SIMBAD references

We present Li abundances for 14 solar-type stars in the intermediate age (∼2Gyr) clusters IC 4651 and NGC 3680. The log[n(Li)] vs. effective temperature distributions are compared with those of the similar age cluster NGC 752, of the younger Hyades (600Myr) and of the older M 67 (4.5Gyr) and NGC 188 (6-7Gyr) clusters. Neither IC 4651 nor NGC 3680 show the dispersion in Li which is observed in M 67. The 2Gyr clusters have very similar Li vs. T_eff distributions; in addition, stars in the upper envelope of the M 67 distribution have the same Li content as stars in the 2Gyr clusters, suggesting that either they have not suffered any significant depletion between ∼2 and 4.5Gyr or they had a much slower Li depletion. Mechanisms that lead to Li depletion on the main sequence are discussed in the light of these observations. None of the existing models seem to reproduce well the observed features.