Scattering polarization in the CaII Infrared Triplet with Velocity Gradients

Abstract

Magnetic field topology, thermal structure and plasma motions are the three main factors affecting the polarization signals used to understand our star. In this theoretical investigation, we focus on the effect that gradients in the macroscopic vertical velocity field have on the non-magnetic scattering polarization signals, establishing the basis for general cases. We demonstrate that the solar plasma velocity gradients have a significant effect on the linear polarization produced by scattering in chromospheric spectral lines. In particular, we show the impact of velocity gradients on the anisotropy of the radiation field and on the ensuing fractional alignment of the CaII levels, and how they can lead to an enhancement of the zero-field linear polarization signals. This investigation remarks the importance of knowing the dynamical state of the solar atmosphere in order to correctly interpret spectropolarimetric measurements, which is important, among other things, for establishing a suitable zero field reference case to infer magnetic fields via the Hanle effect.

14 pages, 10 figures, 3 appendixes, accepted for publication in ApJ

Cited by in corpus (10)

• The European Solar Telescope
• The magnetic sensitivity of the resonance and subordinate lines of Mg II in the solar chromosphere
• The Hanle and Zeeman polarization signals of the solar Ca II 8542 Å line
• Chromospheric diagnosis with Ca II lines: forward modeling in forward scattering (I)
• The effects of three-dimensional radiative transfer on the resonance polarization of the Ca I 4227 $\mathring{\mathrm{A}}$ line
• Constraining the shaping mechanism of the Red Rectangle through spectro-polarimetry of its central star
• Spatio-temporal evolution of Hanle and Zeeman synthetic polarization in a chromospheric spectral line
• The key role of solar dynamics in the chromospheric Hanle polarization
• Assessment of the CRD approximation for the observer's frame RIII redistribution matrix
• On the (mis)interpretation of the scattering polarization signatures in the Ca II 8542 A line through spectral line inversions