VARIATIONS IN THE RELATIVE ELEMENTAL ABUNDANCES OF OXYGEN, NEON, MAGNESIUM, AND IRON IN HIGH-TEMPERATURE SOLAR ACTIVE-REGION AND FLARE PLASMAS

We have used X-ray spectral line ratios that are weakly dependent upon temperature to search for evidence of elemental abundance variations in the solar corona. Using spectral lines from Ne IX, O VIII, Fe XVII, Fe XVIII, and Mg XI, we found evidence for Fe/Ne abundance-ratio variations of more than a factor of 4, Fe/O abundance-ratio variations of factors of 2.4-3.1, and O/Ne abundance-ratio variations of approximately a factor of 2. These last variations are the first seen for the abundance ratio of two elements in the "high-FIP" group (those having first ionization potential-FIP-greater than 10 eV). We found no evidence for abundance-ratio variations for Fe and Mg, two low-FIP elements, but the statistics are such that variations as large as a factor of 1.5 cannot be ruled out. The data suggest that a mechanism that favors the promotion of charged species to the corona is operative in the upper chromosphere at a temperature of approximately 1.5 x 10(4) K. The strength of the bias varies both temporally and spatially. We argue that the minimum low-FIP/high-FIP abundance ratios that we observe can be no lower than the photospheric ratios. On this basis, we suggest that the abundance of iron in the photosphere corresponds to that measured in C1 chondrites rather than the higher value obtained by spectroscopic techniques.