Forward period spacing (ΔΠ) in terms of the periods of ℓ = 1 pulsation modes for a 1.10 M_⊙ WD model at T_eff ∼ 13 000 K (upper panels), ∼11 600 K (middle panels), and ∼10 000 K (lower panels) with an ONe core (left panels) and a CO core (right panels). In both set of models, latent-heat release and chemical redistribution caused by phase separation have been taken into account during crystallization (LH+PS case). The percentage of the crystallized mass are indicated. The horizontal dashed red line is the asymptotic period spacing.