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

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. We apply Milne-Eddington inversions on full Stokes vectors of the photospheric Si I 1082.7nm and the upper chromospheric He I triplet at 1083.0nm to obtain the magnetic field vector and velocity maps in two atmosphere layers. We find that (1) a complete filament was already present in Hα 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 600-800G in the upper chromosphere and 800-1000G 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. (4) In the chromosphere, consistent upflows are found along the PIL flanked by downflows. (5) The transversal magnetic field is nearly parallel to the PIL in the photosphere and inclined by 20°-30° in the chromosphere. (6) 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.