Kepler rapidly rotating giant stars

TL;DR

This paper reports the discovery of 17 rapidly rotating giant stars observed by Kepler, revealing their unusually short rotation periods and potential infrared excess, which may indicate stellar coalescence or accretion events.

Contribution

First direct measurement of rapid rotation in giant stars using Kepler photometry, expanding understanding of stellar evolution and surface rotation rates.

Findings

Rotation periods range from 13 to 55 days.

Surface rotation rates up to 18 times the Sun.

Infrared excess observed in at least half of the stars.

Abstract

Rapidly rotating giant stars are relatively rare and may represent important stages of stellar evolution, resulting from stellar coalescence of close binary systems or accretion of sub-stellar companions by their hosting stars. In the present letter we report 17 giant stars observed in the scope of the Kepler space mission exhibiting rapid rotation behavior. For the first time the abnormal rotational behavior for this puzzling family of stars is revealed by direct measurements of rotation, namely from photometric rotation period, exhibiting very short rotation period with values ranging from 13 to 55 days. This finding points for remarkable surface rotation rates, up to 18 times the Sun rotation. These giants are combined with 6 other recently listed in the literature for mid-IR diagnostic based on WISE information, from which a trend for an infrared excess is revealed for at least a half of the stars, but at a level far lower than the dust excess emission shown by planet-bearing main-sequence stars.