Positions of our program stars in the Kiel diagram, together with all known PG1159 stars (squares; see footnote 16) and three [WCE] stars (star symbols; NGC 1501, NGC 2371, and NGC 6905; see Sect. 5.2). Blue lines are VLTP post-AGB evolutionary tracks by Miller Bertolami & Althaus (2006) labeled with the mass in solar units. The black line indicates the PG1159 wind limit from Unglaub & Bues (2000), meaning that the mass-loss rate of the radiation-driven wind at this position of the evolutionary tracks becomes so weak that gravitational settling of heavy elements is able to remove them from the atmosphere. Thus, no PG1159 stars should be found at significantly lower temperatures. The dashed line is the wind limit assuming a mass-loss rate that is ten times lower.