Janine Fleming

Systematic Studies of N IV Transitions of Astrophysical Importance

E1, M2, M1 and E2 rates of transitions between n = 2 levels of N IV have been calculated using the tw independent codes CIV3 and MCHF. Convergence of each of the approaches has been studied and comparisons made as the complexity of the calculations increases to include valence, core-valence and core-core correlation. The agreement between the two methods is sufficiently good to allow us to set quite narrow uncertainty bars. For the S-1-P-1 degrees resonance line, our recommended f-value is 0.609 with an estimated uncertainty of 0.002, while our recommended A-value for the S-1(0)-P-3(1) degrees intercombination line is 580 s(-1) with an estimated uncertainty of 10 s(-1).

The Bismuth Abundance in the HGMN Stars chi Lupi and HR 7775 and Improved Atomic Data for Selected Transitions of BI I, BI II, and BI III

High-resolution spectra of the chemically peculiar HgMn stars chi Lupiand HR 7775, obtained with the Hubble Space Telescope/Goddard HighResolution Spectrograph, are investigated for their abundance of bismuthby comparison with LTE synthetic spectrum modeling. HR 7775, previouslyknown from International Ultraviolet Explorer spectra to display stronglines of Bi II, is determined to have bismuth present at an enhancementlevel of nearly 5 orders of magnitude from the lines Bi IIlambdalambda1436, 1902 and Bi III lambda1423. The bismuthenhancement for chi Lupi is found to be near a level of 1.5 dex, andan ionization anomaly between Bi+ and Bi++ isapparent. HR 7775 abundance enhancements of the heavy elements platinum,[Pt/H]=4.7 dex, and gold, [Au/H]=3.8 dex, have also been determined. Newlaboratory measurements for wavelengths and hyperfine structure patternsof Bi I/Bi II/Bi III lines are presented, as well as the results ofcalculations for hyperfine structure constants and oscillator strengthsfor selected lines of Bi II and Bi III. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS5-26555. (Less)

The 1909 Å intercombination line in C III

The configuration interaction code CIV3 is used to calculate the A-value for the 1909 A 2s2 1S0-2s2p 3Po1 intercombination line in C III. An extensive calculation of valence shell correlation is augmented by the inclusion of core polarization effects both explicitly through further configurations with one or both 1s orbitals replaced by correlation orbitals, and also by the use of model potentials. Our recommended value of 104 ± 4s−1 for the A-value lies somewhat lower than the experimentally determined value of 121 ± 7s−1. We have estimated the expected error in our work by considering the extent of the convergence of our calculation. We also calculated the resonance transition and obtain an oscillator strength in excellent agreement with experiment.

Oscillator strengths for the resonance line of ions in the beryllium isoelectronic sequence

Extensive configuration-interaction calculations have been performed to obtain oscillator strengths for the resonance line of the ions of the beryllium isoelectronic sequence up to nuclear charge Z = 12. Valence, core-valence and core-core correlation effects are taken into account and relativistic effects are incorporated using the Breit-Pauli scheme. The present results are believed to be accurate to better than 1%.

3s23p–3s3p2 transitions in S iv

We use both the civ3 and mchf codes to calculate oscillator strengths of allowed and intercombination lines in the 3s(2) 3p-3s3p(2) multiplets. Valence, core-valence and some core-core correlation effects are included. The two approaches give results in excellent agreement. Core effects are particularly important for the intercombination lines, though relatively minor for allowed transitions. We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the transitions, compared with an experimental value of 1.12+/-0.1. The A -values of the intercombination lines are substantially different from those of previous calculations.

The - resonance line in neutral beryllium

The oscillator strength of the resonance transition - in neutral beryllium is evaluated using two independent codes: CIV3 and MCHF. Two separate approaches are executed using the code CIV3, which uses a common set of orbitals, the inclusion of valence, core - valence and core - core correlation being approached in different ways. In the MCHF scheme, the wavefunctions of the two states are optimized independently. The convergence of the MCHF results with respect to the addition of orbital functions is considered in some detail. This convergence, together with the results of the CIV3 calculations, lead us to recommend a value of 1.375 for the oscillator strength, with an estimated uncertainty of less than 0.5%. This agrees closely with other recent extensive calculations but is 2.5% higher than the value derived from beam-foil experiments.

A review of intercombination lines in beryllium-like ions

Theoretical and experimental results for the 2s2 1S0-2s2p3P1 intercombination line in beryllium-like ions are reviewed and revised, and some new data are presented. The uncertainty in the resulting transition rate is estimated, by using convergence of systematic calculations, accuracy of energy properties and theoretical tests, and is used to evaluate the accuracy of present and other calculations, and arrive at a recommended theoretical value, with uncertainty estimates.

The 2s22p3s 1,3PJo → 2s22p2 and 2s22p3p LSJ oscillator strengths in N II

A comparison between the recent measurements [Musielok et al, Phys. Rev. A53, 3122 (1996)] of the relative oscillator strengths for all lines in the three multiplets comprising the 2p3s-2p3p transition array in NII, and theoretical configuration interaction calculations performed with the CIV3 code [Bell et al., Physica Scripta 52 240 (1995)] shows that, although the agreement between the experimental data and the theoretical results is good for allowed transitions, some unexpected deviations occur for the intersystem lines. In this work, we show that the previous theoretical work can be improved and some significant discrepancies with experiment eliminated by increasing the accuracy of the calculated energy difference between the 2p3s 3P1o and 1P1o states. This is achieved by the inclusion of additional orbitals and configurations together with adjustment of the diagonal matrix elements of the Hamiltonian. The new theoretical results for the transitions 2p3s 1,3PJo → 2p2 and 2p3p LSJ are compared with other theoretical work and with the experimental data.

The 4s2 1S0 -4s4p 3P1o intercombination line in the zinc-like ions: Ga II, Kr VII, Sr IX, Nb XII, Mo XIII, Rh XVI and Ag XVIII

Transition probabilities are calculated for the 4s2 1S0 -4s4p 3P1o intercombination line in the zinc-like ions Ga II, Kr VII, Sr IX, Nb XII, Mo XIII, Rh XVI and Ag XVIII using the configuration interaction (CI) code CIV3. The calculation involves valence shell correlation, use of model potentials to account for core polarization and the inclusion of relativistic effects. Adjustments are made to the diagonal elements of the Hamiltonian matrix so that eigenvalue differences agree with experimental energy differences, so effectively experimental energies are used for transition energies and to refine the CI mixing coefficients of the wave functions. Both the A-values and the lifetimes of the transition for the various ions are compared with recent experimental and other theoretical results. The present results are sufficiently accurate to provide a benchmark for the analysis of the experimental data.

[O V] in the Ultraviolet Spectra of Gaseous Nebulae

Theoretical O V electron-density-sensitive emission line ratios for R = I(2s21S0 - 2s2p3P2)/I(2s21S0 - 2s2p3P1) are presented. Inspection of Goddard High Resolution Spectrograph Hubble Space Telescope spectra of RR Tel reveals the presence of the [O V] 2s21S - 2s2p3P2 line at 1213.80 A, which is 4.62 ± 0.12 A away from the 2s21S - 2s2p3P2 intercombination transition at 1218.42 A, in good agreement with the theoretical prediction of Δλ = 4.54 A. The resultant value of R = 0.82 ± 0.11 implies a logarithmic electron density, log Ne, of 5.2 ± 0.2 cm-3, in good agreement with that found from other ions with high electron temperature, such as Ne VI, which also provides support for the identification.