The scattering polarization of the Ly-alpha lines of H I and He II taking into account PRD and J-state interference effects

TL;DR

This paper investigates the scattering polarization of Ly-alpha lines of H I and He II in the solar atmosphere, incorporating PRD and J-state interference effects, revealing complex polarization profiles sensitive to atmospheric temperature.

Contribution

It advances previous models by including PRD and J-state interference, showing their impact on polarization profiles and potential for solar atmospheric diagnostics.

Findings

Wing polarization signals are highly sensitive to temperature structure.

CRD approximation is adequate for core polarization amplitude estimation.

Complex polarization profiles are produced when including PRD and J-state interference.

Abstract

Recent theoretical investigations have pointed out that the cores of the Ly-alpha lines of H I and He II should show measurable scattering polarization signals when observing the solar disk, and that the magnetic sensitivity, through the Hanle effect, of such linear polarization signals is suitable for exploring the magnetism of the solar transition region. Such investigations were carried out in the limit of complete frequency redistribution (CRD) and neglecting quantum interference between the two upper J-levels of each line. Here we relax both approximations and show that the joint action of partial frequency redistribution (PRD) and J-state interference produces much more complex fractional linear polarization (Q/I) profiles, with large amplitudes in their wings. Such wing polarization signals turn out to be very sensitive to the temperature structure of the atmospheric model, so that they can be exploited for constraining the thermal properties of the solar chromosphere. Finally, we show that the approximation of CRD without J-state interference is however suitable for estimating the amplitude of the linear polarization signals in the core of the lines, where the Hanle effect operates.