Analysis of a solar active region extreme-ultraviolet spectrum from SERTS-97

Goddard Space Flight Center's Solar EW Research Telescope and Spectrograph was flown on 1997 November 18, carrying an intensified CCD detector and a multilayer-coated toroidal diffraction grating Rith enhanced sensitivity over that of a standard gold-coated grating throughout the instrument's 299-353 Angstrom spectral bandpass. Spectra and spectroheliograms of NOAA Active Region 8108 (N21 degrees, E18 degrees) were obtained with a spectral resolution (instrumental FWHM) of 115 m Angstrom. Nearly 100 emission lines were observed in the spatially averaged active region spectrum. Spectra and spectroheliograms of quiet areas south of the region were also obtained An end-to-end radiometric calibration of the rocket instrument was carried out at the Rutherford-Appleton Laboratory in the same facility that was used to calibrate the Coronal Diagnostic Spectrometer experiment on SOHO and using the same EUV light source. The accuracy of this calibration is confirmed by the excellent agreement between the measured and theoretical values of density- and temperature-insensitive line intensity ratios. Nine emission lines of Fe xv are identified in our spectrum; however, large differences between wavelengths in the CHIANTI database and some of the measured solar wavelengths, as well as inconsistencies of various theoretical intensity ratios, suggest a need for improvement in the Fe xv atomic physics parameters and/or the presence of unidentified blending lines. Density-sensitive line intensity ratios of Fe XI lambda lambda 308.55/352.67, Fe XII lambda lambda 338.27/352.11, Fe XIII lambda 320.80/312.17, and Fe XV lambda lambda 321.78/327.03 yield logarithmic electron densities (in cm(-3)) of 9.92 +/- 0.28, 9.74 +/- 0.28, 9.52 +/- 0.30, and 9.62 +/- 0.26, respectively. Using the strongest emission line observed for each ionization stage of Fe from rr through XVI and Ni XVIII, we find that all of the measured nonthermal line widths yield velocities consistent with 35 km s(-1). The differential emission measure curve derived from the observed line intensities exhibits a relative minimum at log T similar to 5.7, a broad maximum centered around log T similar to 6.3, and a rapid decline for temperatures above log T similar to 6.6.