Hertzsprung–Russell diagram including galactic WR stars of nitrogen (WN), carbon (WC), and oxygen sequences (WO). The solid shapes mark inferred core effective temperatures and luminosities from Hamann et al. (2019; WN) and Sander et al. (2019; WO,WC); the mean value is marked with a +. The x marks the location of the modified average luminosity and temperature, where the spectroscopically inferred core radius has been reduced by a factor of 3 (see text). The grey dashed line shows the approximate predicted location of the Helium Zero Age Main Sequence (He-ZAMS) computed using MESA (see the text).