New Solar Flare Calcium Abundances with no Surprises: Results from the SMM Bent Crystal Spectrometer |
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Kenneth Phillips Submitted: 2022-03-07 03:23
The calcium abundance in flare plasmas is estimated using X-ray spectra from the Solar Maximum Mission Bent Crystal Spectrometer (BCS) during the decays of 194 flares (GOES classifications from B6.4 to X13) occurring between 1980 and 1989. Previous work by Sylwester et al. found that the abundance varied from flare to flare. That analysis is improved on here using updated instrument parameters and by including all calcium lines viewed by the BCS instead of only the resonance line, so greatly enhancing the photon count statistics. The abundance variations are confirmed with the average abundance, A({ Ca}) (expressed logarithmically with A({ H}) = 12), equal to 6.77 ± 0.20 for 194 flares (141 of which are new in this study). This range corresponds to factors of between 1.7 and 7.2 larger than the photospheric abundance and so our results are in line with a ``FIP" (first ionization potential) effect whereby low-FIP elements like Ca (FIP = 6.11~eV) have enhanced coronal abundances. The Ca flare abundance is uncorrelated with solar activity indices, but weak correlations are suggested with GOES flare class and duration (larger A({ Ca}) for smaller and shorter flares). The ponderomotive force theory of Laming explaining the FIP effect gives a range of parameters within which our estimates of A({ Ca}) agree with the theory. However, this then gives rise to disagreements with previous estimates of the flare silicon and sulfur abundances, although those of argon and iron are in good agreement. Small adjustments of the theory may thus be necessary.
Authors: J. Sylwester, B. Sylwester, K. J. H. Phillips, A. Kepa
Projects: Solar Max Misson
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Publication Status: Accepted, Astrophysical Journal
Last Modified: 2022-03-07 12:57
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A Unique Resource for Solar Flare Diagnostic Studies: the SMM Bent Crystal Spectrometer |
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Kenneth Phillips Submitted: 2020-05-11 06:26
The Bent Crystal Spectrometer (BCS) on the NASA Solar Maximum Mission spacecraft observed the X-ray spectra of numerous solar flares during the periods 1980 February to November and 1984-1989. The instrument, the first of its kind to use curved crystal technology, observed the resonance lines of He-like Ca (caxix) and Fe (fexxv) and neighboring satellite lines, allowing the study of the rapid evolution of flare plasma temperature, turbulence, mass motions etc. To date there has not been a solar X-ray spectrometer with comparable spectral and time resolution, while subsequent solar cycles have delivered far fewer and less intense flares. The BCS data archive thus offers an unparalleled resource for flare studies. A recent re-assessment of the BCS calibration and its operations is extended here by using data during a spacecraft scan in the course of a flare on 1980 November 6 that highlights small deformations in the crystal curvature of the important channel~1 (viewing lines of Ca XIX and satellites). The results explain long-standing anomalies in spectral line ratios which have been widely discussed in the past. We also provide an in-flight estimation of the BCS collimator field of view which improves the absolute intensity calibration of the BCS. The BCS channel~1 background is shown to be entirely due to solar continuum radiation, confirming earlier analyses implying a time-variable flare abundance of Ca. We suggest that BCS high-resolution Ca XIX and Fe XXV line spectra be used as templates for the analysis of X-ray spectra of non-solar sources.
Authors: J. Sylwester, B. Sylwester, K. J. H. Phillips, A. Kepa, C. G. Rapley
Projects: Solar Max Misson
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Publication Status: The Astrophysical Journal, to be published (May 2020)
Last Modified: 2020-05-11 15:28
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Highly Ionized Calcium and Argon X-ray Spectra from a Large Solar Flare |
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Kenneth Phillips Submitted: 2018-07-28 05:28
X-ray lines of helium-like calcium (Ca XIX) between 3.17 and 3.21 Angstroms 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.
Authors: K. J. H. Phillips, J. Sylwester, B. Sylwester, M. Kowalinski, M. Siarkowski, W. Trzebinski, S. Plocieniak, and Z. Kordylewski
Projects: CORONAS-F
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Publication Status: Accepted for publication, The Astrophysical Journal
Last Modified: 2018-07-29 21:11
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Solar Flare Element Abundances from the Solar Assembly for X-rays (SAX) on MESSENGER |
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Kenneth Phillips Submitted: 2015-03-06 03:51
X-ray spectra in the range 1.5-8.5 keV have been analyzed for 526 large flares detected with the Solar Assembly for X-rays (SAX) on the Mercury MESSENGER spacecraft between 2007 and 2013. For each flare, the temperature and emission measure of the emitting plasma were determined from the spectrum of the continuum. In addition, with the SAX energy resolution of 0.6 keV (FWHM) at 6 keV, the intensities of the clearly resolved Fe-line complex at 6.7 keV and the Ca-line complex at 3.9 keV were determined, along with those of unresolved line complexes from S, Si, and Ar at lower energies. Comparisons of these line intensities with theoretical spectra allow the abundances of these elements relative to hydrogen to be derived, with uncertainties due to instrument calibration and the unknown temperature distribution of the emitting plasma. While significant deviations are found for the abundances of Fe and Ca from flare to flare, the abundances averaged over all flares are found to be enhanced over photospheric values by factors of 1.66 ± 0.34 (Fe), 3.89 ± 0.76 (Ca), 1.23 ± 0.45 (S), 1.64 ± 0.66 (Si), and 2.48 ± 0.90 (Ar). These factors differ from previous reported values for Fe and Si at least. They suggest a more complex relation of abundance enhancement with the first ionization potential (FIP) of the element than previously considered, with the possibility that fractionation occurs in flares for elements with a FIP of less than approx. 7 eV rather than approx. 10 eV.
Authors: B. R. Dennis, K. J. H. Phillips, R. A. Schwartz, A. K. Tolbert, R. D. Starr, and L. R. Nittler
Projects: Other
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Publication Status: Accepted for publication, The Astrophysical Journal
Last Modified: 2015-03-11 14:49
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RESIK SOLAR X-RAY FLARE ELEMENT ABUNDANCES ON A NON-ISOTHERMAL ASSUMPTION |
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Kenneth Phillips Submitted: 2015-03-04 03:10
Solar X-ray spectra from the RESIK crystal spectrometer on the CORONAS-F spacecraft (spectral range 3.3-6.1A are analyzed for thirty-three flares using a method to derive abundances of Si, S, Ar, and K, emission lines of which feature prominently in the spectra. For each spectrum, the method first optimizes element abundances then derives the differential emission measure as a function of temperature based on a procedure given by Sylwester et al. and Withbroe. This contrasts with our previous analyses of RESIK spectra in which an isothermal assumption was used. The revised abundances (on a logarithmic scale with A(H) = 12) averaged for all the flares in the analysis are A(Si) = 7.53 ± 0.08 (previously 7.89 ± 0.13), A(S) = 6.91 ± 0.07 (7.16 ± 0.17), A(Ar) = 6.47 ± 0.08 (6.45 ± 0.07), and A(K) = 5.73 ± 0.19 (5.86 ± 0.20), with little evidence for time variations of abundances within the evolution of each flare. Our previous estimates of the Ar and K flare abundances are thus confirmed by this analysis but those for Si and S are reduced. This suggests the flare abundances of Si and Ar are very close to the photospheric abundance or solar proxies, while S is significantly less than photospheric and the K abundance is much higher than photospheric. These estimates differ to some extent from those in which a single enhancement factor applies to elements with first ionization potential less than 10~eV.
Authors: B. Sylwester, K. J. H. Phillips, J. Sylwester, A.. Kepa
Projects: CORONAS-F/RESIK
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Publication Status: Accepted for publication, The Astrophysical Journal
Last Modified: 2015-03-04 11:12
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X-ray Flare Spectra from the DIOGENESS Spectrometer and its concept applied to ChemiX on the Interhelioprobe spacecraft |
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Kenneth Phillips Submitted: 2014-11-05 03:09
The DIOGENESS X-ray crystal spectrometer on the CORONAS-F spacecraft operated for a single month (25~August to 17~September) in 2001 but in its short lifetime obtained one hundred and forty high-resolution spectra from some eight solar flares with GOES importance ranging from C9 to X5. The instrument included four scanning flat crystals with wavelength ranges covering the regions of Si XIII (6.65 Angstroms), S XV (5.04 Angstroms), and Ca XIX (3.18 Angstroms) X-ray lines and associated dielectronic satellites. Two crystals covering the Ca XIX lines were oriented in a ``Dopplerometer'' manner, i.e. such that spatial and spectral displacements both of which commonly occur in flares can be separated. We describe the DIOGENESS spectrometer and the spectra obtained during flares which include lines not hitherto seen from spacecraft instruments. An instrument with very similar concept is presently being built for the two Russian Interhelioprobe spacecraft due for launch in 2020 and 2022 that will make a near-encounter (perihelion approx. 0.3 a.u.) to the Sun in its orbit. We outline the results that are likely to be obtained.
Authors: J. Sylwester, Z. Kordylewski, S. Plocieniak, M. Siarkowski, M. Kowalinski, S. Nowak, W. Trzebinski, M. Steslicki, B. Sylwester, E. Stanczyk, R. Zawerbny, Z. Szaforz, K. J. H. Phillips, F. Farnik, A. Stepanov
Projects: None
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Publication Status: Accepted for publication, Solar Physics
Last Modified: 2014-11-05 11:49
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The solar X-ray continuum measured by RESIK |
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Kenneth Phillips Submitted: 2010-01-14 04:12
The solar X-ray continuum emission at five wavelengths between 3.495 Angstroms and 4.220 Angstroms for 19 flares in a seven-month period in 2002-2003 was observed by the RESIK crystal spectrometer on CORONAS-F. In this wavelength region, free-free and free-bound emissions have comparable fluxes. With a pulse-height analyzer having settings close to optimal, the fluorescence background was removed so that RESIK measured true solar continuum in these bands with an uncertainty in the absolute calibration of plus or minus 20 per cent. With an isothermal assumption, and temperature and emission measure derived from the ratio of the two GOES channels, the observed continuum emission normalized to an emission measure of 1048 cm-3 was compared with theoretical continua using the CHIANTI atomic code. The accuracy of the RESIK measurements allows photospheric and coronal abundance sets, important for the free-bound continuum, to be discriminated. It is found that there is agreement to about 25 per cent of the measured continua with those calculated from CHIANTI assuming coronal abundances in which Mg, Si, Fe abundances are four times photospheric.
Authors: K. J. H. Phillips, J. Sylwester, B. Sylwester, V. D. Kuznetsov
Projects: CORONAS-F/SPIRIT
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Publication Status: To be published, ApJ
Last Modified: 2010-01-14 10:14
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New Aspects on Particle Acceleration in Solar Flares from RHESSI Observations |
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Kenneth Phillips Submitted: 2008-06-09 07:26
The Ar XVII X-ray line group principally due to transitions 1s2 - 1s2l (l=s, p) near
4 Angstroms was observed in numerous flares by the RESIK bent crystal spectrometer aboard
CORONAS-F between 2001 and 2003. The three line features include the Ar XVII w (resonance
line), a blend of x and y (intercombination lines), and z (forbidden line), all of which are
blended with Ar XVI dielectronic satellites. The ratio G, equal to [I(x)+I(y) +
I(z)]/I(w), varies with electron temperature T mostly because of unresolved dielectronic
satellites. With temperatures estimated from GOES X-ray emission, the observed G ratios
agree fairly well with those calculated from CHIANTI and other data. With a two-component
emission measure, better agreement is achieved. Some S XV and S XVI lines blend with
the Ar lines, the effect of which occurs at temperatures >8 MK, allowing the S/Ar
abundance ratio to be determined. This is found to agree with coronal values. A nonthermal
contribution is indicated for some spectra in the repeating-pulse flare of 2003 February 6.
Authors: J. Sylwester, B. Sylwester, K. J. H. Phillips
Projects: CORONAS-F/SPIRIT
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Publication Status: ApJ Letters (in press)
Last Modified: 2008-09-23 21:00
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