ON THE Δ<i>V</i><sub>HB</sub><SUP>bump</SUP> PARAMETER IN GLOBULAR CLUSTERS
No Thumbnail Available
Date
2010
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
We present new empirical estimates of the del 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 dex <= [M/H] <= -0.58 dex). Adopting the homogeneous metallicity scale provided either by Kraft & Ivans or by Carretta et al., we found that the observed del V-HB(bump) parameters are larger than predicted. In the metal-poor regime ([M/H] less than or similar to -1.7, -1.6 dex) 40% of GCs show discrepancies of 2s (approximate to 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 del V-HB(bump) parameters, in themetal- rich regime ([M/H] >= 0), might be systematically smaller than predicted.
Description
Keywords
globular clusters: general, stars: evolution, stars: horizontal-branch, stars: Population II