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RHESSI Observations of the Solar Flare Iron-Line Feature at 6.7 keV View all abstracts by submitter

Cristina Chifor   Submitted: 2006-06-22 06:52

Analysis of RHESSI 3 - 10 keV spectra for 27 solar flares is reported. This energy range includes thermal free-free and free-bound continuum and two line features, at ~6.7 keV and ~8 keV, principally due to highly ionized iron (Fe). We used the continuum and the flux in the so-called Fe-line feature at ~6.7 keV to derive the electron temperature Te, the emission measure, and the Fe-line equivalent width as functions of time in each flare. The Fe/H abundance ratio in each flare is derived from the Fe-line equivalent width as a function of Te. To minimize instrumental problems with high count rates and effects associated with multi-temperature and nonthermal spectral components, spectra are presented mostly during the flare decay phase, when the emission measure and temperature were smoothly varying. We found flare Fe/H abundance ratios that are consistent with the coronal abundance of Fe (i.e. 4 times the photospheric abundance) to within 20% for at least 17 of the 27 flares; for 7 flares, the Fe/H abundance ratio is possibly higher by up to a factor of 2. We find evidence that the Fe XXV ion fractions are less than the theoretically predicted values by up to 60% at Te = 12 MK; the observed N(FeXXV)/N(Fe) values appear to be displaced from the most recent theoretical values by between 1 and 3 MK.

Authors: K. J. H. Phillips, C. Chifor & B. Dennis
Projects: RHESSI

Publication Status: Accepted for publication in the Astrophysical Journal; scheduled for the ApJ 20 August 2006, v647n 2 issue.
Last Modified: 2006-06-23 08:50
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