Tidal Synchronization and Differential Rotation of Kepler Eclipsing Binaries

TL;DR

This study analyzes Kepler eclipsing binaries to understand tidal synchronization, differential rotation, and stellar activity, revealing a transition in synchronization at 10 days and identifying new pulsators and a candidate RS CVn system.

Contribution

It provides the largest homogeneous dataset on tidal synchronization in late-type stars, including new rotation periods, differential rotation insights, and identification of new pulsators and a candidate RS CVn system.

Findings

79% of short-period EBs are synchronized

Existence of differential rotation causing slower rotation in some EBs

Transition from circular to eccentric binaries at 10 days

Abstract

Few observational constraints exist for the tidal synchronization rate of late-type stars, despite its fundamental role in binary evolution. We visually inspected the light curves of 2278 eclipsing binaries (EBs) from the Kepler Eclipsing Binary Catalog to identify those with starspot modulations, as well as other types of out-of-eclipse variability. We report rotation periods for 816 EBs with starspot modulations, and find that 79% of EBs with orbital periods less than ten days are synchronized. However, a population of short period EBs exists with rotation periods typically 13% slower than synchronous, which we attribute to the differential rotation of high latitude starspots. At 10 days, there is a transition from predominantly circular, synchronized EBs to predominantly eccentric, pseudosynchronized EBs. This transition period is in good agreement with the predicted and observed circularization period for Milky Way field binaries. At orbital periods greater than about 30 days, the amount of tidal synchronization decreases. We also report 12 previously unidentified candidate $\delta$ Scuti and $\gamma$ Doradus pulsators, as well as a candidate RS CVn system with an evolved primary that exhibits starspot occultations. For short period contact binaries, we observe a period-color relation, and compare it to previous studies. As a whole, these results represent the largest homogeneous study of tidal synchronization of late-type stars.