Coronal abundances of O, Ne, Mg, and Fe in solar active regions

• Published in: Advances in space research Vol. 13; no. 9; pp. 391 - 394
• Main Authors: Saba, J.L.R., Strong, K.T.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.1993
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/0273-1177(93)90510-I

High resolution soft X-ray spectra acquired with the Flat Crystal Spectrometer on Solar Maximum Mission provide an excellent data base for studying abundances in solar active regions, and testing current ideas on elemental selection by first ionization potential (FIP). The temperature-diagnostic line ratio Fe XVIII/Fe XVII allows removal of the weak temperature dependence of line ratios involving O VIII, Ne IX, Mg XI, and Fe XVII, to determine the relative abundances among the “high-FIP” elements O and Ne, and the “low-FIP” elements Mg and Fe. Significant variability is found for all combinations of relative abundance. The low-FIP/high-FIP Fe:Ne, Mg:Ne, and Mg:O vary by at least a factor of 5; the low-FIP/high-FIP Fe:O, the low-FIP/low-FIP Mg:Fe and the high-FIP/high-FIP Ne:O vary by a factor of 3. The extreme values of the relative abundances depend on the line emissivity calculations used, but the magnitude of variation is about the same for any simple curve through the data. No single set of atomic parameters and ion fractions can account for the observed variations.