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, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 10170090
- Report Number(s):
- UCRL-LR-113985; ON: DE93016999; TRN: 93:002180
- Resource Relation:
- Other Information: DN: Thesis submitted to Univ. of California, Berkeley (US); TH: Thesis (Ph.D.); PBD: Nov 1992
- Country of Publication:
- United States
- Language:
- English
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