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

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.

arXiv commentProceedings 12th Potsdam Thinkshop to appear in Astronomische Nachrichten

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Cited by in corpus (11)

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• Temporal evolution of arch filaments as seen in He I 10830 Å
• The problem of the height dependence of magnetic fields in sunspots
• High-resolution imaging and near-infrared spectroscopy of penumbral decay
• Height variation of magnetic field and plasma flows in isolated bright points
• Magnetized supersonic downflows in the chromosphere. A statistical study using the He I 10830 Å lines
• On the effect of oscillatory phenomena on Stokes inversion results
• Tracking downflows from the chromosphere to the photosphere in a solar arch filament system
• The dynamics of AR 12700 in its early emerging phase II: fan-shaped activities relevant to arch filament systems
• Dynamics and connectivity of an extended arch filament system
• An Unusual Velocity Field in a Sunspot Penumbra