Locations of our targets in the Kiel diagram (left) and HRD (right). The black dashed and solid lines are stellar evolutionary tracks for He-, CO-core WD, respectively (Renedo et al. 2010; Hall et al. 2013), corresponding to masses of 0.306, 0.378, 0.452, 0.524, 0.570, 0.632, 0.767, and 0.934 M_⊙. The gray solid lines are VLTP post-AGB evolutionary tracks form Althaus et al. (2009) for masses of 0.514, 0.565, 0.609, 0.741, and 0.869 M_⊙. The gray, thick, dashed line is a 1.10 M_⊙ H-deficient ONe-Core WD track from Camisassa et al. (2019). The purple solid line indicates where the He abundances should have decreased down to log(He/H) = −3 according to predictions of Unglaub & Bues (2000).