Magnetic field diagnostics of prominences with the Mg II k line: 3D Stokes inversions versus traditional methods

TL;DR

This study compares 3D radiative transfer-based inversions with traditional methods for diagnosing magnetic fields in solar prominences using the Mg II k line, highlighting the advantages and limitations of each approach.

Contribution

It demonstrates that 3D radiative transfer inversions are essential for accurate magnetic field vector determination, while traditional methods can still provide useful insights in specific cases.

Findings

3D inversion methods are necessary for accurate magnetic field vector retrieval.

Traditional methods like weak field approximation can be useful under certain conditions.

Full geometric fidelity of the magnetic field cannot be achieved with current models.

Abstract

The Mg II k resonance line is commonly used for diagnosing the solar chromosphere. We theoretically investigated its intensity and polarization in solar prominences, taking 3D radiative transfer and Hanle and Zeeman effects into account. We used an optically thick 3D model representative of a solar prominence and applied several inversion methods to the synthetic Stokes profiles, clarifying their pros and cons for inferring prominence magnetic fields. We conclude that the self-consistent 3D inversion with radiative transfer is necessary to determine the magnetic field vector, although its geometry cannot be inferred with full fidelity. We also demonstrate that more traditional methods, such as those based on the weak field approximation or the constant-property slab assumption, can offer useful information under certain conditions.