Theoretical vs. semi-empirical relative ages of globular clusters

Abstract

Theoretical relative ages of galactic globular clusters have recently been challenged by a semi-empirical relation. It was used to point out that tested sets of isochrones were unable to reproduce the relation and yield internally inconsistent relative ages. We find that differential cluster ages derived with the isochrones by Salaris & Weiss (1998) are reliable and internally consistent. We also show that this consistency depends on using the lower absolute ages determined by SW98, which therefore receive more empirical support. Moreover, we discuss the effect of the clusters absolute age on the evaluation of their differential ages, and its connection with the question of their age dispersion.