The solution of several one-dimensional problems in nonstationary radiative transfer at frequencies in a spectral line is given. An approach based on searching for the unknowns in the form of Neumann series expansions is applied. The evolution of the line profile formed during reflection from a semi-infinite atmosphere is studied both with coherent and with fully incoherent scattering in the medium. The time dependence of the profiles formed at the boundaries of a finite atmosphere is also examined. In the two problems it is assumed that the atmosphere is illuminated by radiation either in the form of a δ(t) –pulse or by radiation with a unit intensity pulse. The solution takes into account both possible causes of time loss by photons during diffusion in the medium: the time spent by an atom in an excited state and the time lost by photons in passing between two successive scattering events. It is shown that with this general statement of the problem, the resultant probability density distribution function of the emerging radiation is given by a convolution of the distributions corresponding to the two components of the photon time expenditure.
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Translated from Astrofizika, Vol. 64, No. 4, pp. 537-550, November 2021.
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Nikoghossian, A.G. Time Dependent Radiative Transfer Problems in a One-Dimensional Medium. Astrophysics 64, 490–503 (2021). https://doi.org/10.1007/s10511-021-09710-2
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DOI: https://doi.org/10.1007/s10511-021-09710-2