Linear Polarization Due to Lower Level Depopulation Pumping in Stellar Atmospheres

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Abstract
The possible generation of linear polarization in spectral lines due to depopulation-pumping processes in stellar atmospheres is investigated within the framework of a quantum electrodynamic theory for the transfer of polarized radiation based on the atomic density-matrix formalism. It is shown that the radiation field's anisotropy in solar-like atmospheres induces population imbalances among the lower level sublevels of optical line transitions. The depolarizing rates that are assumed to model some typical spectral lines are not capable of completely destroying such a lower level atomic alignment, and the corresponding linear polarization signals are found to lie above the sensitivity limit of some recently developed spectropolarimeters.