First Metis Detection of the Helium D<SUB>3</SUB> Line Polarization in a Large Eruptive Prominence

Heinzel, Petr; Jejčič, Sonja; Štěpán, Jiří; Susino, Roberto; Andretta, Vincenzo; Russano, Giuliana; Fineschi, Silvano; Romoli, Marco; Bemporad, Alessandro; Berlicki, Arkadiusz; Burtovoi, Aleksandr; Da Deppo, Vania; De Leo, Yara; Grimani, Catia; Jerse, Giovanna; Landini, Federico; Naletto, Giampiero; Nicolini, Gianalfredo; Pancrazzi, Maurizio; del Pino Alemán, Tanausú; Sasso, Clementina; Spadaro, Daniele; Stangalini, Marco; Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela; Vicente Arévalo, Andrés
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The Astrophysical Journal

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Metis on board Solar Orbiter is the space coronagraph developed by an Italian-German-Czech consortium. It is capable of observing solar corona and various coronal structures in the visible-light (VL) and UV (hydrogen Lyα) channels simultaneously for the first time. Here we present observations of a large eruptive prominence on 2021 April 25-26, in the VL, taken during the mission cruise phase, and demonstrate that apart from the broadband continuum emission, which is due to the Thomson scattering on prominence electrons, we detect a significant radiation in the neutral-helium D3 line (587.6 nm), which lies within the Metis VL passband. We show how the prominence looks like in Stokes I, Q, and U. We consider two extreme cases of the prominence magnetic field, and we separate the Stokes I and Q signals pertinent to Thomson scattering and to the D3 line. The degree of linear polarization of the D3 line (both Q and U) indicates the presence of the prominence magnetic field; hence Metis can serve as a magnetograph for eruptive prominences located high in the corona.
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Magnetism, Polarization and Radiative Transfer in Astrophysics
Magnetic fields pervade all astrophysical plasmas and govern most of the variability in the Universe at intermediate time scales. They are present in stars across the whole Hertzsprung-Russell diagram, in galaxies, and even perhaps in the intergalactic medium. Polarized light provides the most reliable source of information at our disposal for the
Tanausú del
Pino Alemán