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Proc Natl Acad Sci U S A. 1998 Jan 6;95(1):13-7.

Globular cluster ages.

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Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, United Kingdom.


We review two new methods to determine the age of globular clusters (GCs). These two methods are more accurate than the classical isochrone fitting technique. The first method is based on the morphology of the horizontal branch and is independent of the distance modulus of the globular cluster. The second method uses a careful binning of the stellar luminosity function and determines simultaneously the distance and age of the GC. We find that the oldest galactic GCs have an age of 13.5 +/- 2 gigayears (Gyr). The absolute minimum age for the oldest GCs is 10.5 Gyr (with 99% confidence) and the maximum 16.0 Gyr (with 99% confidence). Therefore, an Einstein-De Sitter Universe (Omega = 1) is not totally ruled out if the Hubble constant is about 65 +/- 10 Km s-1 Mpc-1.

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