Parts | Days | Selection | Search | Downloads | Help
A: Atomphysik
A 19: Symposium Hochgeladene Ionen III
A 19.4: Talk
Friday, March 19, 1999, 17:30–17:45, TE1
Ion Storage Ring Measurements of Dielectronic Recombination for Astrophysically Important Feq+ Ions — •D. W. Savin1, T. Bartsch2, C. Brandau2, G. Gwinner3, A. Hoff"-knecht2, J. Linkemann3, A. M"uller2, A. A Saghiri3, S. Schippers2, M. Schmitt3, D. Schwalm3, A. Wolf3, S. M. Kahn1, M. H. Chen4, and N. R. Badnell5 — 1Astrophysics Lab., Columbia Univ., New York, USA — 2Univ. Gie"sen — 3Max-Planck-Institut f"ur Kernphysik, Heidelberg und Phys. Inst. der Univ. Heidelberg — 4Lawrence Livermore National Lab., USA — 5Univ. of Strathclyde, Glasgow, U.K.
Feq+ ions provide many valuable diagnostics for cosmic plasmas, whose accuracy often depends on a good understanding of dielectronic recombination (DR). Using the heavy-ion storage ring TSR at the MPI for Nuclear Physics in Heidelberg we have measured the Δ n=0 DR rate for Fe17+ [1] and Fe18+. These rates are important for photoionized gases such as are found in active galactic nuclei, X-ray binaries, and cataclysmic variables. We find that the DR rates at temperatures below ≈20 eV are dominated by resonances involving fine-structure excitations of the 2p5 2P or 2p4 3P core, resp., and are underestimated by existing theoretical DR rates, mostly not including these excitations. For Fe18+ the existing theoretical DR rates exceed the experiment by a factor of up to 2 above ≈100 eV, possibly because autoionization into fine-structure excited states of the 2p4 3P core should be included in addition. Similar discrepancies may be expected for most ions with partially filled p or d shells. New calculations have been carried out and agree with experiment to within ∼ 30%. — Supported in part by NASA, NATO, and the German BMBF.
[1] D. W. Savin et al., Astrophys. J. Lett. 489, L115 (1997)