X-ray emission lines from photoionized plasmas
Plasma emission codes have become a standard tool for the analysis of spectroscopic data from cosmic X-ray sources. However, the assumption of collisional equilibrium, typically invoked in these codes, renders them inapplicable to many important astrophysical situations, particularly those involving X-ray photoionized nebulae, which are likely to exist in the circumsource environments of compact X-ray sources. X-ray line production in a photoionized plasma is primarily the result of radiative cascades following recombination. Through the development of atomic models of several highly-charged ions, this work extends the range of applicability of discrete spectral models to plasmas dominated by recombination. Assuming that ambient plasma conditions lie in the temperature range 10[sup 5]--10[sup 6] K and the density range 10[sup 11]--10[sup 16] cm[sup [minus]3], X-ray line spectra are calculated over the wavelength range 5--45 [angstrom] using the HULLAC atomic physics package. Most of the work focuses on the Fe L-shell ions. Line ratios of the form (3s-2p)/(3d-2p) are shown to characterize the principal mode of line excitation, thereby providing a simple signature of photoionization. At electron densities exceeding 10[sup 12] cm[sup [minus]3], metastable state populations in the ground configurations approach their LTE value, resulting in the enrichment of the Fe L-shell recombination spectrum and a set of density-sensitive X-ray line ratios. Radiative recombination continua and emission lines produced selectively by [Delta]n = 0 dielectronic recombination are shown to provide two classes of temperature diagnostics. Because of the extreme overionization, the recombination continua are expected to be narrow ([Delta]E/E [much lt]1), with [Delta]E = kT. Dielectronic recombination selectively drives radiative transitions that originate on states with vacancies in the 2s subshell, states that are inaccessible under pure RR population kinetics.
- Research Organization:
- Lawrence Livermore National Lab., CA (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6327909
- Report Number(s):
- UCRL-LR-113985; ON: DE93016999
- Resource Relation:
- Other Information: Thesis (Ph.D.). Thesis submitted to Univ. of California, Berkeley (United States)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
COSMIC X-RAY SOURCES
EMISSION SPECTRA
IRON IONS
RECOMBINATION
ATOMIC MODELS
ATOMIC PHYSICS
EXCITATION
H CODES
IRON
L SHELL
PHOTOIONIZATION
PLASMA
X-RAY SPECTRA
CHARGED PARTICLES
COMPUTER CODES
COSMIC RAY SOURCES
ELECTRONIC STRUCTURE
ELEMENTS
ENERGY-LEVEL TRANSITIONS
IONIZATION
IONS
MATHEMATICAL MODELS
METALS
PHYSICS
SPECTRA
TRANSITION ELEMENTS
661300* - Other Aspects of Physical Science- (1992-)