Regions and frequencies contributing to the line profiles of the B, C, and R lines (respectively for each column) in the wind model of Sect. 2. Shown here is a meridional cut in the half spherical stellar envelope of radius R_max = 10 R_c surrounding a stellar core of radius R_c. Displayed are the constant radial velocity surfaces (CRVSs) seen by an outside observer located at infinity on the right side of the figure for the three lines considered (left-right diagonal), as well as the displaced CRVSs of neighboring lines. The scale of the color bars is in km s⁻¹, and blue (red) indicates positive (negative) line frequencies.