The lightcurve intrinsic variability in 47 Kepler contact binary stars

TL;DR

This study investigates how intrinsic variability affects the modeling of contact binary star light curves, revealing a cutoff at 0.45 days and implications for physical parameter estimation and classification.

Contribution

It introduces a new approach to analyze intrinsic variability in contact binaries and proposes a cutoff period for variability effects based on Kepler data.

Findings

Intrinsic variability increases apparent mass ratio by 5%.

A sharp cutoff of variability at P=0.45 days was identified.

Over half of the binaries may have third companions.

Abstract

This work studies the significance of the lightcurve intrinsic variability in the numerical modeling of contact binaries. Using synthetic light curves we are showing that the starspot-based intrinsic variability increases the apparent mass ratio by $\Delta q=5$%. For systems with orbital period $P>0.3 d$ the effect of intrinsic variability averaged over long time cancels each other out with the Kepler Mission-like phase smearing. Further, we analyse 47 totally eclipsing Kepler Mission contact binaries. We found a sharp cutoff of the intrinsic variability at P = 0.45 d. With the light curve numerical modeling and observational relations we derive physical parameters of the 47 systems. At least 53% of binaries have a possible third companion. 21 binaries show the O`Connell effect in the averaged phase curve. 19 of them have a primary maximum lower than the secondary, suggesting a stationary dark region on the trailing side. Using the P = 0.45 d cutoff we propose a new approach on the Period-Color relation. The only parameter correlating with the magnitude of the intrinsic variability is the apparent effective temperature ratio. We conclude that instead of describing the system parameters, the A/W-subtype division should be applicable only to the lightcurves, as a tentative phenomenon.