New deep coronal spectra from the 2017 total solar eclipse

Abstract

Context. The origin of the high temperature of the solar corona, in both the inner bright parts and the more outer parts showing flows toward the solar wind, is not understood well yet. Total eclipses permit a deep analysis of both the inner and the outer parts of the corona using the continuum white-light (W-L) radiations from electrons (K-corona), the superposed spectrum of forbidden emission lines from ions (E-corona), and the dust component with F-lines (F-corona). Aims. By sufficiently dispersing the W-L spectrum, the Fraunhofer (F) spectrum of the dust component of the corona appears and the continuum Thomson radiation can be evaluated. The superposed emission lines of ions with different degrees of ionization are studied to allow the measurement of temperatures, non-thermal velocities, Doppler shifts, and abundances to constrain the proposed heating mechanisms and understand the origin of flows that lead to solar wind. Methods. We describe a slit spectroscopic experiment of high spectral resolution to provide an analysis of the most typical parts of the quasi-minimum type corona observed during the total solar eclipse of Aug 21, 2017 from Idaho, USA. Streamers, active region enhancements, and polar coronal holes (CHs) are measured well using deep spectra. Results. Sixty spectra are obtained during the totality with a long slit, covering ±3 solar radii in the range of 510 nm to 590 nm. The K+F continuum corona is exposed well up to two solar radii. The F-corona can be measured even at the solar limb. New weak emission lines were discovered or confirmed. The rarely observed Ar X line is detected almost everywhere; the Fe XIV and Ni XIII lines are clearly detected everywhere. For the first time hot lines are also measured inside the CH regions. The radial variations of the non-thermal turbulent velocities of the lines do not show a great departure from the average values. No significantly large Doppler shifts are seen anywhere in the inner or the middle corona. The wings of the Fe XIV line show some non-Gaussianity. Conclusions. Deep slit coronal spectra offered an opportunity for diagnosing several aspects of coronal physics during a well observed total eclipse without extended investments. The analysis of the ionic emission line profiles offers several powerful diagnostics of the coronal dynamics; the precise measurement of the F-continuum component provides insight into the ubiquitous dust corona at the solar limb.1

The Solar Minimum Eclipse of 2019 July 2. II. The First Absolute Brightness Measurements and MHD Model Predictions of Fe x, xi, and xiv out to 3.4 R ⊙

“…The observed emission was typically limited to a helioprojective distance less than 1.4 R e , though occasionally emission was recorded up to 1.7 R e (Singh et al 1982). Recent work has continued to employ line emission observed during TSEs as a means to study the physical properties of the solar corona, including the ionic freeze-in distances (Habbal et al 2007(Habbal et al , 2013Boe et al 2018), the average electron temperature (T e ; Boe et al 2020a), the sources of the solar wind in the corona (Habbal et al 2021), and the presence of various ionic species with slit spectrographs (Ding & Habbal 2017;Samra et al 2018;Koutchmy et al 2019).…”

Complexity of the Upper Solar Atmosphere Revealed from Spectropolarimetry during a Solar Eclipse

“…One clue for the judgment of the combination of polarization sources under subresolution can be found by the line core width if the line seems to be abnormally broadened after excluding the magnetic field-induced broadening. For instance, we carry out a Gaussian fit for intensity profiles of the coronal line in all the 25 spatial points of SE204-4 and SE204-6, respectively, and the greatest Doppler widths are found to be, respectively, 0.0684 and 0.0920 nm after the deconvolution of the instrumental profile, while the theoretical width reads as 0.0591 nm, provided that the formation temperature is 2.6 million K and the microturbulent velocity is 15.6 km s −1 (Koutchmy et al 2019). However, even though we know the number of polarization sources along the LOS in the optically thin layers and/or within one subresolution volume, it is still hard to disentangle the remaining unique issue in decomposing the integrated polarization signals to the components.…”

Dual-Mode Hyperspectral Bio-Imager With a Conjugated Camera for Quick Object-Selection and Focusing

“…All the observed spectra show many hollows on the spectral line, especially at 760 nm. This is because the scene is illuminated by sunlight, which gets partially absorbed by water vapor and gas when the sunlight passes through the atmosphere [28,29]. The reflected spectra of the three color dot regions have peaks in the corresponding color bands.…”