Surface gravity – effective temperature diagram for ELM white dwarf sequences with 0.15540, 0.16115, 0.16499, 0.17064, 0.17624 M_⊙ (thick lines, from right to left), together with the lowest mass He-core white dwarf sequence that undergoes CNO flashes (0.18213 M_⊙, thin line). Tracks correspond to the first 7 Gyr of evolution after the end of mass loss when the secondary shrinks within its Roche lobe. The color scale to the right displays the cooling age in Gyr. We note the much faster evolution of the 0.18213 M_⊙ sequence after the occurrence of the CNO flashes. Black and grey circles represent observed nonpulsating post-RGB low-mass stars, and red asterisks represent pulsating ELM white dwarfs, as detailed in Table 2.