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- Title
Coronal Photopolarimetry with the LASCO-C2 Coronagraph over 24 Years [1996 – 2019]: Application to the K/F Separation and to the Determination of the Electron Density.
- Authors
Lamy, Philippe; Llebaria, Antoine; Boclet, Brice; Gilardy, Hugo; Burtin, Michael; Floyd, Olivier
- Abstract
We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectrometric COronagraph/LASCO-C2 onboard the Solar and Heliospheric Observatory (SOHO). The polarimetric analysis of the white-light images makes use of polarized sequences composed of three images obtained though three polarizers oriented at + 60 ∘ , 0 ∘ , and − 60 ∘ , complemented by a neighboring unpolarized image, and relies on the formalism of Mueller. The Mueller matrix characterizing the C2 instrument was obtained through extensive ground-based calibrations of the optical components and global laboratory tests. Additional critical corrections were derived from in-flight tests relying prominently on roll sequences of SOHO, on the basis of consistency criteria (e.g. the "tangential" direction of polarization), and from several applications, notably the time-dependent tomographic reconstruction of the coronal electron density. This took several years of effort, but resulted in the quasi-uninterrupted photopolarimetric analysis of the corona over two complete Solar Cycles 23 and 24, and the comparison with a variety of eclipse data obtained at different phases of these cycles. Our final results encompass the characterization of the polarization of the white-light corona, of its polarized radiance, of the two-dimensional electron density, and of the K-corona. The agreement with the eclipse data is excellent except for slight discrepancies affecting the innermost part of the C2 field of view. The present work leaves the two unpolarized components, F-corona and stray light, entangled and their complex separation will be dealt with in a follow-on article.
- Subjects
ELECTRON density; SOLAR cycle; SOLAR corona; MUELLER calculus; IMAGE analysis; RADIANCE
- Publication
Solar Physics, 2020, Vol 295, Issue 7, pN.PAG
- ISSN
0038-0938
- Publication type
Article
- DOI
10.1007/s11207-020-01650-y