Polarization of the Corona Observed During the 2017 and 2019 Total Solar Eclipses
Solar Science Observatory, NAOJ
The white-light solar corona consists of the K-corona from the million-degree plasma of the Sun and the F-corona from the interplanetary dust. Linear-polarization information enables the separation of the K- and F-corona. Therefore, polarimetry has long been performed in total eclipse observations as well as in coronagraph observations. Total solar eclipses provide us very low sky-background down to just above the solar limb, which cannot be achieved in coronagraph observations. Therefore, the white-light corona has been a particularly important target for the total solar eclipse observations.
We carried out polarimetric observations of the white-light corona during the total solar eclipses on 2017 August 21 and 2019 July 2 by taking advantage of professional-amateur collaborations, and successfully obtained data at two different sites for both eclipses. After eliminating sky-background, we obtained the brightness (BK+F) and polarization (pK+F) of the K+F corona, as presented in Figure 1 (polarization data are available here).
In Figure 2, comparison of the derived degree of polarization with other measurement results for the 2017 eclipse are presented. The eclipse data by Vorobiev et al. (2020, Pub. Astron. Soc. Pac. 132, 024202) (green lines), show good coincidence with ours. However, the results of the Large Angle Spectrometric Coronagraph (LASCO) C2 of the Solar and Heliospheric Observatory (LASCO C2 Legacy Archive, http://idoc-lasco.ias.u-psud.fr/sitools/client-portal/doc/) (red lines) taken on the day of the eclipse are systematically smaller than ours and those by Vorobiev et al.
Because the pK+F represents the brightness of the K-corona, the discrepancy among the pK+F values leads an error in the estimation of the amount of hot plasma. However, well-calibrated eclipse data, which were taken with a wide field-of-view, enable intercomparison among various data and contribute to the correction of the systematic error in the results from other observations. The eclipse observations provide a standard to study the amount of the hot corona quantitatively.
Thus, derived correct amount of the hot plasma of the corona is important to study the coronal plasma-producing mechanism and the coronal variation according to the solar activity cycle.
These results appeared as Hanaoka, Y., Sakai, Y., and Takahashi, K. “Polarization of the Corona Observed During the 2017 and 2019 Total Solar Eclipses” in Solar Physics (2021, 296, 158; doi: 10.1007/s11207-021-01907-0).
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Fig. 1. Polarization map of the K+F corona covering 8.2 × 8.2 Rsun area obtained during the 2017 eclipse after the elimination of the sky background. The grayscale image represents the brightness of the K+F corona, and the degree and orientation of the linear polarization signals are depicted with orange ticks. The solar north is to the top. |
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Fig. 2. Comparison of the degree of polarization (pK+F) of the streamers around the equator (solid lines) and the poles (dashed lines) among the our eclipse observation (black), the results by Vorobiev et al. (green), and those from LASCO C2 observation (red). |
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