Rotation of young solar-type stars as seen by Gaia and K2

TL;DR

This study cross-validates stellar rotation measurements from Gaia and K2 missions, revealing their reliability and biases, especially for young, late-type stars, and highlights differences in activity detection capabilities.

Contribution

It provides an external validation of Gaia rotation data using K2 observations and analyzes the biases and limitations of both datasets for stellar rotation studies.

Findings

K2 and Gaia measurements agree for most stars

K2 misses ultra-fast rotators identified by Gaia

Young late-type stars are prominent in both datasets

Abstract

Accurate surface rotation measurements are crucial to estimate stellar ages and improve our understanding of stellar rotational evolution. Comparisons of datasets obtained from different space missions on common targets represent in this sense a way to explore the respective biases and reliability of the considered instruments, as well as a possibility to perform a more in-depth investigation of the properties of the observed stars. In this perspective, we aim at using observations for the K2 mission to provide an external validation to Gaia rotation measurements, and confront observables available from Gaia, K2, and Kepler. We therefore crossmatch the Gaia rotation catalogue and the K2 mission Ecliptic Plane Input Catalogue (EPIC) in order to find Gaia stars with both measured rotation and periods and available K2 light curves. Using our crossmatch, we analyse 1063 light curves from the K2 mission in order to characterise stellar rotational modulations and compare the recovered periods with Gaia reference values. The K2/Gaia cross-validated sample is used as a random-forest classifier training set to identify a subsample of Gaia stars with similar properties. We validate the Gaia rotation measurements for a large fraction of the sample and we discuss the possible origin of the discrepancies between some K2 and Gaia measurements. We note that the K2 sample does not include members of the low-activity ultra-fast-rotating (UFR) population that was highlighted by Gaia observations, a feature that we explain considering the instrumental capabilities of K2. Placing our sample in perspective with the full Gaia rotation catalogues and Kepler observations, we show that the population for which both Gaia and K2 are able to measure rotation is composed of young late-type stars, a significant fraction of which is not yet converged on the slow-rotator gyrochronological sequence. [abridged]