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Abstract Differential emission measure (DEM) inversion methods use the brightness of a set of emission lines to infer the line-of-sight (LOS) distribution of the electron temperature (Te) in the corona. DEM inversions have been traditionally performed with collisionally excited lines at wavelengths in the extreme ultraviolet and X-ray. However, such emission is difficult to observe beyond the inner corona (1.5R⊙), particularly in coronal holes. Given the importance of theTedistribution in the corona for exploring the viability of different heating processes, we introduce an analog of the DEM specifically for radiatively excited coronal emission lines, such as those observed during total solar eclipses (TSEs) and with coronagraphs. This radiative-DEM (R-DEM) inversion utilizes visible and infrared emission lines that are excited by photospheric radiation out to at least 3R⊙. Specifically, we use the Fex(637 nm), Fexi(789 nm), and Fexiv(530 nm) coronal emission lines observed during the 2019 July 2 TSE near solar minimum. We find that, despite a largeTespread in the inner corona, the distribution converges to an almost isothermal yet bimodal distribution beyond 1.4R⊙, withTeranging from 1.1 to 1.4 in coronal holes and from 1.4 to 1.65 MK in quiescent streamers. Application of the R-DEM inversion to the Predictive Science Inc. magnetohydrodynamic simulation for the 2019 eclipse validates the R-DEM method and yields a similar LOSTedistribution to the eclipse data.
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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 ⊙
Abstract We present the spatially resolved absolute brightness of the Fex, Fexi, and Fexivvisible coronal emission lines from 1.08 to 3.4R⊙, 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 Fexiline is found to be the brightest, followed by Fexand Fexiv(in diskB⊙units). All lines had brightness variations between streamers and coronal holes, where Fexivexhibited the largest variation. However, Fexremained surprisingly uniform with latitude. The Fe line brightnesses are used to infer the relative ionic abundances and line-of-sight-averaged electron temperature (Te) 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 inferredTevalues 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 inferredTewithin 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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- Award ID(s):
- 2028173
- PAR ID:
- 10370218
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 935
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 173
- Size(s):
- Article No. 173
- Sponsoring Org:
- National Science Foundation
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