Chemical yields from low- and intermediate-mass stars: Model predictions and basic observational constraints

In this work we analyse the role of low- and intermediate-mass stars in con tributing to the chemical enrichment of the interstellar medium. First we p resent new sets of stellar yields basing on the results of updated evolutio nary calculations, which extend from the ZAMS up to the end of the AGE phas e (Girardi et al. 2000; Marigo et al. 1999). These new yields, that present a significant dependence on metallicity, are then compared to those of oth er available sets (Renzini & Voli 1981; van de Hoek & Groenewegen 1997). Ti le resulting differences are explained in terms of different model assumpti ons - i.e. treatment of convective boundaries, mass loss, dredge-up, hot-bo ttom burning - and further discussed on the basis of important empirical co nstraints which should be reproduced by theory - i.e. the initial-final mas s relation, white dwarf mass distribution, carbon star luminosity function, and chemical abundances of planetary nebulae. We show that; present models are able to reproduce such constraints in a satisfactory way.