A modified Eddington-Barbier relation in highly coherent resonance-line wings

It is shown that resonance-line wings are just as useful in inferring plane-parallel stellar chromospheric S sub L distributions as complete redistribution (CRD) profiles. Although coherent scattering effects at a given frequency tend to average depth-dependent parameters over a larger volume than in CRD, this effect can be offset by simply looking closer to line center, where the same depth-dependent information exists as in CRD, albeit somewhat more compressed in frequency space. For resonance lines with high excitation energies such as Ly-alpha, steep Planck function gradients can invalidate the modified Eddington-Barbier approach given, but this problem also exists in CRD.