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

Abstract

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 $\sim 10$~eV.

arXiv commentAccepted for publication, ApJ

References in corpus (11)

• The chemical composition of the Sun
• Ionization balance for optically thin plasmas: rate coefficients for all atoms and ions of the elements H to Ni
• Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere
• A Unified Picture of the FIP and Inverse FIP Effects
• The height of a white-light flare and its hard X-ray sources
• Non-WKB Models of the FIP Effect: The Role of Slow Mode Waves
• Measurements of Absolute Abundances in Solar Flares
• Estimating the properties of hard X-ray solar flares by constraining model parameters
• Solar Flare Composition and Thermodynamics from RESIK X-ray Spectra
• The Solar Flare Iron Abundance
• Highly Ionized Potassium Lines in Solar X-ray Spectra and the Abundance of Potassium

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