Profile of the gas mean molecular weight of the envelope as a function of its temperature for Z = 0.7 when M_core = M_crit,NR(Z = 0.7). Solid lines: non-restricted case. Dotted lines: restricted case. We note that in the the non-restricted case, μ_gas decreases in the outer layers (i.e. low temperature values; see main text). The difference between both profiles at high temperatures is a consequence of a difference in the pressure-temperature profiles (see Fig. 5).