Spectroscopic Hertzsprung–Russel diagram including data for SGXBs from Conti (1978; green crosses) and Falanga et al. (2015; blue crosses). The name of the source is added to the symbols. The parentheses include the donor masses as measured by Conti (1978) and Falanga et al. (2015). The grey dashed lines are tracks from single-star evolutionary models (Brott et al. 2011). The grey numbers indicate the initial mass of the corresponding stellar model. Red and orange lines indicate the evolution of our binary models. The starting point of each model is labelled with a blue star. The black dots correspond to time steps of 50 000 years.