Evolution of the internal temperature T and the chemical imbalance η_npe for a 1.68 M_⊙ star built with the EOS BPAL21 and no muons, with the initial condition T = 10⁹ K and null chemical imbalance. The spin-down is assumed to be caused by the magnetic dipole radiation, with dipolar field strengths B = 10¹¹ G (dashed line) and B = 10¹² G (solid line) initial period of P₀ = 5 ms. The dotted-dashed line indicates the energy gap Δ_n = 0.05 MeV.