Forward Modeling of Magnetic-field Measurements at the Bases of Stellar Coronae through Extreme-Ultraviolet Spectroscopy

TL;DR

This paper develops a forward modeling approach to measure stellar coronal magnetic fields using extreme-ultraviolet spectroscopy and the magnetic-field-induced-transition (MIT) technique, demonstrating its applicability and limitations.

Contribution

It introduces a new method combining MHD models and MIT diagnostics to measure stellar magnetic fields from EUV spectra, expanding the potential for stellar magnetic studies.

Findings

The MIT technique can detect magnetic fields over three times solar maximum.

A signal-to-noise ratio of ~50 is needed for effective magnetic field measurements.

The method's applicability depends on the star's magnetic field strength and spectral quality.

Abstract

Measurements of the stellar coronal magnetic field are of great importance in understanding the stellar magnetic activity, yet the measurements have been extremely difficult. Recent studies proposed a new method of magnetic field measurements based on the magnetic-field-induced-transition (MIT) of the Fe~{\sc{x}} ion. Here we construct a series of stellar coronal magnetohydrodynamics (MHD) models and synthesize several Fe~{\sc{x}} emission lines at extreme-ultraviolet wavelengths, and then diagnose the magnetic field strength at the bases of the coronae using the MIT technique. Our results show that the technique can be applied to some stars with magnetic fields more than three times higher than that of the Sun at solar maximum. Furthermore, we investigate the uncertainty of the derived magnetic field strength caused by photon counting error and find that a signal-noise ratio of $\sim$50 for the Fe~{\sc{x}} 175 {\AA}~line is required to achieve effective measurements of the stellar coronal magnetic field.