LITHIUM IN M-67 - EVIDENCE FOR SPREAD IN A SOLAR AGE CLUSTER

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 sol ar-type stars belonging to this cluster. This implies that standard mo dels 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 ag e indicator for solar-type stars. The comparison of Li abundances in M 67 (age similar to 4.7 x 10(9) yrs) with those in the younger Hyades cluster (similar to 7 x 10(8) yrs) shows that the less depleted stars in M 67 have a Li content only similar to 0.25 dex below similar stars in the Hyades. Considering the similar to 4 Gyrs difference between t he two clusters, this indicates that standard lithium destruction mech anisms are very inefficient (if present at all) in many solar-type sta rs during most of their main sequence lifetime. On the other hand, alm ost 40% of our sample stars show a significant Li depletion, with valu es comparable to the Sun. Our sample also includes one SB2 binary, for which a very high Li abundance was previously reported. We found an a bundance significantly higher than in single stars, but our spectra ar e inconsistent with those previously published.