Improved Age Estimation for Solar‐Type Dwarfs Using Activity‐Rotation Diagnostics

While the strong anticorrelation between chromospheric activity and age has led to the common use of the Ca II H K emission index (R'_(HK) = L_(HK)/L_(bol)) as an empirical age estimator for solar-type dwarfs, existing activity-age relations implausible ages at both high and low activity levels.We have compiled R'_(HK) data from the literature young stellar clusters, richly populating for the first time the young end of the activity-age relation. Combining the activity data with modern cluster age estimates and analyzing the color dependence of the chromospheric activity index,we derive an improved activity-age calibration for F7-K2 dwarfs (0:5 mag < B - V < 0.9 mag). We present a more fundamentally motivated activity-age calibration that relies on conversion of R'_(HK) values through Rossby number to rotation periods and then makes use of improved gyrochronology relations. We demonstrate that new activity-age calibration has typical age precision of ~0.2 dex for normal solar-type dwarfs aged between the and the Sun (~0.6-4.5 Gyr). Inferring ages through activity-rotation-age relations accounts for some color-dependent and systematically improves the age estimates (albeit only slightly). We demonstrate that coronal as measured through the fractional X-ray luminosity (R_X = L_X/L_(bol)) has nearly the same age- and rotation inferring as chromospheric activity measured through R'_(HK). As a first application of our calibrations, we new activity-derived age estimates for a volume-limited sample of the 108 solar-type field dwarfs within 16 pc.