On Ca II Emission as an Indicator of the Age of Young Stars

Chromospheric emission in the Ca II H and K lines has often been used as an age diagnostic for solar mass stars. For 20 such stars with ages less than a few hundred megayears, we compare Ca II ages derived by Wright et al. with ages we derive based on a combination of lithium abundance, X-ray activity, and Galactic space motion. Typically, the Ca II ages are noticeably older than the lithium/X-ray ages, suggesting that a recalibration of the Ca II ages may be necessary