Abstract
Understanding the Fe
II
emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving ...both quasar classification schemes such as “Eigenvector 1” and tracing the chemical evolution of the cosmos. Recently, three large Fe
II
atomic data sets with radiative and electron collisional rates have become available. We have incorporated these into the spectral synthesis code
Cloudy
and examined predictions using a new generation of AGN spectral energy distribution (SED), which indicates that the ultraviolet (UV) emission can be quite different depending on the data set utilized. The Smyth et al. data set better reproduces the observed Fe
II
template of the I ZW 1 Seyfert galaxy in the UV and optical regions, and we adopt these data. We consider both thermal and microturbulent clouds and show that a microturbulence of ≈100 km s
−1
reproduces the observed shape and strength of the so-called Fe
II
“UV bump.” Comparing our predictions to the observed Fe
II
template, we derive a typical cloud density of 10
11
cm
−3
and photon flux of 10
20
cm
−2
s
−1
, and show that these largely reproduce the observed Fe
II
emission in the UV and optical. We calculate the
I
(Fe
II
)/
I
(Mg
II
) emission-line intensity ratio using our best-fitting model and obtain log(
I
(Fe
II
)/
I
(Mg
II
)) ∼ 0.7, suggesting many AGNs have a roughly solar Fe/Mg abundance ratio. Finally, we vary the Eddington ratio and SED shape as a step in understanding the Eigenvector 1 correlation.
A selection of electron-impact excitation
R
-matrix calculations completed by the collision group at Queens University Belfast are discussed. The atomic data calculated are the foundation of ...applications in a variety of fields, a sample of which are presented here. They include an analysis of Fe
ii
emission in active galactic nuclei, the possible presence of Pt and Au in the spectra of binary neutron star mergers and the viability of W ions as a diagnostic tool in magnetically confined tokamak plasmas. The radiative atomic data were computed using the most recent version of the fully relativistic structure code
grasp0
and the collision cross sections were evaluated using the recently developed
pdarc
R
-matrix package.
Graphic abstract
ABSTRACT
Energy levels, Einstein A-values, and oscillator strengths are calculated for doubly ionized germanium (Ge iii). We have undertaken a study of the electron-impact excitation of Ge iii and ...have also completed a study of the photoionization of Ge ii. Ge iii target structures were generated using the relativistic grasp0 package. Several scattering models were investigated to assess the uncertainty quantification of our results. Initially, the lowest lying 64 jj fine-structure levels were included in the close-coupling expansion resulting from 14 non-relativistic configurations. A second larger model was subsequently generated using the gasp package and incorporated the lowest 589 jj fine-structure levels from 17 non-relativistic configurations. Both the DARC (Dirac atomic R-matrix code) and Breit–Pauli parallel suite of R-matrix collision codes were utilized in the scattering calculations to generate the collision strengths for incident electron energies between 0 and 5 Rydbergs and subsequently the Maxwellian-averaged effective collision strengths for temperatures in the range of 1000–200 000 K. The photoionization calculations comprised of two studies, a DARC and a Breit–Pauli calculation incorporating the 250 lowest lying levels. Photoionization cross-sections for Ge ii are presented in the range of 0–5 Ryds. Due to the lack of data available in the literature, the present radiative data and electron-impact/photoionization cross-sections are compared between the models presented in this paper. To assess their significance for astrophysics, the data are incorporated into the stellar atmosphere package sterne. Test models for the heavy-metal subdwarf LS IV−14○116 are not affected by the new data, but models for cooler stars may be sensitive to them.
ABSTRACT
We extend the range of validity of the artis 3D radiative transfer code up to hundreds of days after explosion, when Type Ia supernovae (SNe Ia) are in their nebular phase. To achieve this, ...we add a non-local thermodynamic equilibrium population and ionization solver, a new multifrequency radiation field model, and a new atomic data set with forbidden transitions. We treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionization, and heating. We validate our method with a variety of tests including comparing our synthetic nebular spectra for the well-known one-dimensional W7 model with the results of other studies. As an illustrative application of the code, we present synthetic nebular spectra for the detonation of a sub-Chandrasekhar white dwarf (WD) in which the possible effects of gravitational settling of 22Ne prior to explosion have been explored. Specifically, we compare synthetic nebular spectra for a 1.06 M⊙ WD model obtained when 5.5 Gyr of very efficient settling is assumed to a similar model without settling. We find that this degree of 22Ne settling has only a modest effect on the resulting nebular spectra due to increased 58Ni abundance. Due to the high ionization in sub-Chandrasekhar models, the nebular Ni ii emission remains negligible, while the Ni iii line strengths are increased and the overall ionization balance is slightly lowered in the model with 22Ne settling. In common with previous studies of sub-Chandrasekhar models at nebular epochs, these models overproduce Fe iii emission relative to Fe ii in comparison to observations of normal SNe Ia.
Significant contributions to the UV opacity in the solar atmosphere have been found to stem from bound-free transitions in neutral iron. As such, accurate cross sections for the photoionisation ...process are required for a detailed and meaningful analysis. However, existing photoionisation cross sections display large discrepancies across the low-energy region, highlighting the need for further calculations. In this work, we present level-resolved photoionisation cross sections for neutral iron across a wide energy range from a 262 level Dirac R-matrix calculation. Comparisons with existing experimental measurements reveal good agreement in the positions of the various low-energy resonance features. However, additional comparisons with theoretical data sets highlight wide variations. Significant resonance structures at high photon energies are explored by employing an additional series of 262 level and 896 level Dirac R-matrix calculations with a smaller six configuration target. The resulting photoionisation cross sections reproduce the main features from existing experimental observations. The results presented throughout will be useful to those requiring an extensive set of level-resolved photoionisation cross sections for astrophysical applications.
Photoionization cross-sections are obtained using the relativistic Dirac Atomic R-matrix Codes (darc) for all valence and L-shell energy ranges between 27 and 270 eV. A total of 557 levels arising ...from the dominant configurations 3s23p4, 3s3p5, 3p6, 3s23p33d, 4s, 4p, 3p53d, 3s23p23d2, 3s3p43d, 3s3p33d2 and 2s22p53s23p5 have been included in the target wavefunction representation of the Ar iii ion, including up to 4p in the orbital basis. We also performed a smaller Breit–Pauli (bp) calculation containing the lowest 124 levels. Direct comparisons are made with previous theoretical and experimental work for both valence shell and L-shell photoionization. Excellent agreement was found for transitions involving the 2Po initial state to all allowed final states for both calculations across a range of photon energies. A number of resonant states have been identified to help analyse and explain the nature of the spectra at photon energies between 250 and 270 eV.
Aims. We present rates for all E1, E2, M1, and M2 transitions among the 295 fine-structure levels of the configurations 3d9, 3d84s, 3d74s2, 3d84p, and 3d74s4p, determined through an extensive ...configuration interaction calculation. Methods. The CIV3 code developed by Hibbert and coworkers is used to determine for these levels configuration interaction wave functions with relativistic effects introduced through the Breit-Pauli approximation. Results. Two different sets of calculations have been undertaken with different 3d and 4d functions to ascertain the effect of such variation. The main body of the text includes a representative selection of data, chosen so that key points can be discussed. Some analysis to assess the accuracy of the present data has been undertaken, including comparison with earlier calculations and the more limited range of experimental determinations. The full set of transition data is given in the supplementary material as it is very extensive. Conclusions. We believe that the present transition data are the best currently available.
We have carried out a 29-state R-matrix calculation in order to calculate collision strengths and effective collision strengths for the electron impact excitation of S iii. The recently developed ...parallel RMATRX II suite of codes have been used, which perform the calculation in intermediate coupling. Collision strengths have been generated over an electron energy range of 0-12 Ryd, and effective collision strength data have been calculated from these at electron temperatures in the range 1000-100,000 K. Results are here presented for the fine-structure transitions between the ground-state configurations of 3s super(2)3p super(2) super(3)P sub(0, 1, 2), super(1)D sub(2), and super(1)S sub(0), and the values given resolve a discrepancy between two previous R-matrix calculations.
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