Benchmarking the MEKAL spectral code with solar X-ray spectra

With the likelihood that high-resolution soft X-ray spectra of non-solar astronomical sources will soon become available, it is desirable to examine the accuracy of spectral synthesis codes. In this paper, a benchmark study of the MEKAL code, extensively used in the past for spectra from EUVE, ASCA, SAX, and other spacecraft, is presented using high-resolution solar flare X-ray spectra obtained with the Bragg Flat Crystal Spectrometer (FCS) on SMM. Lines in the range 5-20 Angstrom are used to adjust the wavelengths in the MEKAL code. Many of the lines are duc to Fe ions, and arise from 3-2 transitions for spectra obtained during the decay phase of one of the flares, while others arise from higher-excitation (4-2, 5-2 etc.) transitions for spectra obtained near the peak of a second flare. Laboratory measurements of the wavelengths of these lines were also used to confirm the SMM values as well as published identifications from the HULLAC atomic code. The adjustments needed were up to 35 m Angstrom for line wavelengths above 13 Angstrom but much less at shorter wavelengths. Some of these adjustments will be perceptible for spectra from the forthcoming SMM and Chandra spacecraft.