Forward Modeling of Solar Coronal Magnetic Field Measurements Based on a Magnetic-field-induced Transition in Fe X

TL;DR

This study validates a novel method using Fe X spectral line ratios and magnetic-field-induced transition theory to measure the solar coronal magnetic field, supported by forward modeling with a 3D MHD model.

Contribution

The paper demonstrates the feasibility of using Fe X line ratios and MIT theory for coronal magnetic field measurement through forward modeling and introduces a new method for estimating coronal density and temperature.

Findings

MIT technique provides reasonably accurate magnetic field measurements.

A spectrometer observing multiple Fe X lines is essential for reliable results.

Uncertainty in Fe X energy levels impacts magnetic field estimates.

Abstract

It was recently proposed that the intensity ratios of several extreme ultraviolet spectral lines from the Fe X ion can be used to measure the solar coronal magnetic field based on the magnetic-field-inducedtransition (MIT) theory. To verify the suitability of this method, we performed forward modelingwith a three-dimensional radiation magnetohydrodynamic model of a solar active region. Intensities of several spectral lines from Fe X were synthesized from the model. Based on the MIT theory, intensity ratios of the MIT line Fe X 257 A to several other Fe X lines were used to derive the magnetic field strengths, which were then compared with the field strengths in the model. We also developed a new method to simultaneously estimate the coronal density and temperature from the Fe X 174/175 and 184/345 A line ratios. Using these estimates, we demonstrated that the MIT technique can provide reasonably accurate measurements of the coronal magnetic field in both on-disk and off-limb solar observations. Our investigation suggests that a spectrometer that can simultaneously observe the Fe X 174, 175, 184, 257, and 345 A lines and allow an accurate radiometric calibration for these lines is highly desired to achieve reliable measurements of the coronal magnetic field. We have also evaluatedthe impact of the uncertainty in the Fe X 3p4 3d 4D5/2 and 4D7/2 energy difference on the magnetic field measurements.