Surface concentration of He as a function of T_eff in sdB stars. See the caption of Fig. 14 for the definition of the curves. Observations (circles) are from Geier et al. (2008), Geier et al. (2010) and Geier (2010, priv. commun.). The stars in red in Fig. 2 are also in red in this figure. The lines for He were stopped between X(He) = 0.001 and 0.0001 because the evaluation of the surface He abundance becomes inaccurate for smaller values.