The W-function applied to the age of Globular Clusters

We present a statistical approach for estimating the age of Globular Clusters by measurement of the likelihood between the observed cluster sequences in the Colour--Magnitude Diagram and the synthetic cluster sequences computed from stellar evolutionary models. In the conventional isochrone fitting procedure, the age is estimated in a subjective way. Here, we calculate the degree of likelihood by applying a modern statistical estimator, the Saha estimator {\it W}, and the interval of confidence from $\chi^{2}$ statistics. We apply this approach to sets of three different evolutionary models. Each of these sets consists of different chemical abundances, ages, input physics, etc. Based on our approach, we estimate the age of NGC 6397, M92 and M3. With a confidence level of 99%, we find that the best estimate of the age is 14.0 Gyr within the range of 13.8 to 14.4 Gyr for NGC 6397, 14.75 Gyr within the range of 14.50 to 15.40 Gyr for M92, and 16.0 Gyr within the range of 15.9 to 16.3 Gyr for M3.