Kippenhahn diagrams showing the evolution of the stellar structure for our two example models at solar (left panels) and low (right panels) metallicity. They are shown using mass coordinate as the vertical axis (top panels) and radius coordinate (bottom panels). The horizontal axis indicates the time since helium depletion up to core carbon depletion. The black line represents the surface of the star. Regions of mixing by convection and overshooting are marked with double- and single-hatches, respectively. Colors indicate zones dominated by nuclear burning or neutrino cooling. See Fig. 1 and Sect. 3 for details and a discussion.