The solar coronal X-ray spectrum from 15.4 to 23.0 A - Lines from highly ionized calcium and chromium and their usefulness as plasma diagnostics

Abstract

view Abstract Citations (32) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The solar coronal X-ray spectrum from 15.4 to 23.0 A - Lines from highly ionized calcium and chromium and their usefulness as plasma diagnostics McKenzie, D. L. ; Landecker, P. B. Abstract Observations by the SOLEX experiment from the USAF P78-1 satellite are used to examine the 15.4-23.0 Å 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-XVL and Ca XV-XVIII were detected; those undetected were obscured by blending. In addition, a blend of two Cr XVIII lines was observed, and three Cr XVII 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 Cr XV 2p6 1S0-2P5 3d-1P1 (18.497 Å) line is sufficiently strong that it can be used for analysis of both flaring and nonflaring plasmas. Calculations of the collision strength from the ground state to the 2p53d1P1 level and of the Cr ionization equilibrium are needed for optimum use of this line. Theoretical data for the Ca XVI 2P1/2-3d2D3/2 line are available, but the line is too weak to be useful for analysis of nonflaring plasmas. Furthermore, the line is density-sensitive for electron density ne ≥ 1011 cm-3 but is not a good density diagnostic because no non-density-sensitive comparison line from Ca XVI is detectable. The Ca XV line flux ratio, F(2p2 3P2-2p3d3D3)/F(2p2 3P0-2p3d1) is used to estimate flare electron densities at ∼4 × 106 K. The derived densities are in rough agreement with those derived from O VII line ratios at 2 × 106 K. The coronal abundances of Cr and Ca with respect to O are estimated; we find A(Cr)/A(O) = 0.0036 ± 0.0018 and A(Ca)/A(O) = 0.015 ± 0.005. We discuss the determination of these and other abundances by the analysis of X-ray spectra. Publication: The Astrophysical Journal Pub Date: March 1982 DOI: 10.1086/159735 Bibcode: 1982ApJ...254..309M Keywords: Abundance; Plasma Diagnostics; Solar Corona; Solar Spectra; X Ray Spectra; Calcium; Chromium; Line Spectra; Metal Ions; Solar Physics full text sources ADS |