The Magnetic Sensitivity of the Resonance and Subordinate Lines of Mg II in the Solar Chromosphere

Abstract

We carry out a theoretical study of the polarization of the solar Mg ii h–k doublet (including its extended wings) and the subordinate ultraviolet (UV) triplet around 280 nm. These lines are of great diagnostic interest, as they encode information on the physical properties of the solar atmosphere from the upper photosphere to the chromosphere–corona transition region. We base our study on radiative transfer calculations of spectral line polarization in one-dimensional models of quiet and plage regions of the solar atmosphere. Our calculations take into account the combined action of atomic polarization, quantum level interference, frequency redistribution, and magnetic fields of arbitrary strength. In particular, we study the sensitivity of the emergent Stokes profiles to changes in the magnetic field through the Zeeman and Hanle effects. We also study the impact of the chromospheric plasma dynamics on the emergent Stokes profiles, taking into account the angle-dependent frequency redistribution in the h–k resonance transitions. The results presented here are of interest for the interpretation of spectropolarimetric observations in this important region of the solar UV spectrum.

The transfer of polarized radiation in resonance lines with partial frequency redistribution, J-state interference, and arbitrary magnetic fields. A radiative transfer code and useful approximations

“…Following the theoretical predictions summarized in the above-mentioned review paper, the intensity and polarization profiles of the H i Lymanα and Mg ii h & k lines were observed by the Chromospheric Lyman Alpha SpectroPolarimater (CLASP) and the Chromospheric Layer SpectroPolarimeter (CLASP2) sounding rocket experiments, respectively. Among a number of valuable findings (see Kano et al 2017;Trujillo Bueno et al 2018;Ishikawa et al 2021), they provided observational confirmation that both the H i Lyman-α and the Mg ii k lines present broad scattering polarization wing signals of large amplitude, in agreement with theoretical predictions (see Alsina Ballester et al 2016;del Pino Alemán et al 2016, 2020.…”

“…The scattering polarization profiles of strong resonance lines often show broad lobes that extend far beyond the Doppler core, thus allowing to probe the conditions in deeper layers of the solar at-mosphere. Interestingly, via the so-called magneto-optical (MO) effects, these wing signals are sensitive to the presence of longitudinal magnetic fields with strengths comparable to those that characterize the onset of the Hanle effect (Alsina Ballester et al 2016Ballester et al , 2019del Pino Alemán et al 2016, 2020.…”

Mapping Solar Magnetic Fields from the Photosphere to the Base of the Corona

“…We illustrate this in Figure S6 the response function of V /I to magnetic field perturbations in semi-empirical models of the solar atmosphere (38). The just quoted paper, which explains how the calculations of Figure S6 were done, shows also that in a plage model the response function of the external lobes peaks closer to the upper chromosphere than in a quiet Sun model.…”

Measuring the magnetic origins of solar flares, CMEs and Space Weather

“…Here, we extend this work with a larger grid of LOS angles and magnetic field strengths (see Figure 6 for the geometry) and show polarization amplitude and magnetic response "heat maps" in Figure 7. As in del Pino Alemán et al (2020) we used HanleRT to compute the intensity and polarization from a Mg II 3-term atom including PRD effects in atmosphere C of Fontenla et al (1993). We computed profiles for a grid of uniform magnetic field vectors inclined at θ B = −30 • from vertical, with fixed azimuth, and with |B| ranging from 1 to 200 G at 1 G intervals.…”