Locations of the O(He) star J0757 (red triangle with error bars) and the PG 1159 star J1556 (black inverted triangle with error bars) and other PG 1159 and O(He) stars (black inverted triangles and red triangles, respectively, De Marco et al. 2015; Reindl et al. 2014b; Werner & Rauch 2014; Werner et al. 2014; Gianninas et al. 2010; Wassermann et al. 2010; Werner & Herwig 2006) in the T_eff−log g diagram. Their likely successors, the H-deficient white dwarfs (Reindl et al. 2014a; Werner et al. 2014; Mahsereci 2011; Hügelmeyer et al. 2006; Dreizler & Werner 1996) are indicated by filled-in red squares. The upper panel compares the location of these stars to (V)LTP evolutionary tracks (gray lines) of Miller Bertolami & Althaus (2007, 2006). For clarity, only two tracks are labeled with stellar masses. Intermediate tracks correspond to 0.530, 0.542, 0.565, 0.584, 0.609, 0.664, 0.741 M_⊙. The lower panel compares only the locations of the C-rich O(He) stars (red triangles) and C-strong lined He-sdO stars (red rhombs) from the sample of Geier et al. (2015) with post-double He white dwarf merger tracks (purple lines) of Zhang & Jeffery (2012a,b).