CALIBRATION OF STELLAR MODELS

We discuss the need for a new calibration of the mixing-length paramet er owing to the inclusion of updated opacity in the computation of low -mass stellar models. When the contribution to the opacity of molecule s is properly taken into account, a significantly larger value of the mixing length is required in order to reproduce the observed radii of the stars. In addition, at variance with previous claims, we find that different stellar models require different values of l/H-p. In partic ular we report some evidences of a correlation between mixing length a nd metallicity.