Sample WDs shown in the Kiel diagram (left) and HRD (right). Solid black line in the left panel corresponds to the theoretical wind limit by (Unglaub & Bues 2000). Dashed black lines in both panels represent predicted He abundance (N(He)/N(H) = 10⁻³) in the cooling sequence by the same authors, which also matches with the approximate optical detection limit of He. Green dotted lines (left: 0.525, 0.570, 0.593, 0.609, 0.632, 0.659, 0.705, 0.767, and 0.837 M_⊙, right: 0.525 - 0.935 M_⊙) represent evolutionary tracks of H-rich WDs (Z = 0.01) from Renedo et al. (2010).