Explicit Form of the Radiative and Collisional Branching Ratios in Polarized Radiation Transport with Coherent Scattering

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Tuesday, October 17, 2017

We consider the vector emissivity of the polarized radiation transfer in a Lambda-type atomic transition, which we recently proposed in order to account for both CRD and PRD contributions to the scattered radiation. This expression can concisely be written as epsilon = [ epsilon^(1) - epsilon^(2)_{f.s.} ] + epsilon^(2) where epsilon^(1) and epsilon^(2) are the emissivity terms describing, respectively, one-photon and two-photon processes in a Lambda-type atom, and where “f.s.” means that the corresponding term must be evaluated assuming an appropriate “flat spectrum” average of the incident radiation across the spectral line. In this follow up study, we explicitly consider the expressions of these various terms for the case of a polarized multi-term atom, in order to derive the algebraic forms of the branching ratios between the CRD and PRD contributions to the emissivity. In the limit of a two-term atom with unpolarized lower-term, our results are shown to be in full agreement with those recently derived by Bommier (2017).

Schematic diagram showing the polarized radiation transfer in a Lambda-type atomic transition
Schematic diagram of the Lambda-type multi-term atom. In order to correctly describe the polarization properties of the outgoing light in the u → f transition, all lower terms li that are radiatively or collisionally connected to the upper term u, including the final term f, must be taken into account.

Publication Name: The Astrophysical Journal
First HAO Author's Name: Roberto Casini