New atomic data for Ge XX

We have performed large-scale configuration interaction (CI) calculations using CIV3for the lowest (in energy) 155 fine-structure levels of aluminum-like germanium ion. We have calculated the energy levels, lifetimes, oscillator strengths, and transition probabilities for the electric-dipole allowed and intercombination transitions among the levels of ground state3s23p(2P)and higher energy levels of states3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2,3p3d2, 3d3,3s2(4s, 4p, 4d, 4f) ofGe XX in the LSJ coupling scheme.The present results include relativistic effects through the Breit-Pauli operator. In order to keep our calculated energy splittings as close as possible to the experimental and theoretical results complied by NIST, we attempt to correct the inaccuracies in the CI coefficients in the wavefunctions, which would lead to inaccuracies in transition probabilities, by applying a "fine-tuning" technique. Fine-tuning of the ab initio energies was donethrough adjusting, by a small amount, some diagonal elements of the Hamiltonian matrix.Comparisons are made with other available experimental and theoretical results and the accuracy of the present results is assessed.Comment: Supplemental Archive Journal-ref: Journal of Quantitative Spectroscopy and Radiative Transfer JQSRT-D-15-0010

Assessment of atomic data: problems and solutions

For the reliable analysis and modelling of astrophysical, laser-produced and fusion plasmas, atomic data are required for a number of parameters, including energy levels, radiative rates and electron impact excitation rates. Such data are desired for a range of elements (H to W) and their many ions. However, measurements of atomic data, mainly for radiative and excitation rates, are not feasible for many species and therefore calculations are needed. For some ions (such as of C, Fe and Kr) there are a variety of calculations available in the literature, but often they significantly differ from one another. Therefore, there is a great demand from the user community to have data `assessed' for accuracy so that they can be confidently applied to the modelling of plasmas. In this paper we highlight the difficulties in assessing atomic data and offer some solutions for improving the accuracy of calculated results.Comment: 17 pages of Text only with 60 References - to be published in FS&T (2013

The Belgian repository of fundamental atomic data and stellar spectra (BRASS). I. Cross-matching atomic databases of astrophysical interest

Fundamental atomic parameters, such as oscillator strengths, play a key role in modelling and understanding the chemical composition of stars in the universe. Despite the significant work underway to produce these parameters for many astrophysically important ions, uncertainties in these parameters remain large and can propagate throughout the entire field of astronomy. The Belgian repository of fundamental atomic data and stellar spectra (BRASS) aims to provide the largest systematic and homogeneous quality assessment of atomic data to date in terms of wavelength, atomic and stellar parameter coverage. To prepare for it, we first compiled multiple literature occurrences of many individual atomic transitions, from several atomic databases of astrophysical interest, and assessed their agreement. Several atomic repositories were searched and their data retrieved and formatted in a consistent manner. Data entries from all repositories were cross-matched against our initial BRASS atomic line list to find multiple occurrences of the same transition. Where possible we used a non-parametric cross-match depending only on electronic configurations and total angular momentum values. We also checked for duplicate entries of the same physical transition, within each retrieved repository, using the non-parametric cross-match. We report the cross-matched transitions for each repository and compare their fundamental atomic parameters. We find differences in log(gf) values of up to 2 dex or more. We also find and report that ~2% of our line list and Vienna Atomic Line Database retrievals are composed of duplicate transitions. Finally we provide a number of examples of atomic spectral lines with different log(gf) values, and discuss the impact of these uncertain log(gf) values on quantitative spectroscopy. All cross-matched atomic data and duplicate transitions are available to download at brass.sdf.org.Comment: 18 pages, 12 figures, 9 tables. Accepted for publication in A&

Atomic Processes in Planetary Nebulae and H II Regions

Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have driven much development in atomic physics. In the last few years the combination of a generation of powerful observatories, the development of ever more sophisticated spectral modeling codes, and large efforts on mass production of high quality atomic data have led to important progress in our understanding of the atomic spectra of such astronomical objects. In this paper I review such progress, including evaluations of atomic data by comparisons with nebular spectra, detection of spectral lines from most iron-peak elements and n-capture elements, observations of hyperfine emission lines and analysis of isotopic abundances, fluorescent processes, and new techniques for diagnosing physical conditions based on recombination spectra. The review is directed toward atomic physicists and spectroscopists trying to establish the current status of the atomic data and models and to know the main standing issues.Comment: 9 pages, 1 figur

State- and event-based refinement

In this paper we give simple example abstract data types, with atomic operations, that are related by data refinement under a definition used widely in the literature, but these abstract data types are not related by singleton failure refinement. This contradicts results found in the literature. Further we show that a common way to change a model of atomic operations to one of value passing operations actually changes the underlying atomic operational semantics