1997A&A...325..535P

We present high resolution observations of main sequence stars in the solar age, solar metallicity open cluster M 67. For the first time we show conclusively that a spread in lithium abundances exists among solar-type stars belonging to this cluster. This implies that standard models with only convection as a mixing mechanism can hardly account for the spread at each colour, and that the Li abundance is not a good age indicator for solar-type stars. The comparison of Li abundances in M 67 (age ∼4.7x10⁹ yrs) with those in the younger Hyades cluster (∼7x10⁸ yrs) shows that the less depleted stars in M 67 have a Li content only ∼ 0.25 dex below similar stars in the Hyades. Considering the ∼ 4 Gyrs difference between the two clusters, this indicates that standard lithium destruction mechanisms are very inefficient (if present at all) in many solar-type stars during most of their main sequence lifetime. On the other hand, almost 40% of our sample stars show a significant Li depletion, with values comparable to the Sun. Our sample also includes one SB2 binary, for which a very high Li abundance was previously reported. We found an abundance significantly higher than in single stars, but our spectra are inconsistent with those previously published.