Improved age estimation for solar-type dwarfs using activity-rotation diagnostics.
MAMAJEK E.E. and HILLENBRAND L.A.
Abstract (from CDS):
While the strong anticorrelation between chromospheric activity and age has led to the common use of the Ca II H and K emission index (R'HK=LHK/Lbol) as an empirical age estimator for solar-type dwarfs, existing activity-age relations produce implausible ages at both high and low activity levels. We have compiled R'HK data from the literature for young stellar clusters, richly populating for the first time the young end of the activity-age relation. Combining the cluster activity data with modern cluster age estimates and analyzing the color dependence of the chromospheric activity age index, we derive an improved activity-age calibration for F7-K2 dwarfs (0.5 mag<B-V<0.9 mag). We also present a more fundamentally motivated activity-age calibration that relies on conversion of R'HK values through the Rossby number to rotation periods and then makes use of improved gyrochronology relations. We demonstrate that our new activity-age calibration has typical age precision of ∼0.2 dex for normal solar-type dwarfs aged between the Hyades and the Sun (∼0.6-4.5 Gyr). Inferring ages through activity-rotation-age relations accounts for some color-dependent effects and systematically improves the age estimates (albeit only slightly). We demonstrate that coronal activity as measured through the fractional X-ray luminosity (RX=LX/Lbol) has nearly the same age- and rotation-inferring capability as chromospheric activity measured through R'HK. As a first application of our calibrations, we provide new activity-derived age estimates for a volume-limited sample of the 108 solar-type field dwarfs within 16 pc.