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X-ray Line Formation in Astrophysical Environments: The L-shell Spectra of Ionized Iron

Published online by Cambridge University Press:  12 April 2016

Duane A. Liedahl ,
Steven M. Kahn ,
Albert L. Osterheld  and
William H. Goldstein
Duane A. Liedahl
Affiliation:
Department of Physics and Space Sciences LaboratoryUniversity of California, Berkeley, CA, 94720, USA
Steven M. Kahn
Affiliation:
Department of Physics and Space Sciences LaboratoryUniversity of California, Berkeley, CA, 94720, USA
Albert L. Osterheld
Affiliation:
High Temperature Physics Division Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
William H. Goldstein
Affiliation:
High Temperature Physics Division Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA

Abstract

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We have initiated an extensive atomic modeling effort applicable to X-ray line emission in high-temperature astrophysical plasmas. The emphasis of our program is on the detailed accounting of the mechanisms which populate excited states of highly ionized atoms over a wide range of electron temperatures and densities. As a first demonstration we have calculated spectra for the important L -shell ions Fe XVI-XIX in a complete collisional-radiative model under conditions appropriate to solar coronal plasmas. Using methods presented here, we have synthesized the X-ray spectra of solar flares and active regions over the wavelength interval 13 – 18 Ǡ. The atomic model, which includes 705 atomic energy levels, is the largest and most detailed of its kind. In this introductory paper, we discuss the effects of dielectronic recombination on the spectrum of Fe XVII and present a new technique whereby the 3s lines can be used as a diagnostic of the electron temperature. Also included are new values for the rate of resonance excitation of the n=3 Fe XVII excited states. These rates are lower than those previously obtained and suggest that resonance excitation does not contribute significantly to the population kinetics. Finally, we present a direct comparison of our a calculated model spectrum with data from a solar flare.

Type
1. X-rays from a Hot Plasma
Information
International Astronomical Union Colloquium , Volume 115: High Resolution X-ray Spectroscopy of Cosmic Plasmas , 1990 , pp. 49 - 52
Copyright
Copyright © Cambridge University Press 1990

References

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