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 (1.5
R
⊙
), particularly in coronal holes. Given the importance of the
T
e
distribution 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 3
R
⊙
. Specifically, we use the Fe
x
(637 nm), Fe
xi
(789 nm), and Fe
xiv
(530 nm) coronal emission lines observed during the 2019 July 2 TSE near solar minimum. We find that, despite a large
T
e
spread in the inner corona, the distribution converges to an almost isothermal yet bimodal distribution beyond 1.4
R
⊙
, with
T
e
ranging 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 LOS
T
e
distribution to the eclipse data.
Heavy ions are markers of the physical processes responsible for the density and temperature distribution throughout the fine-scale magnetic structures that define the shape of the solar corona. One ...of their properties, whose empirical determination has remained elusive, is the "freeze-in" distance (Rf) where they reach fixed ionization states that are adhered to during their expansion with the solar wind. We present the first empirical inference of Rf for and derived from multi-wavelength imaging observations of the corresponding Fe xi ( ) 789.2 nm and Fe xiv ( ) 530.3 nm emission acquired during the 2015 March 20 total solar eclipse. We find that the two ions freeze-in at different heliocentric distances. In polar coronal holes (CHs) Rf is around 1.45 R for and below 1.25 R for . Along open field lines in streamer regions, Rf ranges from 1.4 to 2 R for and from 1.5 to 2.2 R for . These first empirical Rf values: (1) reflect the differing plasma parameters between CHs and streamers and structures within them, including prominences and coronal mass ejections; (2) are well below the currently quoted values derived from empirical model studies; and (3) place doubt on the reliability of plasma diagnostics based on the assumption of ionization equilibrium beyond 1.2 R .
Three, broad band capturing, vertically aligned supramolecular triads, R2-BDP-AlPorF3←Im-C60 R = H, styryl (C2H2-Ph), C2H2-TPA (TPA = triphenylamine); ← = coordinate bond, have been constructed using ...BODIPY derivative (BDP, BDP-Ph2 or BDP-TPA2), 5,10,15,20-tetrakis(3,4,5-trifluorophenyl)aluminum(iii) porphyrin (AlPorF3) and fullerene (C60) entities. The C60 and BDP units are bound to the Al center on the opposite faces of the porphyrin: the BDP derivative through a covalent axial bond using a benzoate spacer and the C60 through a coordination bond via an appended imidazole. Owing to the bis-styryl functionality on BDP, the constructed dyads and triads exhibited panchromatic light capture. Due to the diverse absorption and redox properties of the selected entities, it was possible to demonstrate excitation wavelength dependent photochemical events. In the case of the BDP-AlPorF3 dyad, selective excitation of BDP resulted in singlet-singlet energy transfer to AlPorF3 (kEnT = 1.0 × 1010 s-1). On the other hand, excitation of the AlPorF3 entity in the BDP-AlPorF3←Im-C60 triad revealed charge separation leading to the BDP-(AlPorF3)˙+-(C60)˙- charge separated state (kCS = 2.43 × 109 s-1). In the case of the Ph2-BDP-AlPorF3 dyad, energy transfer from 1AlPorF3* to 1(Ph2-BDP)* was witnessed (kEnT = 1.0 × 1010 s-1); however, upon assembling the supramolecular triad, (Ph2-BDP)-AlPorF3←Im-C60, electron transfer from 1AlPorF3* to C60 (kCS = 3.35 × 109 s-1), followed by hole shift (kHS = 1.00 × 109 s-1) to Ph2-BDP, was witnessed. Finally, in the case of the TPA2-BDP-AlPorF3←Im-C60 triad, only electron transfer leading to the (TPA2-BDP)˙+-AlPorF3←Im-(C60)˙- charge separated state, and no energy transfer, was observed. The facile oxidation of Ph2-BDP and TPA2-BDP compared to AlPorF3 in the latter two triads facilitated charge separation through either an electron migration or hole transfer mechanism depending on the initial excitation. The charge-separated states in these triads persisted for about 20 ns.
Abstract The spectroscopic observations presented here were acquired during the 2017 August 21 total solar eclipse (TSE) with a three-channel partially multiplexed imaging spectrometer operating at ...extremely high orders (>50). The 4 R ⊙ extent of the slit in the north–south direction scanned the corona starting from the central meridian out to approximately 1.0 R ⊙ off the east limb throughout totality. The line widths and Doppler shifts of the Fe x (637.4 nm) and Fe xiv (530.3 nm) emission lines, characteristic of 1.1 × 10 6 K and 1.8 × 10 6 K electron temperatures, respectively, varied across the different coronal structures intercepted by the slit. Fe xiv was the dominant emission in the closed fields of an active region and the base of a streamer, with relatively constant 20–30 km s −1 line widths independent of the height. In contrast, Fe x emission exhibited broader (>40 km s −1 ) line widths in open fields, which increased with height, in particular in the polar coronal hole. Inferences of line widths and Doppler shifts were consistent with extreme ultraviolet (EUV) observations from the Hinode/EUV Imaging Spectrograph, as well as with the near-infrared Fe xiii 1074 nm line observed by Coronal Multichannel Polarimeter. The differences in the spectral line widths between distinct coronal structures are interpreted as an indication of the predominance of wave heating in open structures versus localized heating in closed structures. This study underscores the unparalleled advantages and the enormous potential of TSE spectroscopy in measuring line widths simultaneously in open and closed fields at high altitudes, with minimal exposure times, stray light levels, and instrumental widths.
We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 ...min per galaxy, assuming 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code’s results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality’s error bars overlapped 2DFFT’s error bars for 26 of the 30 galaxies. The two methods’ agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies’ spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. All code is freely available.
Lunar Solar Occultation Explorer (Lunasox) Cooper, John F; Habbal, Shadia R; Boe, Benjamin ...
Frontiers in astronomy and space sciences,
06/2023, Letnik:
10
Journal Article
Recenzirano
Odprti dostop
In the present decade and beyond, now 51 years after the last Apollo landing, the NASA Artemis human exploration program will offer abundant opportunities for heliophysics investigations from, by, ...and of the Moon from the vantage points of the lunar orbit and the surface. The Lunar Solar Occultation Explorer (LunaSOX) concept uses the lunar limb to occult the solar disk for high-resolution coronal observations at hourly, daily, to biweekly cadences from spacecraft either in the lunar orbit or at the surface. A 0.2 m diameter solar telescope in orbit with white light and narrow-band visible filters would provide arcsecond spectroscopic imaging of the low-to-high corona (1–10 R☉) with an upper limit of 10–12 B☉ on the local scattered light background from lunar atmospheric dust, as compared to 10–9 B☉ for Earth ground-based solar eclipse observations looking up through the atmosphere at totality. For eclipse observations from and by the Moon, there would be no significant atmospheric disturbances that otherwise limit seeing to arcsec resolution from Earth’s surface. The present eccentric orbits of the ARTEMIS P1 and P2 spacecraft are used as models for a 1 × 10 Rm orbit of LunaSOX to compute the times of solar eclipse intervals, up to 2 hours in duration between the east and west solar hemispheres at a daily cadence for coronal observations at 1–16 R☉ when the orbital aposelene is in anti-sunward directions. In a low-altitude circular orbit and from the surface, the observational cadences would, respectively, be hourly and biweekly. LunaSOX satellites also carrying in situ space environment instruments could integrate into a network of orbital platforms for space weather monitoring and communications relay to far-side surface lander and permanent base sites, e.g., for low-frequency radio cosmology and detection of exoplanet magnetospheres.
Abstract
Total solar eclipses (TSEs) provide a unique opportunity to quantify the properties of the K-corona (electrons), F-corona (dust), and E-corona (ions) continuously from the solar surface out ...to a few solar radii. We apply a novel inversion method to separate emission from the K- and F-corona continua using unpolarized total brightness (
tB
) observations from five 0.5 nm bandpasses acquired during the 2019 July 2 TSE between 529.5 and 788.4 nm. The wavelength dependence relative to the photosphere (i.e., color) of the F-corona itself is used to infer the
tB
of the K- and F-corona for each line of sight. We compare our K-corona emission results with the Mauna Loa Solar Observatory (MLSO) K-Cor polarized brightness (
pB
) observations from the day of the eclipse, and the forward modeled K-corona intensity from the Predictive Science Inc. (PSI) magnetohydrodynamic (MHD) model prediction. Our results are generally consistent with previous work and match both the MLSO data and PSI-MHD predictions quite well, supporting the validity of our approach and of the PSI-MHD model. However, we find that the
tB
of the F-corona is higher than expected in the low corona, perhaps indicating that the F-corona is slightly polarized—challenging the common assumption that the F-corona is entirely unpolarized.
Measuring the global magnetic field of the solar corona remains exceptionally challenging. The fine-scale density structures observed in white-light images taken during total solar eclipses are ...currently the best proxies for inferring the magnetic field direction in the corona from the solar limb out to several solar radii (R ). We present, for the first time, the topology of the coronal magnetic field continuously between 1 and 6 R , as quantitatively inferred with the rolling Hough transform for 14 unique eclipse coronae that span almost two complete solar cycles. We find that the direction of the coronal magnetic field does not become radial until at least 3 R , with a high variance between 1.5 and 3 R at different latitudes and phases of the solar cycle. We find that the most nonradial coronal field topologies occur above regions with weaker magnetic field strengths in the photosphere, while stronger photospheric fields are associated with highly radial field lines in the corona. In addition, we find an abundance of field lines that extend continuously from the solar surface out to several solar radii at all latitudes, regardless of the presence of coronal holes. These results have implications for testing and constraining coronal magnetic field models, and for linking in situ solar wind measurements to their sources at the Sun.
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 (1.5 R⊙), particularly in coronal holes. Given the importance of the Te distribution 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 3 R⊙. Specifically, we use the Fe x (637 nm), Fe xi (789 nm), and Fe xiv (530 nm) coronal emission lines observed during the 2019 July 2 TSE near solar minimum. We find that, despite a large Te spread in the inner corona, the distribution converges to an almost isothermal yet bimodal distribution beyond 1.4 R⊙, with Te ranging 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 LOS Te distribution to the eclipse data.
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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