Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...446..637s&link_type=abstract
Astrophysical Journal v.446, p.637
Astronomy and Astrophysics
Astronomy
23
Galaxy: Globular Clusters: General, Stars: Abundances, Stars: Evolution, Stars: Mass Loss
Scientific paper
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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