Filigree in the Surroundings of Polar Crown and High-Latitude Filaments

TL;DR

This study provides high-resolution observations of polar crown and high-latitude filaments, revealing the properties and evolution of bright points near these filaments and their relation to magnetic concentrations and filament decay.

Contribution

It offers the first detailed analysis of bright points near polar crown filaments, linking their morphology and magnetic context to filament evolution.

Findings

Bright points near polar filaments are larger and similar in shape to those at lower latitudes.

Bright points are associated with stronger magnetic flux concentrations at filament footpoints.

The number of bright points increases as the filament decays, affecting filament stability.

Abstract

High-resolution observations of polar crown and high-latitude filaments are scarce. We present a unique sample of such filaments observed in high-resolution H$\alpha$ narrow-band filtergrams and broad-band images, which were obtained with a new fast camera system at the Vacuum Tower Telescope (VTT), Tenerife, Spain. The Chromospheric Telescope (ChroTel) provided full-disk context observations in H$\alpha$, Ca II K, and He I 10830 A. The Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) provided line-of-sight magnetograms and ultraviolet (UV) 1700 A filtergrams, respectively. We study filigree in the vicinity of polar crown and high-latitude filaments and relate their locations to magnetic concentrations at the filaments' footpoints. Bright points are a well studied phenomenon in the photosphere at low latitudes, but they were not yet studied in the quiet network close to the poles. We examine size, area, and eccentricity of bright points and find that their morphology is very similar to their counterparts at lower latitudes, but their sizes and areas are larger. Bright points at the footpoints of polar crown filaments are preferentially located at stronger magnetic flux concentrations, which are related to bright regions at the border of supergranules as observed in UV filtergrams. Examining the evolution of bright points on three consecutive days reveals that their amount increases while the filament decays, which indicates they impact the equilibrium of the cool plasma contained in filaments.