期刊
ASTROPHYSICAL JOURNAL
卷 712, 期 1, 页码 527-535出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/712/1/527
关键词
globular clusters: general; stars: evolution; stars: horizontal-branch; stars: Population II
资金
- Monte dei Paschi di Siena
- PRIN-MIUR2007
- Fondecyt [1085278]
- FONDAP Center for Astrophysics [15010003]
- Basal CATA [PFB-06]
- Science and Technology Facilities Council [ST/H002391/1, PP/E001149/1] Funding Source: researchfish
- STFC [ST/H002391/1, PP/E001149/1] Funding Source: UKRI
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.
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