Precision colour-magnitude diagram of M67

We have selected stars that are most likely to be single-star members of the cluster using proper motion, radial velocity, and variability information from the literature, and an examination of the most probable colour-magnitude diagram locations of unresolved stellar blends.

We have made detailed comparisons of our photometry of the selected stars with theoretical models, and discuss the most notable discrepancies. Observations of M67 turn-off stars are a severe test of algorithms attempting to describe convective cores in the limit of small extent, and we find strong evidence of a 'hook' just fainter than the turn-off gap. The stars in M67 support assertions that the degree of convective core overshooting decreases to zero for stars with masses in the range 1.0<(M/M_{sun}_)<=1.5, but that the degree of overshoot is smaller than currently used in published isochrones.