of third body with mass of 0.12 Msun (red dwarf) at distance 897 Rsun. The O-C diagram of V479 Lac reveals period decreasing. The results of the light curve solutions are: (i) The targets are overcontact binaries with small fill-out factors; (ii) Their components are F-K stars, comparable in size, whose temperature differences are below 80 K; (iii) All targets undergo partial eclipses and to limit the possible mass ratios we carried out two-step $q$-search analysis. The target global parameters (luminosities, radii, masses) were obtained on the base of their GAIA distances and the results of our light curve solutions. The obtained total mass of V560 Lac turns out smaller than the lower mass limit for the presently existing W UMa binaries of 1.0-1.2 Msun, i.e. this target is an peculiar overcontact system.