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G. V. Brown (NASA/GSFC and The Johns Hopkins University), P. Beiersdorfer (Physics and Advanced Technology, LLNL), K. R. Boyce (NASA/GSFC), H. Chen (Physics and Advanced Technology, LLNL), S. M. Kahn (Stanford University), R. L. Kelley, C. A. Kilbourne, F. S. Porter (NASA/GSFC), A. Szymkowiak (Yale University)
The mixing of atomic and macroscopic processes taking place in non-terrestrial objects creates complex, dynamic, and intriguing environments. High-resolution x-ray spectra from these sources measured by satellites such as the Chandra X-ray Observatory, XMM-Newton, and the Solar Maximum Mission provide a means for understanding the physics governing these sources. Laboratory measurements of the atomic processes have proved crucial to the interpretation of these spectra. For example, using the LLNL electron beam ion traps EBIT-I & EBHIT-II a detailed study of the x-ray spectrum of Fe {\sc xvii} has been conducted addressing the large ratio predicted by theory compared to observations for the relative intensity of the 2p-3d 1P1 resonance to 3D1 intercombination line. The difference was often attributed to opacity effects. However, laboratory measurements in the optically thin limit agree with observations demonstrating that the prediction is too large. The laboratory results thus provide a benchmark in the optically thin limit for accurate estimates of opacity effects. To uncover the source of the discrepancy between theory and observation, we have performed a series of experiments that successively uncovered more details about the Fe XVII lines produced in coronal plasmas. Most recently, we used NASA's 32 channel array microcalorimeter from the Astro-E x-ray satellite program to measure the excitation cross section of various Fe XVII lines in the laboratory. Our results show that the theoretically predicted cross section for the resonance line is too large while the value for the intercombination line is correct. These measurements resolve long-standing issues thought to be associated with non-equilibrium processes.
Work at LLNL was completed under the auspices of the U.S. D.o.E by the University of California Lawrence Livermore National Laboratory under contract W-7405-Eng-48 and supported by NASA’s Astronomy and Physics Research and Analysis Program under work order S-06553-G
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.