The spectral effects of dielectronic recombination in x-ray photoionized plasmas
- Lawrence Livermore National Laboratory, CA (United States)
- California University, Berkeley, CA (United States)
The authors present the results of detailed atomic modeling calculations of the Fe L-shell ions under conditions in which the dominant X-ray producing mechanisms are radiative recombination and dielectronic recombination. This scenario is encountered in X-ray photoionized plasmas, such as those which may exist in the circumsource environments of compact X-ray sources. Highly ionized ions reach their peak abundances at temperatures well below the 'ionization temperature', thereby reducing the importance of electron impact in populating excited states. At these low temperatures, dielectronic recombination can proceed efficiently through radiationless capture of a free electron into a high-n state accompanied by a [Delta]n = 0 core excitation, the Coster-Kronig mechanism. In ions with partially L shells, the relevant [Delta]n = 0 transitions are of the type 2s - 2p. Radiative stabilization of the 'doubly-excited' state completes the recombination, often leaving the recombined ion in an excited state which subsequently decays through a radiative cascade. The Fe L-shell ions, Fe XVIII-XXIV, are especially vulnerable to this process in X-ray photoionized plasmas, since each has several doubly-excited states with 2s vacancies lying just above the ionization limit. At the temperatures expected to exist in the ionization zones of the Fe L-shell ions, the electron energy distribution strongly overlaps these low-lying resonances. The different temperature dependences of competing level populating mechanisms results in several temperature-sensitive line ratios. They discuss the diagnostic potential of line ratios in the X-ray and EUV spectrum of the Fe L-shell ions and their relevance to interpreting spectral data from future astrophysical observatories.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6893106
- Journal Information:
- American Astronomical Society, Bulletin; (United States), Vol. 24:2; ISSN 0002-7537
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
COSMIC X-RAY SOURCES
ULTRAVIOLET SPECTRA
X-RAY SPECTRA
ATOMIC MODELS
ELECTRON CAPTURE
ELEMENT ABUNDANCE
EXTREME ULTRAVIOLET RADIATION
IRON IONS
MULTICHARGED IONS
PHOTOIONIZATION
PLASMA
RECOMBINATION
X RADIATION
ABUNDANCE
CAPTURE
CHARGED PARTICLES
COSMIC RAY SOURCES
ELECTROMAGNETIC RADIATION
IONIZATION
IONIZING RADIATIONS
IONS
MATHEMATICAL MODELS
RADIATIONS
SPECTRA
ULTRAVIOLET RADIATION
661300* - Other Aspects of Physical Science- (1992-)