Luminosity of the RGB tip (i.e., when helium ignition occurs) as a function of initial stellar mass and Y_ini. The black line delimits the domains where helium ignition (when it occurs) starts with a flash or in non-degenerate conditions. The colors indicate the luminosity of the RGB tip, with white dashed lines being isochrones with MS turn-off ages indicated in Gyr; the white area corresponds to the domain where stellar models predict main sequence lifetimes higher than 13.8 Gyr.