Magellanic cloud star clusters : the problems of age determination, metallicity-age relationship and AGB star luminosity function.

In this paper we reanalyze the problem of age determination for relatively young globular clusters of the large Magellanic Cloud (LMC) in the light of the new evolutionary models incorporating convective overshooting studied by Bertelli et al. (1985). Ages are derived according to three methods, namely the main sequence termination magnitudes, the red giant star luminosities and the maximum AGB star luminosities. We find that the age discrepancy problem pointed out by Hodge (1983) does no longer exist with the new models. With the aid of the new clusters ages and metallicities collected from the literature, we delineate the [Fe/H] versus age relationship for LMC clusters. It seems that star formation in LMC occurred in two major episodes of activity, the most recent of which began about 4 1O⁹ yrs ago. Finally we apply the new stellar models to the problem of the asymptotic giant branch (AGB) star luminosity function of the LMC, recently derived by Reid and Mould (1984). In the classical scheme too many bright AGB stars are expected in the magnitude range -5 > M_b > -6 contrary to what observed. With the new stellar models a very satisfactory agreement between theory and observations is reached, without advocating rather ad hoc major changes in the efficiency of mass loss by stellar wind and/or superwind, star formation rate and initial mass function.