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C.R. Nevels, J.T. Schmelz, V.L. Richardson (University of Memphis)
A measurement of density is essential when trying to understand the fundamental physics of complex phenomena such as coronal heating and loop dynamics. Plasma densities are usually determined from the ratio of intensities of two spectral lines, ideally from the same element and ionization state in order to eliminate the uncertainties inherent in elemental abundances and the ionization fractions. Instead, we have used the spectral lines of iron observed in active regions during the 1993, 1995, and 1997 SERTS rocket flights. With these data, we produced differential emission measure curves that model the multi-thermal plasma in the field of view. We then varied the density in the range 5 x 108 cm-3 < ne < 5 x 1010 cm-3 in order to minimize the difference between the line intensities observed by the instrument and those predicted by our differential emission measure model. In all three cases, it appeared that a mean electron density could characterize the emitting loops of the stable active regions under study over a fairly large range in temperature. This method of determining density is complementary to standard line-ratio diagnostics. Because it uses a large number of spectral lines simultaneously, it is not weighted heavily by the potential atomic data uncertainties inherent in any given line ratio. Our results lead us to postulate that, at least for stable, quiescent regions, there might in fact be a narrow range of characteristic mean densities over a broad temperature regime. We suggest that this technique might be a powerful new density diagnostic tool. Solar physics research at the University of Memphis is supported by NASA grant NAG5-9783.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.