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Title:
The Uncertainties in the Age of Globular Clusters from Their Helium Abundance and Mass Loss
Authors:
Shi, Xiangdong
Publication:
Astrophysical Journal v.446, p.637 (ApJ Homepage)
Publication Date:
06/1995
Origin:
APJ; KNUDSEN
Astronomy Keywords:
GALAXY: GLOBULAR CLUSTERS: GENERAL, STARS: ABUNDANCES, STARS: EVOLUTION, STARS: MASS LOSS
DOI:
10.1086/175823
Bibliographic Code:
1995ApJ...446..637S

Abstract

The age of globular clusters inferred from observations depends sensitively on assumptions such as the initial helium abundance and the mass-loss rate. A high helium abundance (e.g., Y ≈ 0.28), as well as an inclusion of helium diffusion and oxygen-enhancement in stellar models, can lower the current age estimate for metal-poor globular clusters from 14±1.5 Gyr to obtain 11±1 Gyr, significantly relaxing the constraints on the Hubble constant, allowing values as high as 60 km s-1 Mpc-1 for a universe with the critical density and 90 km s-1 Mpc-1 for a baryon-only universe. The uncertainties of a high helium abundance and an instability strip induced mass loss near the turn-off in globular clusters are discussed. Ages lower than 10 Gyr are not possible even with the operation of both of these mechanisms unless the initial helium abundance in globular clusters is greater than 0.28, which can hardly be accommodated by indirect inferences of helium abundances in globular clusters.

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Database: Astronomy
Physics
arXiv e-prints