Dielectronic satellite spectra of heliumlike iron and nickel from the unified recombination method

Abstract

It is shown that resonances in the unified recombination cross sections correspond directly to dielectronic satellite spectra. Positions, intensities, and profiles of satellite lines may be obtained accurately using the Breit-Pauli $R$-matrix method and the unified theory of total electron-ion recombination. The intrinsic dielectronic resonance strength corresponding to autoionizing resonances is defined in analogy with measured quantities, and with resonance oscillator strengths. Satellite intensities then depend extrinsically on dynamical parameters in the plasma and may be obtained at any temperature in a straightforward manner from the resonance strengths. Profiles of dielectronic satellite lines of He-like $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}\mathrm{XXV}$ and $\mathrm{Ni}\phantom{\rule{0.2em}{0ex}}\mathrm{XXVII}$ are obtained in an ab initio manner. Detailed calculations also exhibit interference effects in resonance profiles delineated at high resolution. Although interference among resonances is not important for resonance strengths of the highly charged ions $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}\mathrm{XXV}$ and $\mathrm{Ni}\phantom{\rule{0.2em}{0ex}}\mathrm{XXVII}$ it might be significant for lower ionization states of heavy elements in general. The resonance identitification scheme for unified recombination cross sections is described, and applied to obtain all known $KLL$ satellites of $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}\mathrm{XXV}$ and $\mathrm{Ni}\phantom{\rule{0.2em}{0ex}}\mathrm{XXVII}$. Dielectronic satellite strengths are compared with earlier works and significant differences and similarities are discussed.