Instability domain corresponding to the ε mechanism on the log g vs. T_eff diagram for the low-mass WD sequence with 0.2025 M_⊙. The stages of pulsational instability are emphasized with thick black lines along the evolutionary tracks. Low-order g modes are driven before each flash. The track begins after the end of Roche-lobe overflow (upper right branch of the curve) and proceeds downward, toward higher values of T_eff, until the first CNO flash takes place. Numbers denote every consecutive flash. Red arrows along the curve indicate the course of the evolution. The cyan diamond before the ninth flash indicates the location of the template model analyzed in Fig. 5.