Polarized line formation with J-state interference in the presence of magnetic fields: A heuristic treatment of collisional frequency redistribution

Abstract

An expression for the partial frequency redistribution (PRD) matrix for line scattering in a two-term atom, which includes the J-state interference between its fine structure line components is derived. The influence of collisions (both elastic and inelastic) and an external magnetic field on the scattering process is taken into account. The lower term is assumed to be unpolarized and infinitely sharp. The linear Zeeman regime in which the Zeeman splitting is much smaller than the fine structure splitting is considered. The inelastic collision rates between the different levels are included in our treatment. We account for the depolarization caused by the collisions coupling the fine structure states of the upper term, but neglect the polarization transfer between the fine structure states. When the fine structure splitting goes to zero, we recover the redistribution matrix that represents the scattering on a two-level atom (which exhibits only m-state interference --- namely the Hanle effect). The way in which the multipolar index of the scattering atom enters into the expression for the redistribution matrix through the collisional branching ratios is discussed. The properties of the redistribution matrix are explored for a single scattering process for an L=0 to 1 to 0 scattering transition with S=1/2 (a hypothetical doublet centered at 5000 A and 5001 A). Further, a method for solving the Hanle radiative transfer equation for a two-term atom in the presence of collisions, PRD, and J-state interference is developed. The Stokes profiles emerging from an isothermal constant property medium are computed.

Accepted for publication in Journal of Quantitative Spectroscopy and Radiative Transfer (JQSRT)

References in corpus (1)

• J-state interference signatures in the Second Solar Spectrum: Modeling the Cr I triplet at 5204-5208 A

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• Master equation theory applied to the redistribution of polarized radiation in the weak radiation field limit. V. The two-term atom
• Modeling the quantum interference signatures of the Ba II D2 4554 A line in the second solar spectrum
• Polarized light scattering with Paschen-Back effect, level-crossing of fine structure states and partial frequency redistribution