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- ID:
- ivo://CDS.VizieR/J/ApJS/234/27
- Title:
- FeXIX-XXV recombination lines
- Short Name:
- J/ApJS/234/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a systematic measurement of the X-ray emission asymmetries in the K-shell dielectronic, trielectronic, and quadruelectronic recombination of free electrons into highly charged ions. Iron ions in He-like through O-like charge states were produced in an electron beam ion trap, and the electron-ion collision energy was scanned over the recombination resonances. Two identical X-ray detectors mounted head-on and side-on with respect to the electron beam propagation recorded X-rays emitted in the decay of resonantly populated states. The degrees of linear polarization of X-rays inferred from observed emission asymmetries benchmark distorted-wave predictions of the Flexible Atomic Code for several dielectronic recombination satellite lines. The present method also demonstrates its applicability for diagnostics of energy and direction of electron beams inside hot anisotropic plasmas. Both experimental and theoretical data can be used for modeling of hot astrophysical and fusion plasmas.
263. FeX soft X-ray lines
- ID:
- ivo://CDS.VizieR/J/A+A/541/A90
- Title:
- FeX soft X-ray lines
- Short Name:
- J/A+A/541/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New atomic calculations for Fe X are presented. They focus on the need to model the soft X-ray spectrum and in particular the line at 94.0{AA} which is the dominant contribution to the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94{AA} band in quiet Sun conditions. This line, and others in the band, are due to strong decays from n=4 levels. We present new large-scale R-matrix (up to n=4) and distorted-wave (DW, up to n=6) scattering calculations for electron collisional excitation and compare them to earlier work. We find significant discrepancies with previous calculations. We show that resonances significantly increase the cross-sections for excitations from the ground state to some n=4 levels, in particular to those in the 3s^2^ 3p^4^ 4s configuration. Cascading from higher levels is also important. We suggest a new identification for the 3s 3p^6^ ^2^S_1/2_ - 3s 3p^5^ 4s ^2^P_3/2_ transition, that has a predicted intensity larger than the decays from the 3s^2^ 3p^4^ 4s levels which were identified by Edlen in 1936. The results presented here are relevant to our understanding of transitions from n=4 levels in a wide range of other ions.
- ID:
- ivo://CDS.VizieR/J/A+A/459/307
- Title:
- Fe XVIII Benchmarking atomic data
- Short Name:
- J/A+A/459/307
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fe XVIII produces, in the X-ray and extreme ultraviolet, L-shell (n=2,3,4->2) spectral lines which are among the brightest ones in e.g. solar flares and in Chandra, XMM-Newton spectra of active stars. Recent R-matrix scattering calculations of Witthoeft et al. (2006A&A...446..361W) produce theoretical intensities for some of the brightest transitions increased by large factors (2-3), so it is timely to use these calculations to review and assess all previous line identifications on a quantitative basis. This paper discusses only the most important lines for laboratory and astrophysical applications. Many previous identifications are revised and some tentative ones finally confirmed. Many lines are found to be significantly blended. A considerable number of new identifications are proposed. Excellent agreement between observed and predicted intensities is found in the majority of cases for the first time. It is therefore now possible to use Fe XVIII L-shell lines to measure electron densities in laboratory plasmas and temperatures for a wide range of astrophysical sources.
- ID:
- ivo://CDS.VizieR/J/A+A/418/1171
- Title:
- FeXVIII-FeXXIII effective collision strengths
- Short Name:
- J/A+A/418/1171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoabsorption cross sections across the K edge of Fe XVIII-Fe XXIII and electron impact K-shell excitation effective collision strengths in Fe XVIII-Fe XXIII have been computed with the Breit-Pauli R-matrix method. The target models are represented with all the fine-structure levels within the n=2 complex, built up from single-electron orbital bases obtained in a Thomas-Fermi-Dirac statistical model potential. The effects of radiation and spectator Auger dampings are taken into account by means of an optical potential. In photoabsorption, these effects cause the resonances converging to the K thresholds to display symmetric profiles of constant width that smear the edge, with important implications in spectral analysis. In collisional excitation, they attenuate resonances making their contributions to the effective collision strength practically negligible.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A83
- Title:
- FeXVII-XXV K lines Plasma environment effects
- Short Name:
- J/A+A/626/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the context of accretion disks around black holes, we estimate plasma-environment effects on the atomic parameters associated with the decay of K-vacancy states in highly charged iron ions, namely FeXVII-FeXXV. Within the relativistic multiconfiguration Dirac-Fock (MCDF) framework, the electron-nucleus and electron-electron plasma screenings are approximated with a time-averaged Debye-Huckel potential. Modified ionization potentials, K thresholds, wavelengths, radiative emission rates and Auger widths are reported for astrophysical plasmas characterized by electron temperatures and densities respectively in the ranges 10^5^-10^7^K and 10^18^-10^22^cm^-3^. We conclude that the high-resolution micro-calorimeters onboard future X-ray missions such as XRISM and ATHENA are expected to be sensitive to the lowering of the iron K edge due to the extreme plasma conditions occurring in accretion disks around compact objects.
- ID:
- ivo://CDS.VizieR/J/A+A/450/1249
- Title:
- Fe XVI radiative and excitation rates
- Short Name:
- J/A+A/450/1249
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we report calculations for energy levels, radiative rates, collision strengths, and effective collision strengths for transitions in Fe XVI. For energy levels and radiative rates we have used the General purpose Relativistic Atomic Structure Package (GRASP), and for the computations of collision strengths the Dirac Atomic R-matrix Code (DARC) has been adopted. Energies for the lowest 39 levels among the n<=7 (l<=4) configurations of Fe XVI are reported. Additionally, radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Electron impact excitation collision strengths have also been calculated for all 741 transitions among the above 39 levels over a wide energy range up to 220 Ryd. Resonances have been resolved in the threshold region, and effective collision strengths have been obtained over a wide temperature range up to 10^7^K. Comparisons are made with the available results in the literature, and the accuracy of the present results is assessed.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/11
- Title:
- Fe XVI radiative rates
- Short Name:
- J/ApJS/207/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate theoretical energy level, lifetime, and transition probability calculations of core-excited Fe XVI were performed employing the relativistic Multireference Moller-Plesset perturbation theory. In these computations the term energies of the highly excited n<=5 states arising from the configuration 1s^2^2s^k^2p^m^3l^p^nl'^q^, where k+m+p+q=9, l<=3 and p+q<=2 are considered, including those of the autoionizing levels with a hole-state in the L-shell. All even and odd parity states of sodium-like iron ion were included for a total of 1784 levels. Comparison of the calculated L-shell transition wavelengths with those from laboratory measurements shows excellent agreement. Therefore, our calculation may be used to predict the wavelengths of as of yet unobserved Fe XVI, such as the second strongest 2p-3d Fe XVI line, which has not been directly observed in the laboratory and which blends with one of the prominent Fe XVII lines.
- ID:
- ivo://CDS.VizieR/J/A+A/463/399
- Title:
- Fe XVI radiative rates
- Short Name:
- J/A+A/463/399
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we report calculations for energy levels and radiative rates for transitions in Fe XVI. The General purpose Relativistic Atomic Structure Package GRASP has been adopted for the calculations of energy levels and radiative rates. Energies for the lowest 134 levels among the (1s^2^2s^2^) 2p^6^3l, 2p^5^3s^2^, 2p^5^3s3p, 2p^5^3s3d, 2p^5^3p3d, and 2p^5^3p^2^ configurations of Fe XVI are reported. Additionally, radiative rates, oscillator strengths, and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), magnetic quadrupole (M2), and electric octupole (E3) transitions among these levels. Comparisons are made with the available results in the literature, and the accuracy of the present results is assessed. Finally, lifetimes for all excited levels are also listed, although no measurements are presently available with which to compare these.
- ID:
- ivo://CDS.VizieR/J/A+A/433/745
- Title:
- FeXX energy levels + transition probabilities
- Short Name:
- J/A+A/433/745
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Energy levels and the corresponding transition probabilities as well as oscillator strengths and line strengths for allowed (E1) and forbidden (E2, M1) transitions among the lowest 700 levels of nitrogen-like Fe XX are presented. Calculations were performed using the multiconfigurational Dirac-Fock GRASP code.
