The Color and Brightness of the F-corona Inferred from the 2019 July 2 Total Solar Eclipse

Abstract

Total solar eclipses (TSEs) provide a unique opportunity to quantify the properties of the K-corona (electrons), F-corona (dust), and E-corona (ions) continuously from the solar surface out to a few solar radii. We apply a novel inversion method to separate emission from the K- and F-corona continua using unpolarized total brightness (tB) observations from five 0.5 nm bandpasses acquired during the 2019 July 2 TSE between 529.5 and 788.4 nm. The wavelength dependence relative to the photosphere (i.e., color) of the F-corona itself is used to infer the tB of the K- and F-corona for each line of sight. We compare our K-corona emission results with the Mauna Loa Solar Observatory (MLSO) K-Cor polarized brightness (pB) observations from the day of the eclipse, and the forward modeled K-corona intensity from the Predictive Science Inc. (PSI) magnetohydrodynamic (MHD) model prediction. Our results are generally consistent with previous work and match both the MLSO data and PSI-MHD predictions quite well, supporting the validity of our approach and of the PSI-MHD model. However, we find that the tB of the F-corona is higher than expected in the low corona, perhaps indicating that the F-corona is slightly polarized—challenging the common assumption that the F-corona is entirely unpolarized.

Integral Field Spectroscopy with the Solar Gravitational Lens

“…Most of these measurements are taken with visible light wavelengths, although some effort has been made to make measurements in the near-infrared as well, and the results are compiled into Figures 5 in Boe et al (2021) and Figure 2 in Kimura & Mann (1998). In Figure 2 of Kimura & Mann (1998), the scatter is large; there is a slight increase at longer wavelengths, going from roughly 10 −9 B e at λ = 0.3 μm to 10 −8 B e at λ = 3 μm for elongations of ò = 4R e .…”

“…in Mann (1992), Figure1inKimura & Mann (1998), Figure1inHoward et al (2019), and Figure9inBoe et al (2021), we are able to analyze the solar coronal brightness across a wide range of elongations ò. The data are reproduced in Figure17(a) for convenience.…”

Integral field spectroscopy with the solar gravitational lens

“…The resulting power law curve is shown in black in Figure (17 a). Most of these measurements are taken with visible light wavelengths, although some effort has been made to make measurements in the near-infrared as well, and the results are compiled into Figures (5) in (Boe et al 2021) and ( 2) in (Kimura & Mann 1998). In Figure ( 2) of (Kimura & Mann 1998), the scatter is large, there is a slight increase at longer wavelengths, going from roughly 10 −9 B at λ = 0.3µm to 10 −8 B at λ = 3µm for elongations of = 4R .…”

“…In Figure ( 2) of (Kimura & Mann 1998), the scatter is large, there is a slight increase at longer wavelengths, going from roughly 10 −9 B at λ = 0.3µm to 10 −8 B at λ = 3µm for elongations of = 4R . Figure ( 5) of (Boe et al 2021) reports relative intensities over λ ∈ [0.5, 0.8]µm, and measures a spectral power law index of B corona ∝ λ 0.91±0.07 . This reddening effect could be the result of thermal emission from the particles themselves, as well as preferential directional scattering of thermal emission from the sun.…”

The Double-Bubble CME of the 2020 December 14 Total Solar Eclipse

“…Ground-based coronagraphs cover the lower corona, but they are limited by atmospheric scattering to a maximum of ∼1.3 R (Boe et al 2021). On the other hand, space-based coronagraphs are only able to probe the outer region of the corona beyond ∼2.2 R due to diffraction of photospheric light at the edge of the occulter.…”