Color–magnitude diagram for M 67 superposed upon the isochrone, which corresponds to an age of 3.87 Gyr. The red filled circles represent our work sample, i.e. stars with lithium abundance measurements. Stars with photometry available from Yadav et al. (2008), but with no lithium abundances, are displayed, for comparison with the isochrone, as black points. The squares represent the deviant stars. The roman numbers I − III are described in Sect. 5.1 and correspond to the temperatures of, respectively, 6095, 6123, and 4966 K.