Photometric and Spectroscopic study of Ten Low Mass Ratio Contact Binary Systems: Orbital Stability, O'Connell Effect and Infra-red Calcium Line Filling

TL;DR

This study analyzes ten low mass ratio contact binary systems, revealing their potential instability, magnetic activity through infrared Calcium line filling, and UV emissions, contributing to understanding their orbital stability and activity features.

Contribution

It provides detailed light curve modeling of ten low mass ratio contact binaries, identifying potential merger candidates and linking chromospheric activity with infrared Calcium line filling.

Findings

Three systems are potential merger candidates.

All systems show excess filling of infrared Calcium lines.

Systems exhibit UV excess indicating magnetic activity.

Abstract

Low mass ratio contact binary systems are more likely to have unstable orbits and potentially merge. In addition, such systems exhibit characteristics such as starspots and high energy emissions (UV) suggestive of chromospheric and magnetic activity. Light curve modelling of ten contact binary systems is reported. All were found to be of extreme low mass ratio ranging from 0.122 to 0.24 and three were found to be potentially unstable and possible merger candidates. Filling of the infrared Calcium absorption lines is a marker of increased chromospheric activity. We use the available LAMOST spectra along with matched standard spectra (broadened for rotation) to measure the excess filling of the central core depression flux of the two main infrared Calcium absorption lines at 8542 and 8662 angstroms. We find that all reported contact binaries have excess filling of the core flux in the infrared Calcium lines. Three of the systems reported were also observed by the GALEX mission and we find that all three have features of excess ultraviolet emissions further adding evidence for increased chromospheric activity in low mass ratio contact binaries. Analysis of both orbital stability and absorption line filling is dependent on the determination of geometric and absolute parameters from light curve modelling. Not an insignificant number of contact binary light curves exhibit the O'Connell effect, usually attributed to starspots. We discuss the inclusion of starspots in light curve solutions and how they influence the geometric and absolute parameters