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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.39] Measuring Active Region Temperatures with SERTS and Yohkoh (SXT) Data

J. T. Schmelz (Univ. of Memphis), J. L. R. Saba (Lockheed-Martin), K. T. Strong (Lockheed-Martin)

Often the derived temperature of an active region reflects the method and the nature of the instrument used in its measurement. Yet establishing the temperature is the first step needed to proceed with most of the interesting physics of active regions -- including heating processes, loop stability, and cooling timescales. Accurately characterizing the thermal distribution of the coronal plasma requires data which can resolve multi-thermal features and which also constrain both low- and high-temperature emission.

To model the temperature distribution of NOAA Active Region 7563, we have combined broad-band filter data from the Yohkoh Soft X-ray Telescope (SXT) with simultaneous spectral line data from the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) taken during its flight on 17 August 1993.

>From the SERTS data alone, Brosius et al. (1996) produced a double-peaked differential emission measure (DEM) distribution (see their Figure 8), but the higher-temperature ( 4 MK) peak was at the extreme end of the SERTS range of sensitivity, and so was uncertain. But the higher temperature response of SXT can be used to cross-check the reality of this high-temperature feature -- we adjusted the response functions of the three SXT filters available for this observation by replacing the Meyer (1985) elemental abundances normally used in SXT analysis with the coronal abundance set of Feldman (1992), which was used by Brosius et al. (1996). We then folded the SERTS DEM curve through the adjusted SXT responses, and found that the high-temperature DEM peak was NOT consistent with the SXT data. The SERTS and SXT data sets could be reconciled only if the high-temperature peak was eliminated from the DEM curve.

We also discuss how the SXT responses change with the assumed set of elemental abundances. In particular, a change in the normalization of heavy elements with respect to hydrogen does NOT yield a simple scaling factor in the emission measure, and the temperature responses of filter ratios are also affected.

Brosius et al. 1996, ApJ Suppl., 106, 143. Feldman 1992, Phys. Scr., 46, 202. Meyer 1985, ApJ Suppl., 57,173.

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