High-temperature behaviour of the helium-like Kα G ratio: the effect of improved recombination rate coefficients for calcium, iron and nickel

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Abstract

It is shown that above the temperature of maximum abundance, recombination rates into the excited states of He-like ions that are calculated using earlier, more approximate methods differ markedly from rates obtained from recent distorted-wave and R-matrix calculations (unified recombination rate coefficients) for Ca, Fe and Ni. The present rates lead to G ratios that are greatly lower than those resulting from the more approximate rates in previous works, by up to a factor of 6 at high electron temperatures. Excellent agreement between the distorted-wave and the R-matrix rates, as well as excellent agreement in the G ratios calculated from them, provides support for the accuracy of these new values which have a broad applicability to the modelling and interpreting of X-ray spectra from a variety of astrophysical and laboratory sources.

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Relevant data is available at: http://www.astronomy.ohio-state.edu/~nahar/nahar_radiativeatomicdata/index.html
The definitive version is available at www.blackwell-synergy.com. http://www3.interscience.wiley.com/journal/117975880/abstract

Keywords

atomic data, atomic processes, line -- formation, X-rays -- general

Citation

Oelgoetz, J., Fontes, C. J., Zhang, H. L., Montenegro, M., Nahar, Sultana Nurun, Pradhan, A. K. "High-temperature behaviour of the helium-like Kα G ratio: the effect of improved recombination rate coefficients for calcium, iron and nickel," Monthly Notices of the Royal Astronomical Society, v. 382, no. 2, 2007, pp. 761-769.