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

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

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  

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

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  

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

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  

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

Publication Status: Accepted for publication, Solar Physics
Last Modified: 2014-11-05 11:49
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Silicon Abundance from RESIK Solar Flare Observations  

Kenneth Phillips   Submitted: 2012-12-13 05:47

The RESIK instrument on the CORONAS-F spacecraft obtained solar flare and active region X-ray spectra in four channels covering the wavelength range 3.8-6.1~AA in its operational period between 2001 and 2003. Several highly ionized silicon lines were observed within the range of the long-wavelength channel (5.00,-,6.05~AA). The fluxes of the sixiv Ly-eta line (5.217~AA) and the sixiii 1s^2 - 1s3p line (5.688~AA) during 21 flares with optimized pulse-height analyzer settings on RESIK have been analyzed to obtain the silicon abundance relative to hydrogen in flare plasmas. As in previous work, the emitting plasma for each spectrum is assumed to be characterized by a single temperature and emission measure given by the ratio of emission in the two channels of GOES. The silicon abundance is determined to be A({ m Si}) = 7.93 pm .21 (sixiv) and 7.89 pm .13 (sixiii) on a logarithmic scale with H = 12. These values, which vary by only very small amounts from flare to flare and times within flares, are 2.6 pm 1.3 and 2.4 pm 0.7 times the photospheric abundance, and are about a factor of three higher than RESIK measurements during a period of very low activity. There is a suggestion that the Si/S abundance ratio increases from active regions to flares.

Authors: B. Sylwester, K. J. H. Phillips, J. Sylwester, A. Kepa
Projects: CORONAS-F

Publication Status: Solar Physics (to be published)
Last Modified: 2012-12-14 16:10
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The Solar Flare Iron Abundance  

Kenneth Phillips   Submitted: 2012-01-13 09:16

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: K. J. H. Phillips, B. R. Dennis
Projects: RHESSI

Publication Status: Accepted by Astrophysical Journal
Last Modified: 2012-01-16 02:22
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The Solar Photospheric-to-Coronal Fe abundance from X-ray Fluorescence Lines  

Kenneth Phillips   Submitted: 2012-01-03 05:44

The ratio of the Fe abundance in the photosphere to that in coronal flare plasmas is determined by X-ray lines within the complex at 6.7 keV (1.9~AA) emitted during flares. The line complex includes the He-like Fe (fexxv) resonance line w (6.70 keV) and Fe K α lines (6.39, 6.40 keV), the latter being primarily formed by the fluorescence of photospheric material by X-rays from the hot flare plasma. The ratio of the Fe K α lines to the fexxv w depends on the ratio of the photospheric-to-flare Fe abundance, heliocentric angle heta of the flare, and the temperature Te of the flaring plasma. Using high-resolution spectra from X-ray spectrometers on the {em P78-1} and {em Solar Maximum Mission} spacecraft, the Fe abundance in flares is estimated to be 1.6pm 0.5 and 2.0 pm 0.3 times the photospheric Fe abundance, the {em P78-1} value being preferred as it is more directly determined. This enhancement is consistent with results from X-ray spectra from the {em RHESSI} spacecraft, but is significantly less than a factor 4 as in previous work.

Authors: K. J. H. Phillips
Projects: Yohkoh-BCS

Publication Status: Accepted by MNRAS
Last Modified: 2012-01-03 08:25
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The Solar Flare Chlorine Abundance from RESIK X-ray Spectra  

Kenneth Phillips   Submitted: 2011-06-08 03:15

The abundance of chlorine is determined from X-ray spectra obtained with theRESIK instrument on {em CORONAS-F} during solar flares between 2002 and 2003.Using weak lines of He-like Cl, ion{Cl}{16}, between 4.44 and 4.50 AA, andwith temperatures and emission measures from {em GOES} on an isothermalassumption, we obtained A({ m Cl}) = 5.75 pm 0.26 on a scale A({ m H}) =12. The uncertainty reflects an approximately factor 2 scatter in measuredline fluxes. Nevertheless our value represents what is probably the best solardetermination yet obtained. It is higher by factors of 1.8 and 2.7 than Clabundance estimates from an infrared sunspot spectrum and nearby ion{H}{2}regions. The constancy of the RESIK abundance values over a large range offlares ({em GOES} class from below C1 to X1) argues for any fractionation thatmay be present in the low solar atmosphere to be independent of the degree ofsolar activity.

Authors: B. Sylwester, K. J. H. Phillips, J. Sylwester, V. D. Kuznetsov
Projects: CORONAS-F/SPIRIT

Publication Status: Accepted by Astrophysical Journal
Last Modified: 2011-06-08 07:48
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The solar X-ray continuum measured by RESIK  

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

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  

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

Publication Status: ApJ Letters (in press)
Last Modified: 2008-09-23 21:00
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Abstracts by Author
Highly Ionized Calcium and Argon X-ray Spectra from a Large Solar Flare
Solar Flare Element Abundances from the Solar Assembly for X-rays (SAX) on MESSENGER
RESIK SOLAR X-RAY FLARE ELEMENT ABUNDANCES ON A NON-ISOTHERMAL ASSUMPTION
X-ray Flare Spectra from the DIOGENESS Spectrometer and its concept applied to ChemiX on the Interhelioprobe spacecraft
Silicon Abundance from RESIK Solar Flare Observations
The Solar Flare Iron Abundance
The Solar Photospheric-to-Coronal Fe abundance from X-ray Fluorescence Lines
The Solar Flare Chlorine Abundance from RESIK X-ray Spectra
The solar X-ray continuum measured by RESIK
New Aspects on Particle Acceleration in Solar Flares from RHESSI Observations

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