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Abstract We present the spatially resolved absolute brightness of the Fe x , Fe xi , and Fe xiv visible coronal emission lines from 1.08 to 3.4 R ⊙ , observed during the 2019 July 2 total solar eclipse (TSE). The morphology of the corona was typical of solar minimum, with a dipole field dominance showcased by large polar coronal holes and a broad equatorial streamer belt. The Fe xi line is found to be the brightest, followed by Fe x and Fe xiv (in disk B ⊙ units). All lines had brightness variations between streamers and coronal holes, where Fe xiv exhibited the largest variation. However, Fe x remained surprisingly uniform with latitude. The Fe line brightnesses are used to infer the relative ionic abundances and line-of-sight-averaged electron temperature ( T e ) throughout the corona, yielding values from 1.25 to 1.4 MK in coronal holes and up to 1.65 MK in the core of streamers. The line brightnesses and inferred T e values are then quantitatively compared to the Predictive Science Inc. magnetohydrodynamic model prediction for this TSE. The MHD model predicted the Fe lines rather well in general, while the forward-modeled line ratios slightly underestimated the observationally inferred T e within 5%–10% averaged over the entire corona. Larger discrepancies in the polar coronal holes may point to insufficient heating and/or other limitations in the approach. These comparisons highlight the importance of TSE observations for constraining models of the corona and solar wind formation.
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Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle
This Letter capitalizes on a unique set of total solar eclipse observations, acquired between 2006 and 2020, in white light, \ion[Fe xi] 789.2 nm (\Tfexi\ = $$1.2 \pm 0.1$$ MK) and \ion[Fe xiv] 530.3 nm (\Tfexiv\ = $$ 1.8 \pm 0.1$$ MK) emission. They are complemented by \insitu\ Fe charge state and proton speed measurements from ACE/SWEPAM-SWICS, to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquitous presence of open structures throughout the corona, invariably associated with \ion[Fe xi] emission from $$\rm Fe^{10+}$$, thus revealing a constant electron temperature, \Tc\ = \Tfexi\, in the expanding corona. The \insitu\ Fe charge states are found to cluster around $$\rm Fe^{10+}$$, independently of the 300 to 700 km $$\rm s^{-1}$$ stream speeds, referred to as the continual solar wind. $$\rm Fe^{10+}$$ thus yields the fiducial link between the continual solar wind and its \Tfexi\ sources at the Sun. While the spatial distribution of \ion[Fe xiv] emission, from $$\rm Fe^{13+}$$, associated with streamers, changes throughout the solar cycle, the sporadic appearance of charge states $$> \rm Fe^{11+}$$, \insitu, exhibits no cycle dependence regardless of speed. These latter streams are conjectured to be released from hot coronal plasmas at temperatures $$\ge \rm $$ \Tfexiv\ within the bulge of streamers and from active regions, driven by the dynamic behavior of prominences magnetically linked to them. The discovery of continual streams of slow, intermediate and fast solar wind, characterized by the same \Tfexi\ in the expanding corona, places new constraints on the physical processes shaping the solar wind.
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- Award ID(s):
- 1839436
- PAR ID:
- 10221752
- Date Published:
- Journal Name:
- The astrophysical journal
- Volume:
- 911
- Issue:
- L4
- ISSN:
- 2041-8213
- Page Range / eLocation ID:
- 14
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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