X-ray luminosity (in the range 0.1–2.5 keV, and in units of L_bol) as a functionof Ṁ∕v_∞, for stellar models with photospheric and wind parameters as in Table 3, but mass-loss rates ranging in between 10⁻⁹ and 10^−4.5 M_⊙ yr⁻¹, and different assumptions on f_X(r) (see legend, and Table 4). The dotted lines display linear relations (with respect to the log–log scaling), with slopes m = 1 and 2, to guide the eye. Models to the left of and at the vertical dashed line are optically thin in the X-ray emitting region at all contributing frequencies, i.e., R₁ < R_min for energies between 0.1 and 2.5 keV. See text.