The Solar Flare Chlorine Abundance from RESIK X-ray Spectra

Abstract

The abundance of chlorine is determined from X-ray spectra obtained with the RESIK 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 Å, and with temperatures and emission measures from {\em GOES} on an isothermal assumption, we obtained $A(\mathrm{Cl})=5.75\pm 0.26$ on a scale $A(\mathrm{H})=12$. The uncertainty reflects an approximately factor 2 scatter in measured line fluxes. Nevertheless our value represents what is probably the best solar determination yet obtained. It is higher by factors of 1.8 and 2.7 than Cl abundance estimates from an infrared sunspot spectrum and nearby \ion{H}{2} regions. The constancy of the RESIK abundance values over a large range of flares ({\em GOES} class from below C1 to X1) argues for any fractionation that may be present in the low solar atmosphere to be independent of the degree of solar activity.

13 pages, 3 colour figures. To be published, Astrophysical Journal

References in corpus (6)

• The chemical composition of the Sun
• On the abundance discrepancy problem in HII regions
• Soft X-ray coronal spectra at low activity levels observed by RESIK
• Highly Ionized Potassium Lines in Solar X-ray Spectra and the Abundance of Potassium
• The solar X-ray continuum measured by RESIK
• A solar spectroscopic absolute abundance of argon from RESIK

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