Constraining the third dredge-up via carbon stars in the Magellanic Clouds

We use the available data for Magellanic Cloud carbon stars to constrain the efficiency of the third dredge-up process in TP-AGB models. We show that star counts in LMC clusters provide quite stringent limits to the lifetime of the C-star phase, with a duration between 2 and 3 Myr for stars in the mass range from similar to 1.5 to 2.8 Mcircle dot. Together with the luminosity functions of field C stars, this information allows us to re-calibrate the third dredge-up parameters logT(b)(dred) and lambda in TP-AGB models that include variable molecular opacities (Marigo 2002). Preliminary results are presented here.