Rapidly Rotating, X-ray Bright Stars in the Kepler Field

Abstract

We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type FK, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, that is evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a process believed to produce the FK Com class of variable and their descendants. The FK Com stage, including the presence of an excretion disk, is short-lived but leads to longer-lived stages consisting of single, rapidly rotating evolved (sub)giants with high levels of stellar activity.

34 pages, Accepted in ApJ

References in corpus (7)

• The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
• Paper II: Calibration of the Swift ultraviolet/optical telescope
• Stellar Mergers Are Common
• Accurate early positions for Swift GRBS: enhancing X-ray positions with UVOT astrometry
• Rapid Rotation of Low-Mass Red Giants Using APOKASC: A Measure of Interaction Rates on the Post-main-sequence
• Kepler rapidly rotating giant stars
• On the Nature of Rapidly Rotating Single Evolved Stars

Cited by in corpus (5)

• Gaia Data Release 3: All-sky classification of 12.4 million variable sources into 25 classes
• Gaia Data Release 3: Cross-match of Gaia sources with variable objects from the literature
• Active red giants: close binaries versus single rapid rotators
• The Pseudosynchronization of Binary Stars Undergoing Strong Tidal Interactions
• Spectropolarimetric follow-up of 8 rapidly rotating, X-ray bright FK Comae candidates