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.

ON THE Delta V(HB)(bump) PARAMETER IN GLOBULAR CLUSTERS

DEGL'INNOCENTI, SCILLA;PRADA MORONI, PIER GIORGIO;
2010

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.
Di Cecco, A; Bono, G; Stetson, Pb; Pietrinferni, A; Becucci, R; Cassisi, S; Degl'Innocenti, Scilla; Iannicola, G; PRADA MORONI, PIER GIORGIO; Buonanno, R; Calamida, A; Caputo, F; Castellani, M; Corsi, Ce; Ferraro, I; Dall'Ora, M; Monelli, M; Nonino, M; Piersimoni, Am; Pulone, L; Romaniello, M; Salaris, M; Walker, Ar; Zoccali, M.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/195552
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