Magnetic fields of an active region filament from full Stokes analysis of Si I 1082.7 nm and He I 1083.0 nm

TL;DR

This study uses full Stokes spectro-polarimetric data to analyze the magnetic field structure of an active region filament across different atmospheric layers, revealing complex magnetic configurations and supporting flux rope emergence models.

Contribution

It provides a detailed multi-layer magnetic field analysis of an active region filament using Milne-Eddington inversions on Si I and He I lines, highlighting new insights into filament magnetic topology.

Findings

Presence of a complete filament in Hα and partial in He I.

Two magnetic field strength regimes in the filament.

Magnetic field configuration consistent with flux rope emergence.

Abstract

Vector magnetic fields of an active region filament in the photosphere and upper chromosphere are obtained from spectro-polarimetric observations recorded with the Tenerife Infrared Polarimeter (TIP II) at the German Vacuum Tower Telescope (VTT). We apply Milne-Eddington inversions on full Stokes vectors of the photospheric Si I 1082.7 nm and the upper chromospheric He I triplet at 1083.0 nm to obtain magnetic field vector and velocity maps in two atmosphere layers. We find that: (1)A complete filament was already present in H$\alpha$ at the beginning of the TIP II data acquisition. Only a partially formed one, composed of multiple small threads, was present in He I. (2) The AR filament comprises two sections. One shows strong magnetic field intensities, about 600 - 800 G in the upper chromosphere and 800 - 1000 G in the photosphere. The other exhibits only comparatively weak magnetic field strengths in both layers. (3) The Stokes V signal is indicative of a dip in the magnetic field strength close to the chromospheric PIL. (3) In the chromosphere consistent upflows are found along the PIL flanked by downflows. (4) The transversal magnetic field is nearly parallel to the PIL in the photosphere and inclined by 20 - 30 degree in the chromosphere. (5) The chromospheric magnetic field around the filament is found to be in normal configuration, while the photospheric field presents a concave magnetic topology. The observations are consistent with the emergence of a flux rope with a subsequent formation of a filament.