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2010MNRAS.408..999D - Mon. Not. R. Astron. Soc., 408, 999-1005 (2010/October-3)
The helium spread in the globular cluster 47 Tuc.
DI CRISCIENZO M., VENTURA P., D'ANTONA F., MILONE A. and PIOTTO G.
Abstract (from CDS):
In this work we examine in detail whether the horizontal-branch morphology and subgiant structure provide further independent indications that a real - although very small - helium spread is present in the cluster. We reanalyse the HST archival data for the horizontal branch of 47 Tuc, obtaining a sample of ∼500 stars with very small photometric errors, and build a population synthesis based on new models to show that its particular morphology can be better explained by taking into account a spread in helium abundance of 2 per cent in mass. The same variation in helium is able to explain the spread in luminosity of the subgiant branch, while a small part of the second generation is characterized by a small C+N+O increase and provides an explanation for the fainter subgiant branch. We conclude that three photometric features concur to form the paradigm that a small but real helium spread is present in a cluster that has no spectacular evidence for multiple populations like those shown by other massive clusters. This work thus shows that multiple populations in globular clusters are increasingly confirmed to be ubiquitous.
Abstract Copyright: © 2010 The Authors. Journal compilation © 2010 RAS
Journal keyword(s): stars: evolution - stars: horizontal branch - globular clusters: general - globular clusters: individual: 47 Tuc
Simbad objects: 7
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