log(L/L_⊙) vs. age (in Myr) for the sequence with 0.2025 M_⊙, corresponding to the last instability region. The temporal evolution of the surface luminosity (green line), the luminosity given by the pp chain (light-blue dashed line), and the luminosity due to the CNO bicycle (red dotted line) are shown, along with the ninth instability region emphasized by a thick black line. Grey vertical strips mark the narrow regions where convection is present (either internal or external). A blue number indicates the number of the flash (as in Fig. 1), while the cyan diamond indicates the location of the template model analyzed in Fig. 5 (and Fig. 1).