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J.W. Cook (NRL), J.S. Newmark (Space Applications Corp.), J.D. Moses (NRL)
We have developed a procedure to produce a differential emission measure (DEM) map of the Sun using images from the four channels of the EIT instrument at 171 (Fe IX/X), 195 (Fe XII), 284 (Fe XV), and 304 A (He II). We use images from the EIT CalRoc sounding rocket flight on 16 October 1997. Our DEM procedure could also be applied to calibrated SOHO EIT images and to TRACE observations. We find that the slope of the DEM distribution over the temperature range log T = 5.5 to 6.0 is typically near +1 for quiet areas, but is +3/2 for active regions. In their thermal structure active regions are not just areas brighter than quiet areas whose DEM distributions continue to rise to even hotter temperatures, but have greater relative amounts of hotter material to cooler material toward 1M K and above than do quiet areas. The DEM should not be modeled in terms of an average structure, either plane parallel or with loop geometry. Since at least the time of the SO82A spectroheliograph observations from Skylab it has been clear that structures observed in the temperature range of any one line differ from structures observed in a hotter or cooler line. Any DEM distribution is obtained from intensity observations through all structures in the line-of-sight, and is composed from the combined individual DEM distributions of these structures. We interpret the DEM map in terms of ensembles of individual loops of differing temperatures, where the ensembles are characteristically different in quiet and active areas of the Sun.
This work is supported by NASA under DPR S-92385-D and by the Office of Naval Research.
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