While the strong anticorrelation between chromospheric activity and age has led to the common use of the CaII H and K emission index (R'HK=L_HK_/L_bol_) 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<B-V<0.9mag). 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.

Cone search capability for table J/ApJ/687/1264/table5 (Members of stellar aggregates with logR'HK measurements)

Cone search capability for table J/ApJ/687/1264/table8 (Old solar-type dwarfs from Valenti et al. (2005, Cat. J/ApJS/159/141) with age uncertainties of <20%)

Cone search capability for table J/ApJ/687/1264/table13 (Activity ages for the solar-type dwarfs within 16pc)

Cone search capability for table J/ApJ/687/1264/binaries (log(R'HK) for solar-type dwarf binaries (tables 2 and 3 of paper))

Cone search capability for table J/ApJ/687/1264/table4 (Field binaries with rotation periods)

Cone search capability for table J/ApJ/687/1264/table12 (Activity-gyro ages for solar-type binaries)