Hertzsprung-Russell diagram with evolutionary paths for non-rotating massive stars that enter at the end of their live the RGB (from Ekström et al. 2012). The grey dots correspond to the set of supergiants from Table 1. The lower set of lines (green) in the right part of the figure shows the Eddington luminosity, Eq. (15), calculated for silicate dust and for stellar masses of 10, 20, 30, and 50 M_⊙. The corresponding upper set of lines (blue) is for alumina dust. These limits are derived with the assumption that all Si or Al is condensed into their respective dust components. For a lower fraction f of condensation the lines have to be scaled upwards ∝1∕f.