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Title:
Ages of globular clusters and helium diffusion
Authors:
Chaboyer, Brian; Sarajedini, Ata; Demarque, Pierre
Affiliation:
AA(Yale University, New Haven, CT), AB(Yale University, New Haven, CT), AC(Yale University, New Haven, CT)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 394, no. 2, Aug. 1, 1992, p. 515-522. (ApJ Homepage)
Publication Date:
08/1992
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Gaseous Diffusion, Globular Clusters, Helium, Stellar Evolution, Astronomical Models, Galactic Structure, Metallicity, Milky Way Galaxy
DOI:
10.1086/171602
Bibliographic Code:
1992ApJ...394..515C

Abstract

Evolutionary tracks have been calculated with alpha-enhanced compositions which cover the entire globular cluster metallicity range and have constructed isochrones which include the effects of microscopic diffusion of helium. The turnoff magnitudes from the isochrones were combined with the theoretical RR Lyrae magnitudes from Lee to determine the ages of 32 Galactic globular clusters using the magnitude difference between the turnoff and horizontal branch. It is found that including the effects of helium diffusion has a negligible effect on the derived ages of globular clusters. Regardless of the inclusion of helium diffusion, a significant age spread of 5 Gyr among the globular clusters is found. The oldest globular clusters studied here are 17 +/- 2 Gyr old.

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