Variation in the luminosity as a function of slope s for different values of X_H for Z = 0.008. The parameter M_tot is fixed to 5 M_⊙. The abscissa goes from a fully chemically homogeneous model (s = 0) to a pure-He model (s = ∞). The minimum and maximum luminosities for a given total mass and surface X_H are marked by coloured dots and squares, respectively. The green dot indicates the luminosity of the 5 M_⊙ pure-He model.