The Solar Coronal X-Ray Spectrum from 15.4 to 23.0 Angstroms: Lines from Highly Ionized Calcium and Chromium and Their Usefulness as Plasma Diagnostics

摘要

Observations by the SOLEX experiment from the USAF P78-1 satellite are used to examine the 15.4 - 23.0 A X-ray spectrum from both flaring and nonflaring solar active region plasmas. High sensitivity, attained by summing data from several successive spectral scans, enabled the detection of more than 60 lines in this wavelength region. Most of the lines expected to be strongest from Cr XV-XVI and Ca XV-XVIII were detected; those undetected were obscured by belnding. In addition, a blend of two Cr XVIII lines was observed, and three Cr XVIII lines are tentatively identified. Lines from higher ionization states of Cr are at shorter wavelengths and are hard to detect because of strong Fe emission. The Cr and Ca spectra are similar to those of isoelectronic species of Fe. The coronal abundances of Cr and Ca with respect to 0 are estimated; we find A(Cr)/A(0) = 0.0036 + or - 0.0018 and A(Ca)/A(0) = 0.015 + or - 0.005. We discuss the determination of these and other abundances by the analysis of X-ray spectra.