Dark Halos around Solar Active Regions. I. Emission properties of the Dark Halo around NOAA 12706

Serena Maria Lezzi, Vincenzo Andretta, Mariarita Murabito +1

Dark areas around active regions (ARs) have been first observed in chromospheric lines more than a century ago and are now associated to the Hα fibril vortex around ARs. Nowadays,…