New method for determining Doppler widths

An explicit analytical relation between the absorption-line profile and the emergent intensity is developed for a stellar atmosphere in which the absorption profile and the source and sink terms of the source function are depth-independent. Using this relation, a method is described for determining the Doppler width of the solar chromospheric Hα absorption profile, for which it is known that the source and sink terms are indirectly controlled by radiation fields external to the line-forming zone. Good agreement is found between the Doppler width derived for solar Hα and previous results. Finally, the method for determining the Doppler width is generalized for application to stellar spectra