HR diagram with the positions of the BHGs (red diamonds) plotted with respect to the evolutionary tracks of Meynet & Maeder (2005) and the empirical HD limit. The position of HD 80077 assumes membership of Pismis 11 and hence a distance of 3.5 kpc (Marco & Negueruela 2009). The positions of other evolved stellar populations are also indicated: black squares – WN7-9h, O4-6 Ia and O4-6 If⁺ stars within the Arches; purple circles – galactic field BSGs; blue triangles – (candidate) LBVs and WNL stars; green stars – YHGs. Data from Martins et al. (2007, 2008), Crowther et al. (2006), Searle et al. (2008) and Clark et al. (in prep.).