Rotation periods of the Hyades open cluster using ASAS light curves : measuring the Hyades gyro-age and benchmarking tools for gyrochronology studies with LSST

Abstract

Rotation period distributions for older open clusters are difficult to obtain because of the general scarcity of clusters with ages greater than 200 Myr, as well as the challenge of measuring rotation periods for less active older stars. This has clouded our knowledge of how stars spin down as they evolve from the zero-age main sequence. A key piece of our understanding of how stellar rotation rates change over time relies on the study of the nearby (~45 pc) and old (~625 Myr) Hyades open cluster. We present the results from a detailed analysis of the rotation period distribution of the Hyades in an effort to estimate the gyro-age of this benchmark open cluster. Analyzing All Sky Automated Survey (ASAS) light curves with 14+ year baselines, we measure rotation periods for Hyades members by applying a period-finding technique that combines the Lomb-Scargle periodogram and Monte Carlo simulations to optimize period detection in long-baseline, low-cadence light curves that potentially suffer from time-dependent changes, e.g. star spot evolution. We derive 67 rotation periods for Hyades members, 40 of which are determined for the first time. These rotation periods measured from ASAS light curves allow us to characterize the rotation period distribution of the Hyades, enabling the application of current gyrochronology models to calculate a rotation-age for the cluster. Additionally, using ASAS data provides a valuable test of our ability to determine rotation periods in future low-cadence, extended duration surveys, such as the Large Synoptic Survey Telescope (LSST).