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CLARO: A Telescope to Observe Scattering Polarization in the UV Corona.

Presentation #121.03 in the session Observing and Inferring solar Chromospheric and Coronal Magnetic Fields — Poster Session.

Published onOct 20, 2022
CLARO: A Telescope to Observe Scattering Polarization in the UV Corona.

The structuring of coronal plasma by the magnetic field is the key to understanding the fundamental physical processes of energy build up, storage, and release throughout the solar corona. Measurements of the coronal magnetic field vector in the global corona are thus crucial to understanding and modeling coronal dynamics and space weather. Ground-based efforts are largely limited to the observation of forbidden emission lines in the low corona. They also require large telescopes to reveal the small polarization signatures of the Zeeman effect produced by the weak coronal field. A complementary, and largely unexplored diagnostic of the coronal magnetic field vector is offered by the linear polarization signature of the Hanle effect of far ultraviolet (FUV) resonance lines. In particular, H I Lyman-alpha offers an almost unique opportunity for a comprehensive view of the solar corona and its structuring by the magnetic field. This line’s scattering polarization is sensitive to fields between a few gauss to about 100 gauss, allowing the direct measurement of closed fields above active regions and in coronal prominence cavities and arcades. At larger coronal heights and in coronal regions dominated by weaker open fields, the Lyman-alpha polarization is instead practically insensitive to the magnetic field, and it becomes a proxy for diagnosing solar wind outflows and plasma temperature anisotropies. The strong linear polarization signal produced by resonance scattering in the FUV coronal lines, and its sensitivity to the magnetic field strength and topology via the Hanle effect, make these diagnostics accessible to modest aperture (10-30 cm) telescopes, e.g., the Coronal Lyman-α Resonance Observatory (CLARO).


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