Spectropolarimetric analysis of an active region filament

I. Magnetic and dynamical properties from single component inversions

¹ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
e-mail: carlos.diaz@astro.su.se
² Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
³ Institute for Solar Physics, Dept. of Astronomy, Stockholm University, AlbaNova University Centre, 10691 Stockholm, Sweden

Received: 6 December 2018
Accepted: 12 April 2019

Abstract

Aims. The determination of the magnetic filed vector in solar filaments is made possible by interpreting the Hanle and Zeeman effects in suitable chromospheric spectral lines like those of the He I multiplet at 10 830 Å. We study the vector magnetic field of an active region filament (NOAA 12087).

Methods. Spectropolarimetric data of this active region was acquired with the GRIS instrument at the GREGOR telescope and studied simultaneously in the chromosphere with the He I 10 830 Å multiplet and in the photosphere Si I 10 827 Å line. As has been done in previous studies, only a single-component model was used to infer the magnetic properties of the filament. The results are put into a solar context with the help of the Solar Dynamic Observatory images.

Results. Some results clearly point out that a more complex inversion had to be performed. First, the Stokes V map of He I does not show a clear signature of the presence of the filament. Second, the local azimuth map follows the same pattern as Stokes V; it appears that polarity of Stokes V is conditioning the inference to very different magnetic fields even with similar linear polarization signals. This indication suggests that the Stokes V could be dominated from below by the magnetic field coming from the active region, and not from the filament itself. This evidence, and others, will be analyzed in depth and a more complex inversion will be attempted in the second part of this series.