Evaporation ages: A new dating method for young star clusters

Abstract

Context. The ages of young star clusters are fundamental clocks to constrain the formation and evolution of pre-main-sequence stars and their protoplanetary disks and exoplanets. However, dating methods for very young clusters often disagree, casting doubts on the accuracy of the derived ages. Aims. We propose a new method to derive the kinematic age of star clusters based on the evaporation ages of their stars. Methods. The method was validated and calibrated using hundreds of clusters identified in a supernova-driven simulation of the interstellar medium forming stars for approximately 40 Myr within a 250 pc region. Results. We demonstrate that the clusters’ evaporation-age uncertainty can be as small as about 10% for clusters with a large enough number of evaporated stars and small but with realistic observational errors. We have obtained evaporation ages for a pilot sample of ten clusters, finding a good agreement with their published isochronal ages. Conclusions. The evaporation ages will provide important constraints for modeling the pre-main-sequence evolution of low-mass stars, as well as allow for the star formation and gas-evaporation history of young clusters to be investigated. These ages can be more accurate than isochronal ages for very young clusters, for which observations and models are more uncertain.