Positions of the analyzed WN stars in the log T_∗-log R_t-plane. The labels refer to the BAT99 catalog. Different WN subtypes are distinguished by the shape of the symbols, as shown in the inlet. The hydrogen abundance is color-coded in three steps (undetectable, about 0.2, and about 0.4 mass fraction). The lower hatched part roughly indicates the region where the parameter space becomes degenerate because of large optical thickness of the wind. In this part, the stars can be shifted parallel to the gray lines without significant changes in the synthetic normalized emission line spectrum.