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

The Mg II k resonance line is commonly used for diagnosing the solar chromosphere. Here we theoretically investigate its intensity and polarization in solar prominences, taking into account the effects of 3D radiative transfer and the Hanle and Zeeman effects. We use an optically thick 3D model representative of a solar prominence and apply 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.