RADIATIVE L-SHELL TRANSITIONS IN Fe XIX AND Fe XX IONS

We compute the wavelengths and oscillator strengths for the 3s, 3d -> 2p, and 3p -> 2s emission lines in Fe XIX and Fe XX ions by using a configuration interaction Dirac-Fock and Dirac-Fock-Sturm method combined with second-order Brillouin-Wigner perturbation theory. We provide a complete list of computed wavelengths and oscillator strengths in both the velocity and length gauge for these transitions, many of which have never previously been reported. A comparison of our data with laboratory measurements and other theoretical predictions allows us to estimate an uncertainty of similar to 2 m angstrom in the wavelengths and an uncertainty of 2%-3% in the oscillator strengths. We expect that our calculations will provide a means of identifying emission lines from astrophysical sources and improve the ability to detect blending in X-ray grating spectra from Chandra and XMM-Newton. As an example, we present a simulated emission spectrum of Capella and find improved agreement between the observations and our calculations, compared with previous data sets.