The Evolution of the Lithium Abundances of Solar-Type Stars. VIII. M67 (NGC 2682)

We have used the HIRES spectrograph on the Keck 10 m telescope to obtain echelle spectra of 25 solar-type stars in the old open cluster M67 (NGC 2682) and have used these spectra to derive lithium abundances. This cluster, which has approximately the same age and composition as the Sun, shows a pattern of Li depletion different from either the Pleiades or the Hyades. At M ≲ 1 M⊙, M67 is more Li depleted than the Hyades. For ∼1 M⊙ stars, M67 shows a significant spread in Li, with about two-thirds of the stars being Li-rich and the remainder Li-poor. The data are consistent with M67 having the same initial Li abundance as the initial solar abundance. This is further evidence that Li depletion in solar-type stars occurs during their main-sequence lifetimes, although at a slower rate than pre–main-sequence depletion. These M67 observations also indicate that a 1 M⊙ star at the Sun's age can have an Li abundance within a range of ∼1 dex, and that the Sun is not necessarily representative of all stars of its mass, age, and composition.