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1. New Observations of the IR Emission Corona from the 2019 July 2 Eclipse Flight of the Airborne Infrared Spectrometer

   https://doi.org/10.3847/1538-4357/ac6ce8  

   Samra, Jenna E.; Madsen, Chad A.; Cheimets, Peter; DeLuca, Edward E.; Golub, Leon; Marquez, Vanessa; Reyes, Naylynn Tañón (July 2022, The Astrophysical Journal)

   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: Sxi1.393μm, Six1.431μm, Sxi1.921μm, and Feix2.853μm. The 1.393μm Sxiline was detected for the first time, and probable first detections were made of Sixi1.934μm and Fex1.947μm. The 2017 AIR-Spec detection of Feixwas confirmed and the first observations were made of the Feixline 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. 

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2. The Solar Minimum Eclipse of 2019 July 2. III. Inferring the Coronal T _e with a Radiative Differential Emission Measure Inversion

   https://doi.org/10.3847/1538-4357/acd10b  

   Boe, Benjamin; Downs, Cooper; Habbal, Shadia (July 2023, The Astrophysical Journal)

   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 (T_e) 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 theT_edistribution 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 largeT_espread in the inner corona, the distribution converges to an almost isothermal yet bimodal distribution beyond 1.4R_⊙, withT_eranging 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 LOST_edistribution to the eclipse data. 

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3. Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST

   https://doi.org/10.3847/2041-8213/ad5186  

   Rho, J; Park, S-H; Arendt, R; Matsuura, M; Milisavljevic, D; Temim, T; De_Looze, I; Blair, W P; Rest, A; Fox, O; et al (June 2024, The Astrophysical Journal Letters)

   Abstract We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec Integral Field Unit (IFU) spectroscopy of the young Galactic supernova remnant Cassiopeia A (Cas A) to probe the physical conditions for molecular CO formation and destruction in supernova ejecta. We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the re-formation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3–5.5μm) were obtained toward two representative knots in the NE and S fields that show very different nucleosynthesis characteristics. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Arvi] and relatively weaker, variable strength ejecta lines of [Siix], [Caiv], [Cav], and [Mgiv]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudocontinuum underneath, which is attributed to the high-velocity widths of CO lines. Our results with LTE modeling of CO emission indicate a temperature of ∼1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe. 

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4. 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 _⊙

   https://doi.org/10.3847/1538-4357/ac8101  

   Boe, Benjamin; Habbal, Shadia; Downs, Cooper; Druckmüller, Miloslav (August 2022, The Astrophysical Journal)

   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 (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 inferredT_evalues 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 inferredT_ewithin 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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5. A JWST Near- and Mid-infrared Nebular Spectrum of the Type Ia Supernova 2021aefx

   https://doi.org/10.3847/2041-8213/acb4ec  

   Kwok, Lindsey A.; Jha, Saurabh W.; Temim, Tea; Fox, Ori D.; Larison, Conor; Camacho-Neves, Yssavo; Brenner Newman, Max J.; Pierel, Justin D. R.; Foley, Ryan J.; Andrews, Jennifer E.; et al (February 2023, The Astrophysical Journal Letters)

   Abstract We present JWST near-infrared (NIR) and mid-infrared (MIR) spectroscopic observations of the nearby normal Type Ia supernova (SN) SN 2021aefx in the nebular phase at +255 days past maximum light. Our Near Infrared Spectrograph (NIRSpec) and Mid Infrared Instrument observations, combined with ground-based optical data from the South African Large Telescope, constitute the first complete optical+NIR+MIR nebular SN Ia spectrum covering 0.3–14μm. This spectrum unveils the previously unobserved 2.5−5μm region, revealing strong nebular iron and stable nickel emission, indicative of high-density burning that can constrain the progenitor mass. The data show a significant improvement in sensitivity and resolution compared to previous Spitzer MIR data. We identify numerous NIR and MIR nebular emission lines from iron-group elements as well as lines from the intermediate-mass element argon. The argon lines extend to higher velocities than the iron-group elements, suggesting stratified ejecta that are a hallmark of delayed-detonation or double-detonation SN Ia models. We present fits to simple geometric line profiles to features beyond 1.2μm and find that most lines are consistent with Gaussian or spherical emission distributions, while the [Ariii] 8.99μm line has a distinctively flat-topped profile indicating a thick spherical shell of emission. Using our line profile fits, we investigate the emissivity structure of SN 2021aefx and measure kinematic properties. Continued observations of SN 2021aefx and other SNe Ia with JWST will be transformative to the study of SN Ia composition, ionization structure, density, and temperature, and will provide important constraints on SN Ia progenitor and explosion models. 

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