The TIME Table: rotation and ages of cool exoplanet host stars

Abstract

Age is a stellar parameter that is both fundamental and difficult to determine. Among middle-aged M dwarfs, the most prolific hosts of close-in and detectable exoplanets, gyrochronology is the most promising method to assign ages, but requires calibration by rotation-temperature sequences (gyrochrones) in clusters of known ages. We curated a catalog of 249 late K- and M-type (Teff=3200-4200K) exoplanet host stars with established rotation periods, and applied empirical, temperature-dependent rotation-age relations based on relevant published gyrochrones, including one derived from observations of the 4 Gyr-old open cluster M67. We estimated ages for 227 of these stars, and upper limits for 8 others, excluding 14 which are too rapidly rotating or are otherwise outside the valid parameter range of our gyrochronology. We estimated uncertainties based on observed scatter in rotation periods in young clusters, error in the gyrochrones, and uncertainties in temperature and non-solar metallicity. For those stars with measured metallicities, we provide but do not incorporate a correction for the effects of deviation from solar-metallicity. The age distribution of our sample declines to near zero at 10 Gyr, the age of the Galactic disk, with the handful of outliers explainable by large uncertainties. Continued addition or extension of cluster rotation sequences to more thoroughly calibrate the gyrochronology in time and temperature space, more precise and robust measurement of rotation periods, and more accurate stellar parameter measurements will enable continued improvements in the age estimates of these important exoplanet host stars.

Company for the Ultra-high Density, Ultra-short Period Sub-Earth GJ 367 b: Discovery of Two Additional Low-mass Planets at 11.5 and 34 Days*

“…We therefore conclude that GJ 367 is a rather slowly rotating, old star with a low magnetic activity level, rather than a young M dwarf. This conclusion is consistent with a recent study by Gaidos et al (2023), who measured an age of 7.95 ± 1.31 Gyr from the M-dwarf rotation-age relation.…”

The Empirical Limits of Gyrochronology

“…Clusters such as NGC 6791 (8 Gyr; Chaboyer et al 1999), or else a precise set of asteroseismic calibrators (e.g., van Saders et al 2016) might be the most plausible paths toward the goal of going older, though the complicating effects of stellar evolution for F and G dwarfs bear consideration. For M dwarf gyrochronology (e.g., Gaidos et al 2023), the existence of a slow-sequence for M67 implies that the M-dwarfs do eventually converge to a slow sequence; future studies should aim to determine when exactly this occurs.…”

Bioverse: The Habitable Zone Inner Edge Discontinuity as an Imprint of Runaway Greenhouse Climates on Exoplanet Demographics

“…While stellar ages are notoriously poorly constrained (Adams et al 2005), the age distribution of planet host stars in the Solar neighborhood was shown to be broadly consistent with uniform (Reid et al 2007;Gaidos et al 2023). For our synthetic stars, we thus drew random ages from a uniform distribution from 0 to 10 Gyr.…”