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Solar Physics

, 294:12 | Cite as

Dependence of DOLP on Coronal Electron Temperature, Speed, and Structure

  • Nelson ReginaldEmail author
  • Lutz Rastaetter
Article

Abstract

The degree of linear polarization (DOLP) is an important measure of the fraction of the total K-coronal brightness due to Thomson scattering of photospheric brightness off the coronal electrons that is linearly polarized. However, the corona is also brightened by the F-coronal brightness due to scattering of photospheric brightness off everything else in the corona except the electrons, which remains totally unpolarized at least up to a coronal height of \(\approx 5~\mathrm{R}_{ \odot }\). As a result, to measure the DOLP, the F- and K-coronal brightness need to be separated by taking three consecutive images by turning a linear polarizer through three well-defined angles or with a single image using a polarization camera. In this regard, the theoretically computed DOLP would be a helpful tool to compare with the experimentally measured DOLP on the real corona in order to estimate how well the F-coronal brightness is removed from the total coronal brightness to isolate the K-coronal brightness. This is important because the K-coronal brightness ratios at (410.3 nm/390.0 nm) and (423.3 nm/398.7 nm) can be used to generate maps of electron temperature and speed, respectively, and the individual K-coronal brightness at all four wavelengths can be used independently to generate maps of the electron density in the corona. In this article, for a spherically symmetric model (SSM) corona with assumed temperatures of 1.0 MK and 2.0 MK and radial flow speeds of 0.0 km s−1 and 250.0 km s−1 for the coronal electrons, we have computed the wavelength-dependent DOLP from 370.0 nm to 470.0 nm in intervals of 1.0 nm, and for a spherically asymmetric model (SAM) corona containing a simulation of the Bastille Day coronal mass ejection, streamers, and quiet areas, we have generated maps of DOLP at the four wavelengths 390.0, 398.7, 410.3, and 423.3 nm. Finally, we have used these theoretically computed models of DOLP to compare with the experimentally measured DOLP.

Keywords

K corona F corona Electron temperature Electron speed Electron density DYN method Degree of linear polarization (DOLP) 

Notes

Acknowledgements

The authors of this manuscript are thankful to Joseph Lemaire and Koen Stegen, the authors of the article (Lemaire and Stegen 2016), for actively participating in the investigation on how and why the K-coronal brightness spectra produced by both the DYN and uniform methods have the same shapes and magnitudes. In this regard, they shared with us the software codes developed by them at BIRA-IASB, Belgium, to compute the DYN temperature profiles. This joint effort on test/verification lead to the important material presented in the Appendix to this manuscript; specifically, Figure 13 was produced under suggestion by Joseph Lemaire. Additionally, Jospeh Lemaire’s suggestions on the introduction, the idea to incorporate the progression of the K-coronal models from the earlier days to the present for the benefit of the Solar Physics readership, suggestions for the formats of the figures and identifying numerous other errors in the text that were missed by the authors helped in greatly improving the final version of this manuscript. We also thank Predictive Science Inc. for sharing with us their Bastille Day CME model. N.L.R. was supported by NASA grant PL10A-125.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.The Catholic University of America at NASA’s Goddard Space Flight CenterGreenbeltUSA
  2. 2.NASA’s Goddard Space Flight CenterGreenbeltUSA

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