Emergent X-ray luminosities (in erg s^-1) as a function of Ṁ/v_∞. Supergiant models S30 (asterisks), S40 (triangles) and S50 (squares) with T_eff = 30, 40 and 50 kK, respectively, and mass-loss rates between 10^-9 and 2 × 10^-5M_⊙/ yr. All models have the same X-ray properties, f_x = 0.025, γ_x = 0.5, m_x = 20, and a maximum jump-velocity, u_∞ = 400km s^-1, corresponding to maximum shock temperatures of 2.3 × 10⁶ K. We calculated the X-ray luminosities in the range 0.1−2.5 keV (black, green, and turquoise) and in the range 0.35 to 2.5 keV (blue, red, and magenta). The dashed lines (no fits) serve as guidelines to check the predicted behavior for optically thin (red and green) and optically thick (black) conditions. (See text.)