Measurements of the magnetic field strengths at the bases of stellar coronae using the magnetic-field-induced transition theory

TL;DR

This study explores using magnetic-field-induced transition theory to measure magnetic fields in stellar coronae, extending solar methods to other stars with stronger magnetic activity through modeling and spectral analysis.

Contribution

It demonstrates the feasibility of applying MIT-based spectral diagnostics to estimate magnetic fields in stellar coronae beyond the Sun, requiring specific ultraviolet spectrometry.

Findings

Method can measure magnetic fields in stars with higher surface flux than the Sun.

Spectral line ratios effectively estimate coronal magnetic field strengths.

Routine measurements need an extreme ultraviolet spectrometer.

Abstract

Measurements of the magnetic field in the stellar coronae are extremely difficult. Recently, it was proposed that the magnetic-field-induced transition (MIT) of the Fe X 257 {\AA} line can be used to measure the coronal magnetic field of the Sun. We performed forward modeling with a series of global stellar magnetohydrodynamics models to investigate the possibility of extending this method to other late-type stars. We first synthesized the emissions of several Fe X lines for each stellar model, then calculated the magnetic field strengths using the intensity ratios of Fe X 257 {\AA} to several other Fe X lines based on the MIT theory. Finally, we compared the derived field strengths with those in the models, and concluded that this method can be used to measure at least the magnetic field strengths at the coronal bases of stars with a mean surface magnetic flux density about one order of magnitude higher than that of the Sun. Our investigation suggests the need of an extreme ultraviolet spectrometer to perform routine measurements of the stellar coronal magnetic field.