White-Light Flares on Close Binaries Observed with Kepler

TL;DR

This study analyzes white-light flares on 1049 close binaries using Kepler data, revealing how flare activity varies with binary morphology, orbital, and rotation periods, and examining phase-dependent flare rates.

Contribution

It provides the first comprehensive analysis of flare activity across different binary types and orbital parameters using Kepler data, highlighting new correlations and phase behaviors.

Findings

Flare binary fraction is 10-20% lower in over-contact and ellipsoidal binaries.

Flare activity level increases with decreasing orbital and rotation periods up to a critical point, then decreases.

No correlation between flaring rate and orbital phase in eclipsing binaries, but bimodal distribution in non-eclipsing ellipsoidal binaries.

Abstract

Based on Kepler data, we present the results of a search for white-light flares on 1049 close binaries. We identify 234 flare binaries, on which 6818 flares are detected. We compare the flare-binary fraction in different binary morphologies ("detachedness"). The result shows that the fractions in over-contact and ellipsoidal binaries are approximately 10-20 percent lower than those in detached and semi-detached systems. We calculate the binary flares activity level (AL) of all the flare binaries, and discuss its variations along the orbital period (P_orb) and rotation period (P_rot, calculated for only detached binaries). We find that AL increases with decreasing P_orb or P_rot up to the critical values at P_orb near 3 days or P_rot near 1.5 days, thereafter, the AL starts decreasing no matter how fast the stars rotate. We examine the flaring rate as a function of orbital phase in 2 eclipsing binaries on which a large number of flares are detected. It appears that there is no correlation between flaring rate and orbital phase in these 2 binaries. In contrast, when we examine the function with 203 flares on 20 non-eclipse ellipsoidal binaries, bimodal distribution of amplitude weighted flare numbers shows up at orbital phase 0.25 and 0.75. Such variation could be larger than what is expected from the cross-section modification.