Sonic-point diagram associating the sonic-point temperature and the mass-loss rate to the contours of luminosity-to-mass ratio (for a metallicity 0.02 and a helium mass-fraction 0.48), color-coded according to the bar on the right side. The thick black line follows the contour indicating the possible sonic-point conditions of a star with L/M = 10^4.4 L_⊙/M_⊙. The white section of this contour and the gray shaded areas indicate the forbidden temperature range. The dot-dashed red line indicates the mass-loss prescription adopted in our numerical calculations.