Location of PG 1034+001 and PG 0038+199 in the g–T_eff  diagram (circles with error bars) among other DO white dwarfs, PG 1159 stars, and O(He) stars. Evolutionary tracks from Althaus et al. (2009) are labeled with the stellar mass in M_⊙. Indicated is the PG1159 wind limit according to Unglaub & Bues (2000). Below it, no PG 1159 stars are found because radiation-driven stellar winds become so weak that they can no longer prevent gravitational settling of heavy elements.