Thinkshop 16

The rotation periods of cool stars: Measurements, uses, connections and prospects

23rd - 26th September 2019

Talk

Stellar rotation along the ecliptic -- K2 reveals a variability decrease at ages between 600-800Myr

Timo Reinhold, Max Planck Institute for Solar System Research (MPS)

Rotation period measurements in the Kepler field have revealed a lack of stars with intermediate rotation periods, accompanied by a decrease of photometric variability. The K2 mission provides the opportunity to measure stellar rotation and photometric variability along different fields in the ecliptic plane. Analyzing K2 campaigns 0-18, a large data set covering more than 500,000 stars, we detect rotation periods in about 33,000 stars. The period distribution shows some bimodality, although less pronounced as observed in Kepler. Additionally, we find a local minimum of the stellar variability amplitude at rotation periods close to the "dip" of the period distribution. The periods at the variability minimum correspond to gyrochronology ages between 600-800 Myr. Our results support the proposed idea of a cancellation of bright and dark surface features at these ages, leading to a non-detection of periodicity, along with a decrease of variability. We conclude that the previously observed dearth of rotation periods is not unique to the Kepler field of view, but rather represents a general manifestation of stellar activity.