log T_eff − log g diagrams for the He-core WD sequences computed in Althaus et al. (2013). Sequences with masses in the range 0.18 ≲ M_∗ ≲ 0.4 undergo CNO flashes during the early-cooling phase, which leads to the complex loops in the diagram. Green squares and magenta triangles correspond to the observed post-RGB low-mass stars from Silvotti et al. (2012) and Brown et al. (2013), and filled blue circles correspond to the five pulsating low-mass WDs detected so far (Hermes et al. 2013a). Numbers in the left upper corner of each panel correspond to the stellar mass at the WD stage.