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Astron. Astrophys. 348, 286-294 (1999)


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The absolute coronal abundances of sulfur, calcium, and iron from Yohkoh-BCS flare spectra

A. Fludra 1 and J.T. Schmelz 2

1 Space Science Department, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK (A.Fludra@rl.ac.uk)
2 Physics Department, University of Memphis, Memphis, TN 38152, USA

Received 1 April 1999 / Accepted 5 May 1999

Abstract

Using X-ray spectra from the Bragg Crystal Spectrometer on Yohkoh , we have derived the absolute coronal abundances of sulfur, calcium, and iron using the ratio of the flux in the S XV, Ca XIX and Fe XXV resonance lines to the continuum near the Ca XIX and S XV resonance lines. For the 57 flares analyzed here, multi-thermal effects have been taken into account using a differential emission measure analysis. We compare these abundances of S, Ca, and Fe with their photospheric values and with values derived for coronal plasma from both spectral and solar energetic particle data. The mean Yohkoh abundance of sulfur relative to hydrogen is [FORMULA], smaller than the photospheric value by over a factor of two. The mean abundance of calcium is [FORMULA], about 50% greater than the photospheric value. The mean abundance of iron shows greater scatter around its mean value of [FORMULA], but is still higher than the accepted photospheric value. Comparison of these results with others already in the literature, suggests that the coronal abundance-normalization problem does not have a simple solution.

Key words: Sun: abundances – Sun: corona – Sun: flares – Sun: X-rays, gamma rays

Send offprint requests to: A. Fludra

© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999

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