The Age of the Globular Cluster M68

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Abstract
Relying on the accurate color-magnitude diagram (CMD) presented by Walker in 1994, we use the fitting of moderately hot horizontal-branch models to the observed CMD to derive suitable information regarding both cluster reddening and distance modulus and to discuss theoretical predictions constraining the absolute age of the metal-poor Galactic globular cluster M68. As a first step, we show that such a procedure, when based on an "old" theoretical evolutionary scenario, agrees with similar evaluations already given in the literature, predicting an age of the order of 13-14 Gyr for the cluster. We show that adopting updated theoretical models, which include all recent improvements in the input physics and in which element diffusion is taken into account, decreases current estimates of the age of M68 to 10 Gyr. Possible sources of errors in our estimate are briefly discussed in light of recent results from the HIPPARCOS satellite. The relevance of comparing M68 with other metal-poor Galactic globular clusters is finally discussed, suggesting that the age of M68 could perhaps represent the common age of all these clusters and weakening considerably current claims for a conflict with cosmological ages.

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