Imaging-polarimetric properties of the white-light inner corona during the 2017 total solar eclipse

Abstract

ABSTRACT We carried out the polarimetric observation of the white-light inner corona during the 2017 total solar eclipse in the United States. Degree of linear polarization (DLP) of the inner corona is obtained by the modulated polarized data. The electron density is inferred from the normalized white-light polarization brightness data. According to the observational results, we find that: (1) The DLP of the white-light corona increases with the height, peaking at approximately $1.3 \sim 1.35\, {\rm R}_{\odot }$ and then slightly decreases. In the coronal streamer region, DLP peaks at approximately 1.35 R⊙ and its value is about 40  per cent, whereas in the coronal hole region, DLP peaks at approximately 1.3 R⊙ and its value is about 35  per cent. (2) The azimuth angle of polarization sin (2χ) is symmetrical around the solar disk center. It can be easily found that the gradients of the angle of polarization, representing the direction of oscillations of the electric vector E, are tangential. Above the active region, the DLP distribution changes significantly, whereas the azimuth distribution is stable. This proves that the polarization of white-light corona is mainly caused by scattering polarization. (3) The electron density and the K-corona have similar distributions of properties. Electron density decreases from 6 × 107cm−3 to 2 × 106cm−3, whereas the height increases from $1.1\, {\rm R}_{\odot }$ to $1.85\, {\rm R}_{\odot }$. (4) An interesting finding is that, in the cavity region, there may be other polarization-induced mechanisms besides scattering, which can affect the value of the white-light DLP.