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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 (RX = LX/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.
Mamajek et al. (Fri,) studied this question.