Derived Electron Densities from Linear Polarization Observations of the Visible-Light Corona During the 14 December 2020 Total Solar Eclipse

• DOI: 10.1007/s11207-023-02231-5
• Publication Date: 2023-12-05T17:02:01Z
• Authors: Liam Edwards; Kaine A. Bunting; Brad Ramsey; Matthew Gunn; Tomos Fearn; Thomas Knight; Gabriel Domingo Muro; Huw Morgan
• Keywords: Astrophysics - Solar and Stellar Astrophysics; 0103 physical sciences; FOS: Physical sciences; 01 natural sciences; Solar and Stellar Astrophysics (astro-ph.SR)

AbstractA new instrument was designed to take visible-light (VL) polarized brightness ($\mathit{pB}$ pB ) observations of the solar corona during the 14 December 2020 total solar eclipse. The instrument, called the Coronal Imaging Polarizer (CIP), consisted of a 16 MP CMOS detector, a linear polarizer housed within a piezoelectric rotation mount, and an f-5.6, 200 mm DSLR lens. Observations were successfully obtained, despite poor weather conditions, for five different exposure times (0.001 s, 0.01 s, 0.1 s, 1 s, and 3 s) at six different orientation angles of the linear polarizer ($0^{\circ}$

0 ∘

, $30^{\circ}$

30 ∘

, $60^{\circ}$

60 ∘

, $90^{\circ}$

90 ∘

, $120^{\circ}$

120 ∘

, and $150^{\circ}$

150 ∘

). The images were manually aligned using the drift of background stars in the sky and images of different exposure times were combined using a simple signal-to-noise ratio cut. The polarization and brightness of the local sky were also estimated and the observations were subsequently corrected. The $\mathit{pB}$ pB of the K-corona was determined using least-squares fitting and radiometric calibration was done relative to the Mauna Loa Solar Observatory (MLSO) K-Cor $\mathit{pB}$ pB observations from the day of the eclipse. The $\mathit{pB}$ pB data was then inverted to acquire the coronal electron density, $n_{e}$

n e

, for an equatorial streamer and a polar coronal hole, which agreed very well with previous studies. The effect of changing the number of polarizer angles used to compute the $\mathit{pB}$ pB is also discussed and it is found that the results vary by up to $\approx 13\%$ ≈ 13 % when using all six polarizer angles versus only a select of three angles.