On the Delta V_HB_bump parameter in Globular Clusters
Abstract
We present new empirical estimates of the Delta V_HB_bump parameter for 15 Galactic globular clusters (GGCs) using accurate and homogeneous ground-based optical data. Together with similar evaluations available in the literature, we ended up with a sample of 62 GGCs covering a very broad range in metal content (-2.16<=[M/H]<=-0.58 dex). Adopting the homogeneous metallicity scale provided either by Kraft & Ivans (2004) or by Carretta et al. (2009), we found that the observed Delta V_HB_bump parameters are larger than predicted. In the metal-poor regime ([M/H]<=-1.7, -1.6 dex) 40% of GCs show discrepancies of 2sigma (~0.40 mag) or more. Evolutionary models that account either for alpha- and CNO-enhancement or for helium enhancement do not alleviate the discrepancy between theory and observations. The outcome is the same if we use the new Solar heavy-element mixture. The comparison between alpha- and CNO-enhanced evolutionary models and observations in the Carretta et al. metallicity scale also indicates that observed Delta V_HB_bump parameters, in the metal-rich regime ([M/H]=>0), might be systematically smaller than predicted.
Cite
@article{arxiv.1002.2074,
title = {On the Delta V_HB_bump parameter in Globular Clusters},
author = {A. Di Cecco and G. Bono and P. B. Stetson and A. Pietrinferni and R. Becucci and S. Cassisi and S. Degl'Innocenti and G. Iannicola and P. G. Prada Moroni and R. Buonanno and A. Calamida and F. Caputo and M. Castellani and C. E. Corsi and I. Ferraro and M. Dall'Ora and M. Monelli and M. Nonino and A. M. Piersimoni and L. Pulone and M. Romaniello and M. Salaris and A. R. Walker and M. Zoccali},
journal= {arXiv preprint arXiv:1002.2074},
year = {2015}
}