34th Solar Physics Division Meeting, June 2003
Session 17 Corona III
Poster, Wednesday, June 18, 2003, 3:30-5:00pm, Mezzanine

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[17.12] A New Fitting Procedure for the Blended He I 1083 nm Multiplet

H.P. Jones (NASA's GSFC), O,V. Malanushenko (NSO)

The He I 1083 nm multiplet is a powerful tool for observing the outer solar atmosphere but is difficult to analyze because the lines are weak, highly variable, and spectrally blended, both internally and with other neighboring solar and telluric lines. After separation from nearby spectral features (see accompanying poster by Malanushenko and Jones), two components of the He I multiplet are resolved. Fitting these lines with two unconstrained Gaussian profiles always gives a ratio of major to minor component of less than half the value which would be expected for optically thin lines. One possibility for explaining the discrepancy between the weakness of the lines and the ratio of the spectral components is to assume that the line formation regions are concentrated in laterally unresolved, optically thick structures with small filling factor. However, we present here a least-squares fitting technique using cubic splines with fixed breakpoints with the constraint that the blend is the sum of three identically shaped profiles shifted in wavelength according to the atomic structure of the blend and weighted by the corresponding statistical weights, in agreement with optically thin line formation. The basis functions for the fitting procedure have no built-in spectral symmetry or shape. The resulting underlying profiles tend to be asymmetric with excess absorption to the blue, consistent with formation by "hot" and "cool" spatial elements within the observed volume, with the hotter regions having differential motion toward the observer. The results agree well with NASA/NSO Spectromagnetograph observations in quiet sun and coronal holes. Partial funding of this research was provided through the NASA Sun-Earth Connection SR&T program.

The author(s) of this abstract have provided an email address for comments about the abstract: hjones@noao.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.