Temporal Evolution of the Scattering Polarization of the CaII IR Triplet in Hydrodynamical Models of the Solar Chromosphere

TL;DR

This study investigates how velocity gradients and shocks in the solar chromosphere influence the scattering polarization of the Ca II IR triplet, revealing significant effects on polarization signals and potential for magnetic field diagnostics.

Contribution

It provides a detailed analysis of the temporal evolution of scattering polarization in dynamic chromospheric models, incorporating velocity effects and assessing observational feasibility.

Findings

Velocity gradients significantly enhance polarization amplitudes.

Shocks affect the temporal profiles of polarization signals.

Feasibility of observing polarization variations with large telescopes is confirmed.

Abstract

Velocity gradients in a stellar atmospheric plasma have an impact on the anisotropy of the radiation field that illuminates each point within the medium, and this may in principle influence the scattering line polarization that results from the induced atomic level polarization. Here we analyze the emergent linear polarization profiles of the Ca II infrared triplet after solving the radiative transfer problem of scattering polarization in time-dependent hydrodynamical models of the solar chromosphere, taking into account the impact of the plasma macroscopic velocity on the atomic level polarization. We discuss the influence that the velocity and temperature shocks in the considered chromospheric models have on the temporal evolution of the scattering polarization signals of the Ca II infrared lines, as well as on the temporally averaged profiles. Our results indicate that the increase of the linear polarization amplitudes caused by macroscopic velocity gradients may be significant in realistic situations. We also study the effect of the integration time, the microturbulent velocity and the photospheric dynamical conditions, and discuss the feasibility of observing with large-aperture telescopes the temporal variation of the scattering polarization profiles. Finally, we explore the possibility of using the differential Hanle effect in the IR triplet of Ca II with the intention of avoiding the characterization of the zero-field polarization to infer magnetic fields in dynamic situations.