Theoretical isochrones from the MS to the tip of the RGB for the four different chemical compositions. The solid line corresponds to both the reference first-generation population and the second-generation population with the CNONa2 metal mixture (both with Y = 0.246), because they are virtually identical. The black dots along this isochrone denote the points for which we calculated the model atmosphere and synthetic spectra. The dashed line corresponds to the second- generation population with the CNONa1 metal mixture (Y = 0.246), while the dash-dotted line is for the same population, but for an initial He mass fraction of Y = 0.40.(See the text for more details.)