In the best observed Pleiades cluster, the luminosity function(LF) and mass function(MF) for main sequence(MS) stars extended to Mv ≈ 15.5(V≈21) are very similar to the initial luminosity function(ILF) and initial mass function(IMF) for field stars in the solar neighborhood showing a bump at log m≃-0.05 and a dip at log m ≃ -0.12. This dip is equivalent to the Wielen dip appearing in the LF for the field stars. The occurence of these bump and dip is independent of adopted mass-luminosity relation(MLR) . and their characteristics could be explained by a time-dependent bimodal IMF. The model with this IMF gives a total cluster mass of ~700M⊙, ~25 brown dwarfs and ~3 white dwarfs if the upper mass limit of progenitor of white dwarf is greater than 4.5M⊙. The cluster age on the basis of LF for brightest stars is given by ~ 8×107yr and all stars in the cluster lie along the single age sequence in the C-M diagram without showing a large dispersion from the sequence.

• LEE SEE WOO(Department of Astronomy, Seoul National University)
• SUNG HWANKYUNG(Department of Astronomy, Seoul National University)