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Context. A derivation of a generalized sqrt(epsilon)-law for nonthermalcollisional rates of excitation by charged perturbers is presented. Aims. Aimof this paper is to find a more general analytical expression for a surfacevalue of the source function which can be used as an addtional tool forverification of the non-LTE radiative transfer codes. Methods. Under the impactapproximation hypothesis, static, one-dimensional, plane-parallel atmosphere,constant magnetic field of arbitrary strength and direction, two-level atommodel with unpolarized lower level and stimulated emission neglected, weintroduce the unphysical terms into the equations of statistical equilibriumand solve the appropriate non-LTE integral equations. Results. We derive a newanalytical condition for the surface values of the source function componentsexpressed in the basis of irreducible spherical tensors.

astronomy and astrophysics

Generalized sqrt(epsilon)-law. The role of unphysical source terms in  resonance line polarization transfer and its importance as an additional test  of NLTE radiative transfer codes