Hertzsprung-Russell diagram for our helium-enhanced evolutionary sequences for metallicity Z = 0.001 and initial helium mass fraction Y = 0.4. Evolutionary tracks for progenitors with initial stellar mass of 0.65 M_⊙, 0.70 M_⊙, 0.75 M_⊙, and 0.80 M_⊙ (panels a), b), c), and d), respectively) are depicted from the ZAMS to advanced stages of white dwarf evolution. The color scale on the right shows the fraction of the total luminosity from hydrogn burning. The upper value of the color scale has been set to 1.2, so higher values of L_{CNO + pp}/L_∗ are not shown.