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

Jun 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...518.1002g&link_type=abstract

The Astrophysical Journal, Volume 518, Issue 2, pp. 1002-1009.

Astronomy and Astrophysics

Astronomy

25

Atomic Data, Atomic Processes, Line: Formation, Methods: Laboratory, X-Rays: General

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 electrons 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 (kT_e~1.7 keV), the RE contributions arefound 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 existingspectral synthesis codes in common astrophysical use. For the Fe XXIV 3p_3/2-->2s_1/2, 3p_1/2-->2s_1/2, 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.

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