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

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.

12 pages, 9 figures. Accepted for publication in ApJ. New figure added, typos corrected

References in corpus (3)

• A Substantial Amount of Hidden Magnetic Energy in the Quiet Sun
• Non-local thermodynamic equilibrium inversions from a 3D MHD chromospheric model
• Scattering polarization in the CaII Infrared Triplet with Velocity Gradients

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