Heidelberg 1999 – scientific programme

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 Fe^q+ 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.

Fe^q+ 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 2p^5 2P or 2p^4 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 2p^4 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)