The Mysterious Case of the Solar Argon Abundance Near Sunspots in Flares

Doschek, G. A.; Warren, H. P.

doi:10.3847/0004-637x/825/1/36

Cited by 37 publications

(32 citation statements)

References 39 publications

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“…With an assumed Ar/Ca ratio of 0.33 (based on measurements by Sylwester et al (1998) and Sylwester et al (2010a)), the contribution made by the Ar XVII line is comparable to the q line. As pointed out by Sylwester et al (1998), the calcium abundance varies from flare to flare, so the blend may be more or less serious according as the calcium abundance is less or more; an extreme case has been pointed out by Doschek & Warren (2016) who find from ultraviolet line emission near a sunspot that the Ar/Ca abundance ratio may be more than photospheric, equal to around 1.4. On the other hand, a large enhancement of the calcium abundance might occur in flares on active dwarf M stars, if the FIP effect is larger than that apparently operating in the solar atmosphere; thus, the Ar/Ca abundance ratio may be less than our assumed value, reducing the effect of argon line blends.…”

Section: Discussionmentioning

confidence: 95%

Highly Ionized Calcium and Argon X-Ray Spectra from a Large Solar Flare

Phillips

Sylwester

et al. 2018

ApJ

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X-ray lines of helium-like calcium (Ca XIX) between 3.17 Å and 3.21 Å and associated Ca XVIII dielectronic satellites have previously been observed in solar flare spectra, and their excitation mechanisms are well established. Dielectronic satellites of lower ionization stages (Ca XVII -Ca XV) are not as well characterized. Several spectra during a large solar flare in 2001 by the DIOGENESS X-ray spectrometer on the CORONAS-F spacecraft show the Ca XVII and Ca XVI satellites as well as lines of ionized argon (Ar XVII, Ar XVI) including dielectronic satellites. The DIOGENESS spectra are compared with spectra from a synthesis code developed here based on an isothermal assumption with various atomic sources including dielectronic satellite data from the Cowan Hartree-Fock code. Best-fit comparisons are made by varying the temperature as the code's input (Ar/Ca abundance ratio fixed at 0.33); close agreement is achieved although with adjustments to some ion fractions. The derived temperature is close to that derived from the two GOES X-ray channels, T GOES . Some lines are identified for the first time. Similar spectra from the P78-1 spacecraft and the Alcator C-Mod tokamak have also been analyzed and similar agreement obtained. The importance of blends of calcium and argon lines is emphasized, affecting line ratios used for temperature diagnostics. This analysis will be applied to the Solar Maximum Mission Bent Crystal Spectrometer archive and to X-ray spectra expected from the ChemiX instrument on the Sun-orbiting Interhelioprobe spacecraft, while the relevance to X-ray spectra from non-solar sources is indicated.

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Section: Discussionmentioning

confidence: 95%

Highly Ionized Calcium and Argon X-Ray Spectra from a Large Solar Flare

Phillips

Sylwester

et al. 2018

ApJ

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“…This complexity is further complicated by the postulated decrease in abundance from the nominal coronal to photospheric ratio of Ar for the three flares studied in this article and Ca for two of the three flares. The abundances of Ar and Ca have been of recent interest in a Hinode /EIS spectrum (Doschek, Warren, and Feldman, 2015 ; Doschek and Warren, 2016 ), and MinXSS can provide an additional diagnostic in investigating any anomalous behavior. A more rigorous analysis of elemental abundance variations, solar flares, quiescent conditions, and active region evolution comprising DEM fits will be made in the future.…”

Section: Minxss-1 Solar Measurements From Goes A5–m5 Levelsmentioning

confidence: 99%

The Instruments and Capabilities of the Miniature X-Ray Solar Spectrometer (MinXSS) CubeSats

et al. 2018

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The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is the first solar science oriented CubeSat mission flown for the NASA Science Mission Directorate, with the main objective of measuring the solar soft X-ray (SXR) flux and a science goal of determining its influence on Earth’s ionosphere and thermosphere. These observations can also be used to investigate solar quiescent, active region, and flare properties. The MinXSS X-ray instruments consist of a spectrometer, called X123, with a nominal 0.15 keV full-width at half-maximum (FWHM) resolution at 5.9 keV and a broadband X-ray photometer, called XP. Both instruments are designed to obtain measurements from 0.5 – 30 keV at a nominal time cadence of 10 s. A description of the MinXSS instruments, performance capabilities, and relation to the Geostationary Operational Environmental Satellite (GOES) 0.1 – 0.8 nm flux is given in this article. Early MinXSS results demonstrate the capability of measuring variations of the solar spectral soft X-ray (SXR) flux between 0.8 – 12 keV from at least GOES A5–M5 ( ) levels and of inferring physical properties (temperature and emission measure) from the MinXSS data alone. Moreover, coronal elemental abundances can be inferred, specifically for Fe, Ca, Si, Mg, S, Ar, and Ni, when the count rate is sufficiently high at each elemental spectral feature. Additionally, temperature response curves and emission measure loci demonstrate the MinXSS sensitivity to plasma emission at different temperatures. MinXSS observations coupled with those from other solar observatories can help address some of the most compelling questions in solar coronal physics. Finally, simultaneous observations by MinXSS and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) can provide the most spectrally complete soft X-ray solar flare photon flux measurements to date.

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“…Recently, some dramatic new results have been found concerning abundance variations in the corona (Doschek et al 2015;Doschek & Warren 2016, 2017. These results were found from the intensity ratio of the Ca XIV line at 193.87 Å (low FIP) to the nearby Ar XIV line at 194.40 Å (high FIP).…”

Section: Introductionmentioning

confidence: 98%

Photospheric and Coronal Abundances in an X8.3 Class Limb Flare

Doschek

Warren

Harra³

et al. 2018

ApJ

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We analyze solar elemental abundances in coronal post-flare loops of an X8.3 flare (SOL2017-09-10T16:06) observed on the west limb on 2017 September 10 near 18 UT using spectra recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The abundances in the corona can differ from photospheric abundances due to the first ionization potential (FIP) effect. In some loops of this flare, we find that the abundances appear to be coronal at the loop apices or cusps, but steadily transform from coronal to photospheric as the loop footpoint is approached. This result is found from the intensity ratio of a low-FIP ion spectral line (Ca XIV) to a high-FIP ion spectral line (Ar XIV) formed at about the same temperature (4-5 MK). Both lines are observed close in wavelength. Temperature, which could alter the interpretation, does not appear to be a factor based on intensity ratios of Ca XV lines to a Ca XIV line. We discuss the abundance result in terms of the Laming model of the FIP effect, which is explained by the action of the ponderomotive force in magnetohydrodynamic (MHD) waves in coronal loops and in the underlying chromosphere.

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The Mysterious Case of the Solar Argon Abundance Near Sunspots in Flares

Cited by 37 publications

References 39 publications

Highly Ionized Calcium and Argon X-Ray Spectra from a Large Solar Flare

Highly Ionized Calcium and Argon X-Ray Spectra from a Large Solar Flare

The Instruments and Capabilities of the Miniature X-Ray Solar Spectrometer (MinXSS) CubeSats

Photospheric and Coronal Abundances in an X8.3 Class Limb Flare

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