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High Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength {Problem

TitleHigh Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength {Problem
Publication TypeJournal Article
Year of Publication2020
AuthorsS. Kuehn, C. Shah, J. R. Crespo Lopez-Urrutia, K. Fujii, R. Steinbruegge, J. Stierhof, M. Togawa, Z. Harman, N. S. Oreshkina, C. Cheung, M. G. Kozlov, S. G. Porsev, M. S. Safronova, J. C. Berengut, M. Rosner, M. Bissinger, R. Ballhausen, N. Hell, SN. Park, M. Chung, M. Hoesch, J. Seltmann, A. S. Surzhykov, V. A. Yerokhin, J. Wilms, S. F. Porter, T. Stoehlker, C. H. Keitel, T. Pfeifer, , M. A. Leutenegger, and S. Bernitt
JournalPhys. Rev. Lett.
Volume124
Date Publishedjun
ISSN0031-9007
Abstract

For more than 40 years, most astrophysical observations and laboratory studies of two key soft x-ray diagnostic 2p - 3d transitions, 3C and 3D, in Fe XVII ions found oscillator strength ratios f(3C)/f(3D) disagreeing with theory, but uncertainties had precluded definitive statements on this much studied conundrum. Here, we resonantly excite these lines using synchrotron radiation at PETRA III, and reach, at a millionfold lower photon intensities, a 10 times higher spectral resolution, and 3 times smaller uncertainty than earlier work. Our final result of f(3C)/f(3D) = 3.09(8)(6) supports many of the earlier clean astrophysical and laboratory observations, while departing by five sigmas from our own newest large-scale ab initio calculations, and excluding all proposed explanations, including those invoking nonlinear effects and population transfers.

DOI10.1103/PhysRevLett.124.225001