AN UPDATED THEORETICAL SCENARIO FOR GLOBULAR-CLUSTER STARS

In the first part of this paper we revisit the history of theoretical predictions for HE luminosities in old Population II stellar clusters, starting from the results of ''old'' evolutionary computations to int roduce in various steps all the available ''new'' physics. We discuss the influence of physical ingredients on selected evolutionary paramet ers, finally presenting models which incorporate all the most recent u pdating of the relevant physics. The evolutionary behavior of such mod els is extensively investigated for selected choices about the cluster metallicity, discussing theoretical predictions concerning both clust er isochrones and the calibration of the parameter R in terms of the o riginal amount of He in stellar matter. One finds that the ''new'' phy sics has a relevant influence on both these parameters, moving cluster ages into a much better agreement with current cosmological evaluatio ns. This scenario is implemented by a further set of stellar models wh ere element diffusion is taken into account. The comparison between th eoretical scenarios with or without diffusion is presented and discuss ed. A discussion of current observational constraints in the light of the updated theory closes the paper.