Abundance profiles of the SERIES I 2.5 M_⊙, Z = 0.02; f_OV = 0.0 stellar model. The top-left panel refers to the structure when log(ρ_c/g cm⁻³)≃9.0. The distribution of residual carbon from previous burning stages is visible. The top-right panel shows the final composition of this model. Ignition of residual carbon leads to thermonuclear explosion. The panel at the bottom shows the final structure of the same model, in the case where carbon-consuming nuclear reactions have been turned off. In this scenario, the core reaches the density threshold for e-captures on Ne nuclei to commence, leading to formation of ²⁰O, and most likely to an ECSN.