Other
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mwoc.conf...93w&link_type=abstract
Multi-Wavelength Observations of Coronal Structure and Dynamics -- Yohkoh 10th Anniversary Meeting. Proceedings of the conferenc
Other
Scientific paper
Elemental abundances in the corona are known to vary from their photospheric values, and this variation is related to the first ionization potential (FIP) of that element. However, the determination of absolute abundances is difficult in the corona due to the lack of Hydrogen lines emitted at coronal temperatures. Therefore, we are forced either to use relative abundances, but these tell us nothing about the bulk of the plasma, or to chose an empirical model of how the trace elements behave with respect to Hydrogen. Unfortunately, there are competing classifications. One model describes coronal abundances by having the high FIP (> 11.5 eV) elements remain relatively unchanged from their photospheric values while the abundances of low FIP elements (< 10 eV) are enhanced by a factor of about 4. The other model has low FIP elements retain their photospheric abundance values while the high FIP elements are depleted by a factor of about 4. To complicate matters further, the new set of "Hybrid" coronal abundances proposed by Fludra and Schmelz shows low FIP elements are enhanced by about a factor of 2 while high FIP elements are depleted by about the same factor. The Soft X-ray Telescope aboard Yohkoh may seem to be an unlikely candidate in the search for abundance values since it is a broadband instrument and not a spectrometer. However, the abundances chosen to calculate the SXT synthetic spectrum affect not only the instrument response function, but the temperature, emission measure, and differential emission measure results as well.
Cirtain Jonathan W.
Winter Henry D. III
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