Breit–Pauli R-matrix calculations for electron impact excitation of Fe XVII: a benchmark study
TL;DR: In this article, low-energy electron impact excitation of Ne-like Fe16+ with emphasis on relativistic and resonance effects using a Breit-Pauli R-matrix code was studied.
Abstract: We have studied low-energy electron impact excitation of Ne-like Fe16+ with emphasis on relativistic and resonance effects using a Breit–Pauli R-matrix code. Processes with one electron excited into the M shell, i.e. involving the closed-shell ground state and 36 more fine-structure levels (37CC), are compared with those from a target extended to the N shell (n = 4, 89CC—CC indicating a close coupling approach to a partial wave expansion). In contrast to previous work the 37CC and the 89CC collision strengths exhibit far richer structure. All N-shell levels give rise to Rydberg resonant states dipping right to all M-shell thresholds. This will modify all 37CC collision strengths down to every excitation threshold, not merely over the extended target energy range, thus significantly affecting the collision strengths for the primary x-ray and EUV transitions among the first 37 levels. Extensive study of other effects on the collision strength is also reported: (i) electric and magnetic multipole type transitions E1, E2, E3 and M1, M2, (ii) J-partial wave convergence of dipole and non-dipole transitions, (iii) high-energy behaviour compared to other approximations. Theoretical results are benchmarked against experiment to resolve long-standing discrepancies—collision strengths for the three prominent x-ray lines 3C, 3D and 3E at 15.015, 15.262 and 15.450 A are in good agreement with two independent measurements on electron beam ion traps (EBITs). Finally, line ratios from a collisional–radiative model using the new collisional rates are compared with observations from stellar coronae and EBITs to illustrate potential applications in laboratory and astrophysical plasmas.
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TL;DR: The available atomic data used for interpreting and modeling x-ray observations can be divided into several levels of detail, ranging from compilations which can be used with direct inspection of raw data, such as line finding lists, to synthetic spectra which attempt to fit to an entire observed dataset simultaneously as mentioned in this paper.
Abstract: The available atomic data used for interpreting and modeling x-ray observations are reviewed The applications for these data can be divided into several levels of detail, ranging from compilations which can be used with direct inspection of raw data, such as line finding lists, to synthetic spectra which attempt to fit to an entire observed dataset simultaneously This review covers cosmic sources driven by both electron ionization and photoionization and touches briefly on planetary surfaces and atmospheres The applications to x-ray astronomy, the available data, and recommendations for astronomical users are all reviewed, and an attempt to point out the applications where the shortcomings are greatest is also given
101 citations
TL;DR: In this paper, the authors present complete collisional-radiative modelling results for the soft x-ray emission lines of Fe16+ in the 15 A-17 A range.
Abstract: We present complete collisional-radiative modelling results for the soft x-ray emission lines of Fe16+ in the 15 A–17 A range. These lines have been the subject of much controversy in the astrophysical and laboratory plasma community. Radiative transition rates are generated from fully relativistic atomic structure calculations. Electron-impact excitation cross sections are determined using a fully relativistic R-matrix method employing 139 coupled atomic levels through n = 5. We find that, in all cases, using a simple ratio of the collisional rate coefficient times a radiative branching factor is not sufficient to model the widely used diagnostic line ratios. One has to include the effects of collisional-radiative cascades in a population model to achieve accurate line ratios. Our line ratio results agree well with several previous calculations and reasonably well with tokamak experimental measurements, assuming a Maxwellian electron-energy distribution. Our modelling results for four EBIT line ratios, assuming a narrow Gaussian electron-energy distribution, are in generally poor agreement with all four NIST measurements but are in better agreement with the two LLNL measurements. These results suggest the need for an investigation of the theoretical polarization calculations that are required to interpret the EBIT line ratio measurements.
68 citations
TL;DR: In this article, the electron-impact excitation of all Ne-like ions from Na + to Kr 26+ obtained using the intermediate-coupling frame transformation R-matrix approach.
Abstract: We present results for the electron-impact excitation of all Ne-like ions from Na + to Kr 26+ obtained using the intermediate-coupling frame transformation R-matrix approach. For each ion’s calculation, the close-coupling expansion is taken to be the 113 LS terms (209 levels) belonging to the configurations [1s 2 ]2s 2 2p 6 ,2 s 2 2p 5 {3, 4, 5}l ,2 s2p 6 {3, 4, 5}l (l ∈ s, p, d, f, and g), and 2s 2 2p 5 {6, 7}l � (l � ∈ s, p, and d). An additional configuration interaction effect arising from configurations of 2s 2 2p 4 3l{3, 4, 5}l �� (l �� ∈ s, p, d, f and g) was included in the target expansion. A detailed comparison of the target structure has been made for six specific ions (Si 4+ ,A r 8+ ,C a 10+ ,
67 citations
TL;DR: In this paper, an extensive set of fine structure levels and corresponding transition probabilities for allowed and forbidden transitions in Fe xvii were presented, which translate to over $2.6 × 10^4$ allowed (E1) transitions that are of dipole and intercombination type, and over $2312 forbidden transitions that include electric quadrupole(E2), magnetic dipole (M1), electric octopole (E3), and magnetic quadrupoles (M2) type.
Abstract: An extensive set of fine structure levels and corresponding transition probabilities for allowed and forbidden transitions in Fe xvii is presented. A total of 490 bound energy levels of Fe xvii of total angular momenta $0 \leq J \leq 7$ of even and odd parities with $2 \leq n\leq 10$, $0 \leq l\leq 8$, $0 \leq L\leq 8$, and singlet and triplet multiplicities, are obtained. They translate to over $2.6\times 10^4$ allowed (E1) transitions that are of dipole and intercombination type, and 2312 forbidden transitions that include electric quadrupole (E2), magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type representing the most detailed calculations to date for the ion. Oscillator strengths f , line strengths S , and coefficients A of spontaneous emission for the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix approximation. A -values for the forbidden transitions are obtained from atomic structure calculations using codes SUPERSTRUCTURE and GRASP. The energy levels are identified in spectroscopic notation with the help of a newly developed level identification algorithm. Nearly all 52 spectroscopically observed levels have been identified, their binding energies agreeing within 1% with our calculation. Computed transition probabilities are compared with other calculations and measurement. The effect of 2-body magnetic terms and other interactions is discussed. The present data set enhances by more than an order of magnitude the heretofore available data for transition probabilities of Fe xvii.
57 citations
TL;DR: In this paper, the authors compare R-matrix scattering calculations for electron impact excitation of Fe xvii with various X-ray solar observations, and show that the difference between the expected and measured line intensities is within 10% with the exception of a few weaker lines that appear to be blended, without the need to invoke opacity effects in the stronger line.
Abstract: Recent R-matrix scattering calculations for electron impact excitation of Fe xvii are benchmarked against various X-ray solar observations. Quiescent active region observations are considered, together with a few SMM/FCS observations of active regions and flares analysed here. Extremely good agreement (within 10%) between expected and measured line intensities is found, with the exception of a few weaker lines that appear to be blended, and without the need to invoke opacity effects in the stronger line. The long-standing discrepancies that have been present when distorted wave (DW) calculations are adopted are now finally resolved. As was shown in the Fe xviii case, the differences with the DW calculations are caused by resonances that significantly increase the collision strengths of the 2p‐3s transitions. The strong Fe xvii lines can now be reliably used to measure electron temperatures in the solar corona and other astrophysical sources. Emission measure modelling with the most recent atomic data of quiescent active region cores indicates O/Fe and Ne/Fe abundances reduced by factors of two to four compared to the latest compilation of “photospheric” abundances.
46 citations
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TL;DR: The Oxford MCP/MCDF and MCBP/BENA packages have been rewritten in FORTRAN 77 and combined in the new code, GRASP, which is more versatile than its predecessors, contains more stable and accurate numerical procedures and a simplified but more flexible interface.
1,188 citations
TL;DR: In this paper, a suite of programs for multiconfiguration or configuration-interaction relativistic atomic structure calculations with large configuration state function lists is described, where atomic orbitals are taken to be four-component spinors.
800 citations
TL;DR: Superstructure as mentioned in this paper is a general-purpose automatic atomic-structure program that uses multi-configuration type expansions to calculate term energies, intermediate-coupling energy levels, term coupling coefficients, and cascade coefficients.
781 citations
TL;DR: RMATRX1 as mentioned in this paper is a general program to calculate atomic continuum processes using the R -matrix method, including electronatom and electron-ion scattering, and radiative processes such as bound-bound transitions, photoionization and polarizabilities.
679 citations
TL;DR: The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton observatory in February 2000 as its first-light target, and a total of 570 ks of exposure time was accumulated with the Reflection Grating Spectrometers (RGS).
Abstract: The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton observatory in February 2000 as its first-light target A total of 570 ks of exposure time was accumulated with the Reflection Grating Spectrometers (RGS) The integrated X-ray spectrum between 5-38A is of unprecedented quality and shows numerous features attributed to transitions of the elements C, N, O, Ne, Mg, Si, S, Fe Ni, and probably others We perform an in-depth study of the elemental composition of the average corona of this system, and find that the elemental abundances strongly depend on the first ionisation potential (FIP) of the elements But different from the solar coronal case, we find an inverse FIP effect, ie, the abundances (relative to oxygen) increase with increasing FIP Possible scenarios, eg, selective enrichment due to Ne-rich flare-like events, are discussed
197 citations