Do Hα Stokes V Profiles Probe the Chromospheric Magnetic Field? An Observational Perspective

Abstract

We investigated the diagnostic potential of the Stokes V profile of the H α line to probe the chromospheric line-of-sight (LOS) magnetic field ( B _LOS ) by comparing the B _LOS inferred from the weak field approximation (WFA) with that inferred from the multiline inversions of the Ca ii 8542 Å, Si i 8536 Å, and Fe i 8538 Å lines using the STiC inversion code. Simultaneous spectropolarimetric observations of a pore in the Ca ii 8542 Å and H α spectral lines obtained from the SPINOR at the Dunn Solar Telescope on 2008 December 4 are used in this study. The WFA was applied on the Stokes I and V profiles of H α line over three wavelength ranges, viz., around line core (Δ λ = ±0.35 Å), line wings (Δ λ = [−1.5, −0.6], and [+0.6, +1.5] Å), and full spectral range of the line (Δ λ = ± 1.5 Å) to derive the B _LOS . We found the maximum B _LOS strengths of ∼+800 and ∼+600 G at $\mathrm{log}{\tau }_{500}$ = −1 and −4.5, respectively, in the pore. The morphological map of the B _LOS inferred from the H α line core is similar to the B _LOS map at $\mathrm{log}{\tau }_{500}$ = −4.5 inferred from multiline inversions. The B _LOS map inferred from the H α line wings and full spectral range have a similar morphological structure to the B _LOS map inferred at $\mathrm{log}{\tau }_{500}$ = −1. The B _LOS estimated from H α using WFA is weaker by a factor of ≈0.53 than that of inferred from the multiline inversions.

Keywords

• Spectropolarimetry
• Radiative transfer
• Solar chromosphere
• Solar magnetic fields