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EP: Fachverband Extraterrestrische Physik
EP 11: Sun and Heliosphere IV
EP 11.1: Vortrag
Donnerstag, 3. April 2025, 13:45–14:00, ZHG101
Magnetic structure of coronal dark halos — •Jonathan Nölke1, Johann Hirzberger1, Hardi Peter1,2, Sami Solanki1, and Pradeep Chitta1 — 1Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany — 2Institut für Sonnenphysik (KIS), Freiburg, Germany
At low temperatures around 1 MK, distinct regions of the solar corona exhibit emission levels significantly below those of the quiet Sun. A prominent example are dark halos surrounding active regions, which are sometimes misidentified as coronal holes (CH). While the well-studied CHs owe their darker appearance to open magnetic field lines, the formation mechanism of dark halos remains unclear.
On 5 November 2021, Solar Orbiter and the Solar Dynamics Observatory observed the dark halo surrounding active region NOAA 12893. One of its patches overlaps with an adjacent CH, providing a unique opportunity to directly compare the two phenomena.
The magnetic field underneath the dark halo is weaker than in brighter areas. At its outer boundaries, it shows even lower field strengths than those typically found in the quiet Sun. In contrast to the reduced coronal emission at temperatures around 1 MK, at higher temperatures the emission is stronger. This shows a clear difference to CHs, which characteristically exhibit reduced emission at these temperatures. We further demonstrated that unlike the embedded CH, the dark halo patches are magnetically closed.
Our combined EUV and magnetic field observations suggest that dark halos result from reduced heating.
Keywords: Sun; Magnetic fields; Corona; Photosphere; Active region