Transfer of resonance-line radiation in differentially expanding atmospheres. III. Formation of P Cygni-type lines by a double line or two partially "blended" lines.
We examine the transfer of resonance radiation in a spherically symmetric expanding stellar or quasi-stellar atmosphere in the case that the rest ("photospheric") position of one line (or line component) lies in the blueward absorption feature of another, under the simplifying assumptions of supersonic flow, atmosphere much larger than the central source, no occultation, no true absorption, and certain simplifications of the geometry. We find that for most optical depths and most reasonable choices of the velocity-radius relation, an emission peak is seen only for the redward component; only for small optical depths and wide doublet separation is a clear emission peak of the blue component formed within the absorption feature of the redward component. It is likewise difficult to find cases where between the rest locations of the two lines, the total light is less than that of the underlying continuum, unless the doublet separation exceeds approximately 0.4 of the total frequency spread of the absorption feature of either component. We have also treated cases where emission in the atmosphere is added to the scattered radiation. The effect is more to fill in the absorption features than to enhance the "emission" peaks. Using these results, we establish an upper limit to the N V optical depth in the expanding atmosphere of the QSO PHL 3200, and show that the outfiowing stellar winds in several hot supergiants in Orion probably involve a more graduate acceleration and less mass loss than heretofore postulated. Oradual acceleration is also indicated in Pup and Per. Subject headings: circumstellar shells - line formation - mass loss - quasi-stellar sources or objects - stellar winds