An active region filament studied simultaneously in the chromosphere and photosphere: I - Magnetic structure

TL;DR

This study provides a detailed multiwavelength analysis of an active region filament, revealing its magnetic structure, evolution, and the relationship between chromospheric and photospheric magnetic fields, suggesting a flux rope topology.

Contribution

It offers the first simultaneous multiheight magnetic field measurements of an AR filament, proposing an evolutionary scenario and linking orphan penumbrae to flux ropes in the photosphere.

Findings

Filament exhibits a flux rope magnetic topology.

Photospheric and chromospheric magnetic fields show different configurations.

Orphan penumbrae are linked to flux ropes in the photosphere.

Abstract

A thorough multiwavelength, multiheight study of the vector magnetic field in a compact active region (AR) filament (NOAA10781) is presented. We suggest an evolutionary scenario for this filament. Full Stokes vectors were acquired with TIP-II in a spectral range which comprises the chromospheric He I 10830 A multiplet and the photospheric Si I 10827 A line. An AR filament (that was formed before our observing run) was detected in the He I absorption images on 2005 July 3rd. The chromospheric vector magnetic field in this portion of the filament was strongly sheared whereas the photospheric field lines underneath had an inverse polarity configuration. From July 3rd to July 5th, an opening and closing of the polarities at either side of the polarity inversion line (PIL) was recorded, resembling the recently discovered process of the sliding door effect seen by Hinode. During this time, a newly created region that contained pores and orphan penumbrae at the PIL was observed.On July 5th, a normal polarity configuration was inferred from the chromospheric spectra, while strongly sheared field lines aligned with the PIL were found in the photosphere. In this same data set, the spine of the filament is also observed in a different portion of the FOV and is clearly mapped by the Silicon line core. The inferred vector magnetic fields of the filament suggest a flux rope topology. Furthermore, the observations indicate that the filament is divided in two parts, one which lies in the chromosphere and another one that stays trapped in the photosphere. Therefore, only the top of the helical structure is seen by the Helium lines. The pores and orphan penumbrae at the PIL appear to be the photospheric counterpart of the extremely low-lying filament. We suggest that orphan penumbrae are formed in very narrow PILs of compact ARs and are the photospheric manifestation of flux ropes in the photosphere.