Chemical abundance distribution of hydrogen, helium, carbon, and oxygen in terms of the outer mass fraction for selected white dwarf models at the ZZ Ceti stage (thick lines) resulting from helium-enhanced progenitors with Z = 0.001 and initial helium abundance Y = 0.4. The chemical profiles at the beginning of the cooling track are the thin lines. Panel a) corresponds to a helium-core white dwarf resulting from a progenitor of initially M = 0.65 M_⊙, while panels b, c, and d) to C/O white dwarfs resulting from progenitors with M = 0.70 M_⊙, M = 0.75 M_⊙, and M = 1.0 M_⊙, respectively.