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

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-induced transition (MIT) theory. To verify the suitability of this method, we performed forward modeling with 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 Å 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 Å 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 Å 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 evaluated the impact of the uncertainty in the Fe x 3p 4 3d 4 D 5/2 and 4 D 7/2 energy difference on the magnetic field measurements.