Atomic data from the Iron Project XLV. Relativistic transition probabilities for carbon-like Ar XIII and Fe XXI using Breit-Pauli R-matrix method

The Breit-Pauli R-matrix method developed under the Iron Project has been used to obtain extensive sets of oscillator strengths and transition probabilities for dipole allowed and intercombination fine structure transitions in carbon like ions, Ar XIII and Fe XXI. The complete set consists of 1274 fine structure bound energy levels and 198,259 oscillator strengths for Ar XIII, and 1611 bound levels and 300,079 oscillator strengths for Fe XXI. These correspond to levels of total angular momenta of 0 <= J <= 7 of even and odd parities formed from total spin of 2S+1=5,3,1, and orbital angular momenta 0 <= L <= 9 with n <= 10, 0 <= l <= 9 for each ion. The relativistic effects are included in the Breit-Pauli approximation. The close coupling wavefunction expansion for each ion is represented by the lowest 15 fine structure levels of target configuations, 2s2.2p, 2s.2p2 and 2p3. The energy levels are identified spectroscopically using a newly developed identification procedure. The procedure also makes a correspondence between the fine strucure energy levels and LS terms. This provides the check for completeness of the calculated levels. Comparison is made of the present energies and the f-values with the available observed and theoretical values. Present transition probabilitis agree very well with the relativistic atomic structure calculations of Mendoza et al. for the intercombination transitions, 2s.2p3(5So)2 - 2s2.2p2(3P){1,2},(1D)2. This further indicates that the importance of the neglected Breit interaction decreases with ion charge and constrains the uncertainty in the present calculations to within 15% even for the weak transitions.Comment: Submitted to AA Sup

Electron-Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. VII. Relativistic calculations for O VI and O VII for UV and X-ray modeling

Aimed at ionization balance and spectral analysis of UV and X-ray sources, we present self-consistent sets of photoionization cross sections, recombination cross sections, and rate coefficients for Li-like O VI and He-like O VII. Relativistic fine structure is considered through the Breit-Pauli R-matrix (BPRM) method in the close coupling approximation, implementing the unified treatment for total electron-ion recombination subsuming both radiative and di-electronic recombination processes. Self-consistency is ensured by using an identical wavefunction expansion for the inverse processes of photoionization and photo-recombination. Radiation damping of resonances, important for H-like and He-like core ions, is included. Compared to previous LS coupling results without radiative decay of low-n (<= 10) resonances, the presents results show significant reduction in O VI recombination rates at high temperatures. In addition to the total rates, level-specific photoionization cross sections and recombination rates are presented for all fine structure levels n (lSLJ) up to n <= 10, to enable accurate computation of recombination-cascade matrices and spectral formation of prominent UV and X-ray lines such as the 1032,1038 A doublet of O VI, and the `triplet' forbidden, intercombination, and resonance X-ray lines of O VII at 22.1, 21.8, and 21.6 \ang respectively. Altogether, atomic parameters for 98 levels of O VI and 116 fine structure levels of O VII are theoretically computed. These data should provide a reasonably complete set of photoionization and recombination rates in collisional or radiative equilibrium.Comment: 33 pages, 8 figures, submitted to ApJ