Laboratory Measurements of Fe XXIV Line Emission: 3->2 Transitions near Excitation Threshold

Details Laboratory Measurements of Fe XXIV Line Emission: 3->2 Transitions near Excitation Threshold Laboratory Measurements of Fe XXIV Line Emission: 3->2 Transitions near Excitation Threshold

Apr 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999head....4.3309g&link_type=abstract

American Astronomical Society, HEAD meeting #4, #33.09; Bulletin of the American Astronomical Society, Vol. 31, p.736

Astronomy and Astrophysics

Astrophysics

Scientific paper

Using the Electron Beam Ion Trap facility at Lawrence Livermore National Laboratory, we have measured relative cross sections for Fe XXIV line emission at electron energies between 0.7 and 3.0 keV. The measurements include line formation by direct electron-impact excitation (DE), radiative cascades, resonant excitation (RE), and dielectronic recombination (DR) satellites with captured electron in n>=5 levels. Good agreement with R-matrix and distorted wave calculations is found. In collisionally ionized plasmas, at temperatures near where the ion abundance peaks (kTe ~ 1.7 keV), the RE contributions are found to be ≲ 5% of the line emission, while the DR satellites contribute ≲ 10%. While good agreement with state-of-the-art atomic physics calculations is found, there is less good agreement with existing spectral synthesis codes in common astrophysical use. For the Fe XXIV 3p_{3/2}-> 2s_{1/2}, 3d_{3/2}-> 2p_{3/2}, and 3d_{5/2}-> 2p_{3/2} transitions, the synthesis code MEKAL underestimates the emissivity in coronal equilibrium by ~ 20% at temperatures near where the ion abundance peaks. In situations where the ionization balance is not solely determined by the electron temperature, RE and DR satellites may contribute a considerable fraction of the line emission. Work at Lawrence Livermore National Laboratory was performed under the auspices of the US Department of Energy under contract No. W-7405-ENG-48. This program is supported by a NASA High Energy Astrophysics X-Ray Astronomy Research and Analysis grant NAGW-4185 (Columbia University) and work order W-19127 (LLNL). The work at Kansas State University is supported by Division of Chemical Science, Office of Basic Energy Research, U.S. Department of Energy.

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