THE AGES OF THE DISK CLUSTERS NGC-188, M67, AND NGC-752, USING IMPROVED OPACITIES AND CLUSTER MEMBERSHIP DATA

Theoretical isochrones have been constructed using the OPAL opacities to derive the ages of the open clusters NGC 188, M67, and NGC 752 as well as to estimate the amount of convective overshoot at the convective core edge. We find that - under the assumptions made in the models - no overshoot, or a very small amount (up to 0.1 Hp) is allowed for the best fits. Very good agreement is achieved between models and the main sequence, turnoff, subgiant, and giant branch for the clusters NGC 188 and M67. For NGC 188 and M67 we derive the ages: 6.0-0.5+1.0 Gyr and 4.0±0.5 Gyr, respectively, where the main uncertainty is due to the estimate of the interstellar reddening. The age of NGC 752 is 2.0-0.3+0.5 Gyr if the adopted metallicity is [Fe/H]=-0.27.