Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope

TL;DR

This study uses the GREGOR solar telescope to analyze the magnetic and velocity structures of an arch filament system in the sun's atmosphere, revealing details about flux emergence and plasma flows.

Contribution

First spectropolarimetric observations of an arch filament system with the GREGOR telescope, providing new insights into magnetic field configurations and plasma dynamics.

Findings

Fibrils connect sunspots with opposite magnetic polarity patches.

Chromospheric downflows reach up to 30 km/s.

Results support models of emerging flux with downward plasma flows.

Abstract

Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines Si I 1082.7 nm, He I 1083.0 nm, and Ca I 1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the arch filament system connect the sunspot with patches of magnetic polarity opposite to that of the spot. These patches do not necessarily coincide with pores, where the magnetic field is strongest. Instead, areas are preferred not far from the polarity inversion line. These areas exhibit photospheric downflows of moderate velocity, but significantly higher downflows of up to 30 km/s in the chromospheric helium line. Our findings can be explained with new emerging flux where the matter flows downward along the fieldlines of rising flux tubes, in agreement with earlier results.