HR diagram for Galactic stars. The top and bottom panels show stars with a hydrogen mass fraction of greater or smaller than 0.4, respectively. Filled triangles are sources analysed in the present study, while open triangles are literature data: WNh stars in the Arches cluster (Martins et al. 2008) and NGC3603-B (Crowther et al. 2010). Evolutionary tracks shown in red, green, cyan, and orange are from Ekström et al. (2012), Limongi & Chieffi (2018), Brott et al. (2011), and Grasha et al. (2021), respectively. The left and right panels show tracks with initial velocities of 150 and 300 km s⁻¹, respectively. In each panel, the range of hydrogen mass fraction is the same for the tracks and the observed stars. The bold part of the tracks is for a nitrogen mass fraction of greater than 0.0043, as explained in Fig. 5.