Evolution of ﹩{T}_{{\rm{c}}}﹩ and ﹩{\rho }_{{\rm{c}}}﹩ in solar metallicity, non-rotating M_i = 15 and 30 ﹩{{\rm{M}}}_{\odot }﹩ pre-supernova models. The curves are calculated using an in situ 204 isotope reaction network. Locations of the core carbon, neon, oxygen, and silicon ignition are labeled, as is the scaling relation ﹩{T}_{{\rm{c}}}^{3}\propto {\rho }_{{\rm{c}}}﹩, and the ﹩{E}_{{\rm{F}}}/{k}_{{\rm{B}}}T\approx 4﹩ electron degeneracy curve. Regions dominated by electron–positron pairs, photodisintegration, and rapid electron capture are shaded and labeled.