Coronal Densities, Temperatures, and Abundances during the 2019 Total Solar Eclipse: The Role of Multiwavelength Observations in Coronal Plasma Characterization

Abstract

The Airborne Infrared Spectrometer (AIR-Spec) offers an unprecedented opportunity to explore the near-infrared (NIR) wavelength range. It has been flown at two total solar eclipses, in 2017 and 2019. The wavelength range of the much-improved instrument on the second flight (2019 July 2) was shifted to cover two density-sensitive lines from S xi. In this paper we study detailed diagnostics for temperature, electron density, and elemental abundances by comparing results from AIR-Spec slit positions above the east and west limbs with those from Hinode/EIS, the PolarCam detector, and SDO/AIA. We find very good agreement in the electron densities obtained from the EIS EUV line ratios, those from the NIR S xi ratio, and those obtained from the polarized brightness PolarCam measurements. Electron densities ranged from log N e [cm−3] = 8.4 near the limb to 7.2 at R 0 = 1.3. EIS spectra indicate that the temperature distribution above the west limb is near isothermal at around 1.3 MK, while that on the east has an additional higher-T component. The AIR-Spec radiances in Si x and S xi, as well as the AIA data in the 171, 193, and 211 Å bands, are consistent with the EIS results. EIS and AIR-Spec data indicate that the sulfur abundance (relative to silicon) is photospheric in both regions, confirming our previous results of the 2017 eclipse. The AIA data also indicate that the absolute iron abundance is photospheric. Our analysis confirms the importance of the diagnostic potential of the NIR wavelength range and that this important wavelength range can be used reliably and independently to determine coronal plasma parameters.

Defining the Middle Corona

“…Also, an accurate knowledge of the local density is needed to calculate the relative contribution of the collisional-excitation and resonant photo-excitation processes. Obtaining densities from, e.g., line ratios of forbidden lines is not trivial: The plane-of-the-sky approximation is reasonable for the allowed transitions not affected by resonant photo-excitation, but the lines affected have a significant long-range contribution (see, e.g., Yang et al., 2020 ; Del Zanna et al., 2023 ). As a consequence, measurements of the ionization temperature from the resonant photo-excitation lines becomes strongly dependent on the distributions of the electron densities.…”

The Solar Minimum Eclipse of 2019 July 2. III. Inferring the Coronal T e with a Radiative Differential Emission Measure Inversion

“…Outside of EUV and X-ray DEM inversions, the coronal electron temperature has been inferred with emission-line ratios at wavelengths in the ultraviolet from space (e.g., Raymond et al 1997;Ko et al 2002) and in the visible and infrared during total solar eclipses (e.g., Boe et al 2020aBoe et al , 2022Del Zanna et al 2023). Without emission lines, the effective temperature has been inferred using the density profile inferred from polarized brightness measurements (e.g., Munro & Jackson 1977).…”