Core carbon mass fraction X_C as a function of (a) initial mass M_ini and (b) CO core mass M_CO at the end of core helium burning. The initial masses M_ini of single stars corresponding to M_CO are provided at the top of panel b (cf. Fig. 3). The light-grey shading indicates radiative core carbon burning and the darkish-grey shading indicates radiative core neon burning. The dashed (dotted) lines show the core carbon mass fractions at the end of core helium burning below which our models burn carbon (neon) in their cores radiatively. In panel b, we zoom in on the two branches and the ranges in X_C and M_CO do not correspond directly to those in panel a.