The Varying Light Curve and Timings of the Ultra-short Period Contact Binary KIC 9532219

TL;DR

This study analyzes the light curve variations and timing behavior of the ultra-short period contact binary KIC 9532219, revealing effects of third-body interactions, starspot activity, and contamination from a nearby star.

Contribution

It provides a detailed analysis of the light curve and period variations, identifying the influence of a third body and starspots on the system's observed properties.

Findings

Eclipsing pair is in a marginal contact stage with a mass ratio of 1.20.

Period variations are due to a third body with a 1196-day orbit.

Light-curve changes are mainly caused by contamination and starspot activity.

Abstract

KIC 9532219 is a W UMa-type eclipsing binary with an orbital period of 0.1981549 d that is below the short-period limit ($\sim$0.22 d) of the period distribution for contact binaries. The {\it Kepler} light curve of the system exhibits striking light changes in both eclipse depths and light maxima. Applying third-body and spot effects, the light-curve synthesis indicates that the eclipsing pair is currently in a marginal contact stage with a mass ratio of $q$=1.20, an orbital inclination of $i$=66.0 deg, a temperature difference of $\Delta$ ($T_{1}$--$T_{2}$)=172 K, and a third light of $l_3$=75.9 \%. To understand the light variations with time, we divided up the light curve into 312 segments and separately analyzed them. The results reveal that variation of eclipse depth is primarily caused by changing amounts of contamination due to the nearby star KIC9532228 between the {\it Kepler} Quarters and that the variable O'Connell effect originates from the starspot activity on the less massive primary component. Based on our light-curve timings, a period study of KIC 9532219 indicates that the orbital period has varied as a combination of a downward parabola and a light-travel-time (LTT) effect due to a third body, with a period of 1196 d and a minimum mass of 0.0892 $M_\odot$ in an eccentric orbit of 0.150. The parabolic variation could be a small part of a second LTT orbit due to a fourth component in a wider orbit, instead of either mass transfer or angular momentum loss.