An official website of the United States government
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.
more »
« less
The Solar Minimum Eclipse of 2019 July 2. III. Inferring the Coronal T e with a Radiative Differential Emission Measure Inversion
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.
more »
« less
- Award ID(s):
- 1839436
- PAR ID:
- 10474370
- Editor(s):
- Vishniac, E.
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Edition / Version:
- 1
- Volume:
- 951
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 55
- Subject(s) / Keyword(s):
- Solar corona Solar eclipses Solar coronal streamers Solar coronal holes Solar optical telescopes 1483 1489 1486 1484 1514 Astrophysics - Solar and Stellar Astrophysics
- Format(s):
- Medium: X Size: 5.2MB Other: pdf
- Size(s):
- 5.2MB
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Potential field source surface (PFSS) models are widely used to simulate coronal magnetic fields. PFSS models use the observed photospheric magnetic field as the inner boundary condition and assume a perfectly radial field beyond a “source surface” (Rss). At present, total solar eclipse (TSE) white-light images are the only data that delineate the coronal magnetic field from the photosphere out to several solar radii (R⊙). We utilize a complete solar cycle span of these images between 2008 and 2020 as a benchmark to assess the reliability of PFSS models. For a quantitative assessment, we apply the Rolling Hough Transform to the eclipse data and corresponding PFFS models to measure the difference, Δθ, between the data and model magnetic field lines throughout the corona. We find that the average Δθ, 〈Δθ〉, can be minimized for a given choice ofRssdepending on the phase within a solar cycle. In particular,Rss≈ 1.3R⊙is found to be optimal for solar maximum, whileRss≈ 3R⊙yields a better match at solar minimum. Regardless, large (〈Δθ〉 > 10°) discrepancies between TSE data and PFSS-generated coronal field lines remain regardless of the choice of source surface. However, implementation of solar-cycle-dependentRssoptimal values does yield more reliable PFSS-generated coronal field lines for use in models and for tracing in situ measurements back to their sources at the Sun.more » « less
-
null (Ed.)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.more » « less
-
Abstract The Airborne Infrared Spectrometer (AIR-Spec) was commissioned during the 2017 total solar eclipse, when it observed five infrared coronal emission lines from a Gulfstream V research jet owned by the National Science Foundation and operated by the National Center for Atmospheric Research. The second AIR-Spec research flight took place during the 2019 July 2 total solar eclipse across the south Pacific. The 2019 eclipse flight resulted in seven minutes of observations, during which the instrument measured all four of its target emission lines: S xi 1.393 μ m, Si x 1.431 μ m, S xi 1.921 μ m, and Fe ix 2.853 μ m. The 1.393 μ m S xi line was detected for the first time, and probable first detections were made of Si xi 1.934 μ m and Fe x 1.947 μ m. The 2017 AIR-Spec detection of Fe ix was confirmed and the first observations were made of the Fe ix line intensity as a function of solar radius. Telluric absorption features were used to calibrate the wavelength mapping, instrumental broadening, and throughput of the instrument. AIR-Spec underwent significant upgrades in preparation for the 2019 eclipse observation. The thermal background was reduced by a factor of 30, providing a 5.5× improvement in signal-to-noise ratio, and the postprocessed pointing stability was improved by a factor of 5 to <10″ rms. In addition, two imaging artifacts were identified and resolved, improving the spectral resolution and making the 2019 data easier to interpret.more » « less
-
Abstract The spectra of coronal mass ejections (CMEs) in the low corona play a crucial role in understanding their origins and physical mechanisms and enhancing space weather forecasting. However, capturing these spectra faces significant challenges. This paper introduces a scheme of a multislit spectrometer design with five slits, acquiring the global spectra of the solar corona simultaneously with a focus on the spectra of CMEs in the low corona. The chosen wavelength range of the spectrometer (170–180 Å) includes four extreme ultraviolet emission lines (Fex174.53 Å, Feix171.07 Å, Fex175.26 Å, Fex177.24 Å), which provides information on the plasma velocity, density, and temperature. Utilizing a numerical simulation of the global corona for both the on-disk and the off-limb scenarios, we focus on resolving the ambiguity associated with various Doppler velocity components of CMEs, particularly for a fast CME in the low corona. A new application of our decomposition technique is adopted, enabling the successful identification of multiple discrete CME velocity components. Our findings demonstrate a strong correlation between the synthetic model spectra and the inverted results, indicating the robustness of our decomposition method and its significant potential for global monitoring of the solar corona, including CMEs.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/acd10b
