Rayleigh Scattering in Spectral Series with L-Term Interference

TL;DR

This paper develops a formalism to analyze polarized radiation scattering across spectral series, highlighting the impact of radiation-induced coherence and partial frequency redistribution on polarization, especially in the solar continuum.

Contribution

It generalizes previous models to include multiple Λ-type atomic systems, revealing significant polarization effects due to coherence among spectral series terms.

Findings

Predicts 100% polarization in the far wings of complete spectral series

Shows importance of partial frequency redistribution and coherence effects

Provides a formalism applicable to various spectral series like Lyman, Balmer, and UV multiplets

Abstract

We derive a formalism to describe the scattering of polarized radiation over the full spectral range encompassed by atomic transitions belonging to the same spectral series (e.g., the H I Lyman and Balmer series, the UV multiplets of Fe I and Fe II). This allows us to study the role of radiation-induced coherence among the upper terms of the spectral series, and its contribution to Rayleigh scattering and the polarization of the solar continuum. We rely on previous theoretical results for the emissivity of a three-term atom of the $\Lambda$-type taking into account partially coherent scattering, and generalize its expression in order to describe a "multiple $\Lambda$" atomic system underlying the formation of a spectral series. Our study shows that important polarization effects must be expected because of the combined action of partial frequency redistribution and radiation-induced coherence among the terms of the series. In particular, our model predicts the correct asymptotic limit of 100% polarization in the far wings of a \emph{complete} (i.e., $\Delta L=0,\pm 1$) group of transitions, which must be expected on the basis of the principle of spectroscopic stability.