arXiv subjects

K. J. H. Phillips

Publications and source records attributed to K. J. H. Phillips.

At least 19 recordsLinked to original sources

arXiv2022

New Solar Flare Calcium Abundances with no Surprises: Results from the SMM Bent Crystal Spectrometer

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, $A({\rm Ca})$ (expressed logarithmically with $A({\rm H}) = 12$), equal to $6.77 \pm 0.20$ 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 $A({\rm Ca})$ 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 $A({\rm Ca})$ 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.

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arXiv2021

Four decades of advances from MSDP to S4I and SLED imaging spectrometers

The Multichannel Subtractive Double Pass (MSDP) is an imaging spectroscopy technique, which allows observations of spectral line profiles over a 2D field of view with high spatial and temporal resolution. It has been intensively used since 1977 on various spectrographs (Meudon, Pic du Midi, the German Vacuum Tower Telescope, THEMIS, Wrocław). We summarize previous developments and describe the capabilities of a new design that has been developed at Meudon and that has higher spectral resolution and increased channel number: Spectral Sampling with Slicer for Solar Instrumentation (S4I), which can be combined with a new and fast polarimetry analysis. This new generation MSDP technique is well adapted to large telescopes. Also presented are the goals of a derived compact version of the instrument, the Solar Line Emission Dopplerometer (SLED), dedicated to dynamic studies of coronal loops observed in the forbidden iron lines, and prominences. It is designed for observing total solar eclipses, and for deployment on the Wrocław and Lomnicky peak coronagraphs respectively for prominence and coronal observations.

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arXiv2020

A Unique Resource for Solar Flare Diagnostic Studies: the SMM Bent Crystal Spectrometer

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 \caxix\ 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 \caxix\ and \fexxv\ line spectra be used as templates for the analysis of X-ray spectra of non-solar sources.

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arXiv2019

Analysis of Quiescent Corona X-ray Spectra from SphinX during the 2009 Solar Minimum

The SphinX X-ray spectrophotometer on the {\em CORONAS-PHOTON}\/ mission observed the 1~--~15\,keV X-ray spectrum of the spatially integrated solar corona during the deep minimum of 2009, when solar activity was exceptionally low. Its sensitivity for energies $> 1.2$\,keV was higher than that of any other solar X-ray spectrometer in orbit at the time, including the detectors on GOES. Using much improved instrumental data than was used previously, we analyzed SphinX spectra in 576 intervals for which there was no discernible activity (NA), 40 intervals when there were X-ray brightenings (B), and sixteen intervals when there were micro-flares with peak emission less than GOES A1 (F). An instrumental background spectrum, formed over 34 hours of spacecraft night-time periods and including electronic noise and particle radiation, was subtracted from the solar spectra. Theoretical spectra were used to deduce temperatures on an isothermal assumption for the NA, B, and F intervals (1.69, 1.81, and 1.86\,MK respectively). Differential emission measure (DEM) analysis for the same spectra revealed a "cooler" component (log\,$T = 6.2$ or $T \approx 1.6$\,MK) in each case, but with a second hotter component having a less well-defined peak temperature varying from $\approx 2.5$ to $\approx 3.5$\,MK (log\,$T = 6.4$ and 6.55) and an emission measure between two and three orders smaller than that of the cooler component. These results are similar to those obtained at times just after solar minimum with the EVE instrument. A very hot component that might indicate the signature of nano-flare heating of the corona is not evident in SphinX data.

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arXiv2019

Terrestrial modification of the Ivuna meteorite and a reassessment of the chemical composition of the CI type specimen

The rare CI carbonaceous chondrites are the most aqueously altered and chemically primitive meteorites but due to their porous nature and high abundance of volatile elements are susceptible to terrestrial weathering. The Ivuna meteorite, type specimen for the CI chondrites, is the largest twentieth-century CI fall and least affected by terrestrial alteration. The main mass of Ivuna (BM2008 M1) has been stored in a nitrogen atmosphere at least since 2008 and is the most pristine CI chondrite stone. We report the mineralogy, petrography and bulk elemental composition of BM2008 M1 and a second Ivuna stone (BM1996 M4) stored in air. Both Ivuna stones are breccias consisting of multiple rounded, phyllosilicate-rich clasts formed through aqueous alteration followed by impact processing. A polished thin section of BM2008 M1 analysed immediately after preparation was found to contain sulphate-bearing veins formed when primary sulphides reacted with oxygen and atmospheric water. A section of BM1996 M4 lacked veins but had sulphate grains on the surface recently formed (last 6 years). Differences in the extent of terrestrial alteration recorded by BM2008 M1 and BM1996 M4 probably reflect variations in the post-recovery curation history of the stones before entering the NHM collection, and indicate that where possible pristine samples of hydrated carbonaceous should be kept out of the terrestrial environment in a stable environment to avoid modification. The bulk elemental composition of the two Ivuna stones show some variability due to their heterogeneous nature but in general are similar to previous analyses of CI chondrites. We combine our elemental abundances with literature values to calculate a new average composition for the Ivuna meteorite, which is in good agreement with existing compilations of CI chondrites and the most recent solar photospheric abundances.

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arXiv2019

A Search for High-Frequency Coronal Brightness Variations in the 21 August 2017 Total Solar Eclipse

We report on a search for short-period intensity variations in the green-line FeXIV 530.3 nm emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions (1999 and 2001 eclipses), allowing fine details of quiet coronal loops and an active-region loop system to be seen. A guided 200-mm-aperture Schmidt-Cassegrain telescope was used with a state-of-the-art CCD camera having 16-bit intensity discrimination and a field-of-view 0.43 degree x 0.43 degree that encompassed approximately one third of the visible corona. The camera pixel size was 1.55 arcseconds, while the seeing during the eclipse enabled features of approx. 2 arcseconds (1450 km on the Sun) to be resolved. A total of 429 images were recorded during a 122.9 second portion of the totality at a frame rate of 3.49 images per second. In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic (MHD) waves with short periods may be important in quiet coronal and active-region heating. Allowing first for various instrumental and photometric effects, we used a wavelet technique to search for periodicities in some 404 000 pixels in the frequency range 0.5-1.6 Hz (periods: 2 second to 0.6 second). We also searched for travelling waves along some 65 coronal structures. However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations.

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arXiv2018

Highly ionized Calcium and Argon X-ray spectra from a large solar flare

X-ray lines of helium-like calcium (\ion{Ca}{19}) between 3.17~Å and 3.21~Å and associated \ion{Ca}{18} dielectronic satellites have previously been observed in solar flare spectra, and their excitation mechanisms are well established. Dielectronic satellites of lower ionization stages (\ion{Ca}{17}~--~\ion{Ca}{15}) are not as well characterized. Several spectra during a large solar flare in 2001 by the DIOGENESS X-ray spectrometer on the {\em CORONAS-F}\/ spacecraft show the \ion{Ca}{17} and \ion{Ca}{16} satellites as well as lines of ionized argon (\ion{Ar}{17}, \ion{Ar}{16}) 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 {\em GOES}\/ X-ray channels, $T_{\rm GOES}$. Some lines are identified for the first time. Similar spectra from the {\em 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 {\em Solar Maximum Mission}\/ Bent Crystal Spectrometer archive and to X-ray spectra expected from the ChemiX instrument on the Sun-orbiting {\em Interhelioprobe}\/ spacecraft, while the relevance to X-ray spectra from non-solar sources is indicated.

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arXiv2017

New Results from the Solar Maximum Mission Bent Crystal Spectrometer

The Bent Crystal Spectrometer (BCS) onboard the NASA Solar Maximum Mission was part of the X-ray Polychromator, which observed numerous flares and bright active regions from February to November 1980, when operation was suspended as a result of the failure of the spacecraft fine pointing system. Observations resumed following the Space Shuttle SMM Repair Mission in April 1984 and continued until November 1989. BCS spectra have been widely used in the past to obtain temperatures, emission measures, and turbulent and bulk flows during flares, as well as element abundances. Instrumental details including calibration factors not previously published are given here, and the in-orbit performance of the BCS is evaluated. Some significant changes during the mission are described, and recommendations for future instrumentation are made. Using improved estimates for the instrument parameters and operational limits, it is now possible to obtain de-convolved, calibrated spectra that show finer detail than before, providing the means to improved interpretation of the physics of the emitting plasmas. The results indicate how historical, archived data can be re-used to obtain enhanced and new, scientifically valuable results.

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arXiv2015

The X-Ray Line Feature At 3.5 Kev In Galaxy Cluster Spectra

Recent work by Bulbul et al. and Boyarsky et al. has suggested that a line feature at approx. 3.5 keV in the X-ray spectra of galaxy clusters and individual galaxies seen with XMM-Newton is due to the decay of sterile neutrinos, a dark matter candidate. This identification has been criticized by Jeltema and Profumo on the grounds that model spectra suggest that atomic transitions in helium-like potassium (K XVIII) and chlorine (Cl XVI) are more likely to be the emitters. Here it is pointed out that the K XVIII lines have been observed in numerous solar flare spectra at high spectral resolution with the RESIK crystal spectrometer and also appear in Chandra HETG spectra of the coronally active star sigma Gem. In addition, the solar flare spectra at least indicate a mean coronal potassium abundance which is a factor of between 9 and 11 higher than the solar photospheric abundance. This fact, together with the low statistical quality of the XMM-Newton spectra, completely accounts for the approx. 3.5 keV feature and there is therefore no need to invoke a sterile neutrino interpretation of the observed line feature at 3.5 keV.

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arXiv2015

Solar Flare Element Abundances from the Solar Assembly for X-rays (SAX) on MESSENGER

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 {\em 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 $1.66 \pm 0.34$ (Fe), $3.89~\pm~0.76$ (Ca), $1.23~\pm~0.45$ (S), $1.64~\pm~0.66$ (Si), and $2.48~\pm~0.90$ (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 $\sim$7~eV rather than $\sim10$~eV.

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arXiv2015

RESIK Solar X-ray flare element abundances on a non-isothermal assumption

Solar X-ray spectra from the RESIK crystal spectrometer on the {\em CORONAS-F} spacecraft (spectral range $3.3-6.1$~Å) 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 $A({\rm H}) = 12$) averaged for all the flares in the analysis are $A({\rm Si}) = 7.53 \pm 0.08$ (previously $7.89 \pm 0.13$), $A({\rm S}) = 6.91 \pm 0.07$ ($7.16 \pm 0.17$), $A({\rm Ar}) = 6.47 \pm 0.08$ ($6.45 \pm 0.07$), and $A({\rm K}) = 5.73 \pm 0.19$ ($5.86 \pm 0.20$), 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.

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arXiv2014

X-ray Flare Spectra from the DIOGENESS Spectrometer and its concept applied to ChemiX on the Interhelioprobe spacecraft

The {\em DIOGENESS} X-ray crystal spectrometer on the {\em 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 {\em GOES} importance ranging from C9 to X5. The instrument included four scanning flat crystals with wavelength ranges covering the regions of \sixiii\ (6.65~Å), \sxv\ (5.04~Å), and \caxix\ (3.18~Å) X-ray lines and associated dielectronic satellites. Two crystals covering the \caxix\ 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 {\em 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 {\em Interhelioprobe} spacecraft due for launch in 2020 and 2022 that will make a near-encounter (perihelion $\sim 0.3$ a.u.) to the Sun in its orbit. We outline the results that are likely to be obtained.

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arXiv2014

Solar Flare Composition and Thermodynamics from RESIK X-ray Spectra

Previous estimates of the solar flare abundances of Si, S, Cl, Ar, and K from the RESIK X-ray crystal spectrometer on board the CORONAS-F spacecraft were made on the assumption of isothermal X-ray emission. We investigate the effect on these estimates by relaxing this assumption and instead determining the differential emission measure (DEM) or thermal structure of the emitting plasma by re-analyzing RESIK data for a GOES class M1.0 flare on 2002 November~14 (SOL2002-11-14T22:26) for which there was good data coverage. The analysis method uses a maximum-likelihood (Withbroe--Sylwester) routine for evaluating the DEM. In a first step, called here AbuOpt, an optimized set of abundances of Si, S, Ar, and K is found that is consistent with the observed spectra. With these abundances, the differential emission measure evolution during the flare is found. The abundance optimization leads to revised abundances of silicon and sulfur in the flare plasma: $A({\rm S}) = 6.94 \pm 0.06$ and $A({\rm Si}) = 7.56 \pm 0.08$ (on a logarithmic scale with $A({\rm H}) = 12$). Previously determined abundances of Ar, K, and Cl from an isothermal assumption are still the preferred values. During the flare's maximum phase, the X-ray-emitting plasma has a basically two-temperature structure, with the cooler plasma with approximately constant temperature (3--6~MK) and a hotter plasma with temperature $16-21$~MK. Using imaging data from the RHESSI hard X-ray spacecraft, the emission volume of the hot plasma is deduced from which lower limits of the electron density $N_e$ and the thermal content of the plasma are given.

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arXiv2012

Silicon abundance from RESIK solar flare observations

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 Åin 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 Å). The fluxes of the \sixiv Ly-$β$ line (5.217 Å) and the \sixiii $1s^2 - 1s3p$ line (5.688 Å) 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 $A({\rm Si}) = 7.93 \pm .21$ (\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.

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arXiv2012

Sphinx measurements of the 2009 solar minimum x-ray emission

The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1-15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES. Several intervals are identified when the X-ray flux was exceptionally low, and the flux and solar X-ray luminosity are estimated. Spectral fits to the emission at these times give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3 and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode X-ray Telescope, we deduce that most of the emission is from general coronal structures rather than confined features like bright points. For one of 27 intervals of exceptionally low activity identified in the SphinX data, the Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby K and M dwarfs.

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arXiv2012

The Solar Flare Sulphur Abundance from RESIK Observations

The RESIK instrument on {\em CORONAS-F} spacecraft observed several sulphur X-ray lines in three of its four channels covering the wavelength range 3.8-6.1 Å during solar flares. The fluxes are analyzed to give the sulphur abundance. Data are chosen for when the instrument parameters were optimized. The measured fluxes of the \ion{S}{15} $1s^2-1s4p$ ($w4$) line at 4.089 Å gives $A({\rm S}) = 7.16 \pm 0.17$ (abundances on a logarithmic scale with $A({\rm H}) = 12$) which we consider to be the most reliable. Estimates from other lines range from 7.13 to 7.24. The preferred S abundance estimate is very close to recent photospheric abundance estimates and to quiet-Sun solar wind and meteoritic abundances. This implies no fractionation of sulphur by processes tending to enhance the coronal abundance from the photospheric that depend on the first ionization potential (FIP), or that sulphur, though its FIP has an intermediate value of 10.36 eV, acts like a "high-FIP" element.

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arXiv2012

The Solar Flare Iron Abundance

The abundance of iron is measured from emission line complexes at 6.65 keV (Fe line) and 8 keV (Fe/Ni line) in {\em RHESSI} X-ray spectra during solar flares. Spectra during long-duration flares with steady declines were selected, with an isothermal assumption and improved data analysis methods over previous work. Two spectral fitting models give comparable results, viz. an iron abundance that is lower than previous coronal values but higher than photospheric values. In the preferred method, the estimated Fe abundance is $A({\rm Fe}) = 7.91 \pm 0.10$ (on a logarithmic scale, with $A({\rm H}) = 12$), or $2.6 \pm 0.6$ times the photospheric Fe abundance. Our estimate is based on a detailed analysis of 1,898 spectra taken during 20 flares. No variation from flare to flare is indicated. This argues for a fractionation mechanism similar to quiet-Sun plasma. The new value of $A({\rm Fe})$ has important implications for radiation loss curves, which are estimated.

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arXiv2011

The Solar Photospheric-to-Coronal Fe abundance from X-ray Fluorescence Lines

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~Å) 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 $θ$ of the flare, and the temperature $T_e$ 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 $1.6\pm 0.5$ 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.

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