Evolution of the core density and temperature for M1 and M2. The dashed line shows the approximate boundary for electron degeneracy. Burning thresholds for a 100% abundance of the corresponding species are indicated with dotted lines. The NSE threshold assumes an equilibrium timescale of 1 s. In model M1b, the energy contribution of carbon-consuming reactions is set to zero (see text). M2b shows the core evolution of a 1.8 M_⊙ without overshooting. While this model stopped at log₁₀(ρ_c/g cm⁻³) ≃ 8.2 because of numerical convergence issues, the final core mass is similar to M2.