Density profile in the degenerate helium core of models sharing similar values of ρ_c but different stellar parameters (blue curve: M = 1 M_⊙ and [Fe/H] = −0.4 dex, red curve: M = 1.4 M_⊙ and [Fe/H] = +0.4 dex). The dotted lines delimit the region of strong degeneracy for both models and the dash-dot lines indicate the location of the H-burning shell. The black dashed line corresponds to the density profile for a polytrope of exponent γ = 1.55.