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
-
-
We present narrowband observations of the Fe xiv (530.3 nm), Fe x (637.4 nm), and Fe xi (789.2 nm) coronal emission lines from the 2023 April 20 Total Solar Eclipse in Australia. We deployed pairs of telescopes for each emission line that were equipped with narrowband filters centered on, and several nanometers away from, the center wavelengths of the lines. The secondary continuum telescopes were used to measure and remove the combined continuum K- (electron) and F- (dust) corona, which dominate coronal emission at optical and infrared wavelengths. Significant emission was detected from all three lines from 1.03 solar radii (R⊙) continuously outward to at least 6 R⊙. The brightness of the lines and continuum are absolutely calibrated to the solar disk, and are validated by a comparison with LASCO-C2 observations made at the same time. Using these observations, we inferred the line emission ratios resolved throughout the middle-corona (defined as 1.5–6 R⊙) for the first time. These line ratios are a probe of the electron temperature, which have important implications for constraining models of coronal heating and the characterization of solar wind formation, yet these emission lines have scarcely been quantified beyond 3 R⊙ in the corona. This study demonstrates the enduring potential of eclipse observations for coronal physics and suggests that future spacecraft missions could observe these lines farther out than has been attempted previously.more » « less
-
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
-
The plasma of the solar corona harbors a multitude of coronal wave modes, some of which could be dissipated to provide the required energy and momentum to heat the corona and accelerate the solar wind. We present observations of the corona acquired with the newly commissioned infrared slit spectropolarimeter Cryo-NIRSP at the Daniel K. Inouye Solar Telescope (DKIST), Haleakalā, Hawaii to study the high-frequency wave behavior in closed, active region structures. Cryo-NIRSP observes the corona off the limb in the Fexiii1074 and 1079 nm forbidden atomic lines. The large aperture of DKIST allows us to explore the active region corona with a temporal resolution faster than a second with an achieved spatial resolution of 2″–5″. Enhanced wave power is observed in the coronal power spectra up to 100 mHz. We report evidence for spectroscopic detection of magnetohydrodynamic (MHD) wave modes with periodicities between 30 and 100 s in the observed active region corona and report their changing properties with height. Furthermore, we report on a statistically significant anticorrelation between the Fexiii1074 nm peak line intensity and line width. These observations show how the powerful spectropolarimetric capabilities of DKIST offer great promise for furthering our knowledge of coronal MHD waves.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/acd10b
