Picture of UK Houses of Parliament

Leading national thinking on politics, government & public policy through Open Access research

Strathprints makes available scholarly Open Access content by researchers in the School of Government & Public Policy, based within the Faculty of Humanities & Social Sciences.

Research here is 1st in Scotland for research intensity and spans a wide range of domains. The Department of Politics demonstrates expertise in understanding parties, elections and public opinion, with additional emphases on political economy, institutions and international relations. This international angle is reflected in the European Policies Research Centre (EPRC) which conducts comparative research on public policy. Meanwhile, the Centre for Energy Policy provides independent expertise on energy, working across multidisciplinary groups to shape policy for a low carbon economy.

Explore the Open Access research of the School of Government & Public Policy. Or explore all of Strathclyde's Open Access research...

Dielectronic recombination in photoionized gas. II. Laboratory measurements for Fe xviii and Fe xix

Savin, D.W. and Kahn, S.M. and Linkemann, J. and Saghiri, A.A. and Schmitt, M. and Grieser, M. and Repnow, R. and Schwalm, D. and Wolf, A. and Bartsch, T. and Brandau, C. and Hoffknecht, A. and Müller, A. and Schippers, S. and Chen, M.H. and Badnell, N.R. (1999) Dielectronic recombination in photoionized gas. II. Laboratory measurements for Fe xviii and Fe xix. Astrophysical Journal, 123 (2). pp. 687-702. ISSN 0004-637X

[img]
Preview
Text (strathprints005827)
strathprints005827.pdf
Accepted Author Manuscript

Download (660kB)| Preview

    Abstract

    In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj → nl′j′ core excitations (n = 0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII n = 0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX n = 0 DR rate coefficients. Significant discrepancies exist between our inferred rates and those of published calculations. These calculations overestimate the DR rates by factors of ∼ 2 or underestimate it by factors of ∼ 2 to orders of magnitude, but none are in good agreement with our results. Almost all published DR rates for modeling cosmic plasmas are computed using the same theoretical techniques as the above-mentioned calculations. Hence, our measurements call into question all theoretical n = 0 DR rates used for ionization balance calculations of cosmic plasmas. At temperatures where the Fe XVIII and Fe XIX fractional abundances are predicted to peak in photoionized gases of cosmic abundances, the theoretical rates underestimate the Fe - 2 - XVIII DR rate by a factor of ∼ 2 and overestimate the Fe XIX DR rate by a factor of ∼ 1.6. We have carried out new multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli calculations which agree with our measured resonance strengths and rate coefficients to within typically better than ∼ < 30%. We provide a fit to our inferred rate coefficients for use in plasma modeling. Using our DR measurements, we infer a factor of ∼ 2 error in the Fe XX through Fe XXIV n = 0 DR rates. We investigate the effects of this estimated error for the well-known thermal instability of photoionized gas. We find that errors in these rates cannot remove the instability, but they do dramatically affect the range in parameter space over which it forms.