HRD of PNe nuclei together with evolutionary tracks of hydrogen-burning AGB remnant after Miller Bertolami & Althaus (2006, priv. comm., solid). Numbers at the tracks denote the central-star masses in solar units. Tracks of AGB remnants from Blöcker (1995) and Schönberner (1983) are also shown (dashed) for comparison. Their masses are (from bottom to top): 0.553, 0.565, 0.605, and 0.696 M_⊙, respectively. The 0.517 and 0.553 M_⊙ remnants start their post-AGB evolution as burning helium. The upward “hooks” are due to the rekindling of hydrogen which then slows down the evolution considerably. The filled circles with the respective error bars mark the positions of the Milky Way disk objects listed in Table 8. We show also nine (hydrogen-rich) objects from the Magellanic Clouds (seven from the Large Cloud, circles, and two from the Small Cloud, squares), taken from the analyses of Herald & Bianchi (2004) and Herald & Bianchi (2007). Also, five objects from the Milky Way bulge with the parameters derived by Hultzsch et al. (2007) are displayed (diamonds). The position of K648 in M 15 is based on the recent study of Jacoby et al. (2017).