Relation between ΔΠ₁ and the central density ρ_c in the models of the grid presented in Sect. 3. Thick colored lines (resp. thin black lines) indicate periods of the evolution where electron degeneracy is strong (resp. weak) in the core. The color code is the same as in Fig. 2. The red dashed line corresponds to a linear regression of the ΔΠ₁ − ρ_c relation for stars with degenerate cores (see text).