Spectropolarimetric analysis of an active region filament. II. Evidence of the limitations of a single component model

TL;DR

This study reveals the limitations of single component models in analyzing the magnetic fields of active region filaments, demonstrating the need for more complex models to interpret spectropolarimetric data accurately.

Contribution

The paper provides evidence that single component models are insufficient for interpreting the magnetic field signatures in active region filaments, highlighting the necessity for multi-component approaches.

Findings

Single component models cannot explain all observed Stokes profiles.

Circular polarization signals indicate strong magnetic field gradients.

Absorption effects allow magnetic field detection below the filament.

Abstract

Our aim is to demonstrate the limitations of using a single component model to study the magnetic field of an active region filament. For that we have analyzed the polarimetric signals of the He I 10830 A multiplet acquired with the infrared spectrograph GRIS of the GREGOR telescope (Tenerife, Spain). After a first analysis of the general properties of the filament using Hazel under the assumption of a single component model atmosphere, in this second part we focus our attention on the observed Stokes profiles and the signatures which cannot be explained with this model. We have found an optically thick filament where the blue and the red components have the same sign in the linear polarization as an indication of radiative transfer effects. Moreover, the circular polarization signals inside the filament show the presence of strong magnetic field gradients. We have also shown that even a filament with such high absorption still shows signatures of the circular polarization generated by the magnetic field below the filament. The reason is that the absorption of the spectral line decays very quickly towards the wings, just where the circular polarization has a larger amplitude. In order to separate both contributions, we explore the possibility of a two component model but the inference becomes impossible to overcome as a high number of solutions is compatible with the observations.