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Recently, Bergemann et al. reported a re-analysis of O i lines, 777 and 630 nm, using their new atomic models of O and Ni, and presented solar photospheric oxygen abundance differing from others. We discuss the accuracy of atomic data employed in their models, and demonstrate that the photoionization cross-sections (σPI) of the two levels ${\rm1s^22s^22p^33s (^5S^o_2)}$ and 1s22s22p33p(5P1), which they present as illustrations of their data in the non-local-thermodynamic-equilibrium (NLTE) model, are incorrect by large factors. For example, their σPI at the threshold of level ${\rm ^5S^o_2}$ is larger by a factor of 1000 than that of Nahar and the Opacity Project data base, TOPbase, and has an incorrect energy behaviour. They included a blending of the 630 nm line with N i for which they computed σPI in the hydrogenic approximation. The approximation does not include electron–electron interaction and hence is not valid for Ni i. They noted that the use of oscillator strengths of O i by Hibbert et al., which agree very well with TOPbase and Nahar, gave an abundance close to the existing values, but reported using averaged values of two sources. Therefore, their oxygen abundance from the new atomic models is likely to be in question.

Being the backbone element of DNA, phosphorus is a key component in the search for life in the Universe. To aid in its detection, we present line emissivity ratios for the five lowest-lying forbidden [P~II] transitions, namely those among the levels $3s^23p^2(^3P_0,^3P_1, ^3P_2,^1D_2,^1S_0)$. The wavelengths range between 0.44-70 \mum, and several lie within the spectroscopic domain observable with the James Webb Space Telescope (JWST). These line ratios have been calculated using a new collisional-radiative-recombination (CRR) model combining calculated collision strengths and level-specific recombination rate coefficients; with both datasets computed using the accurate Breit-Pauli R-Matrix method. The CRR model includes a new scheme for \eion recombination to emission line formation. We compare its effect to models incorporating only electron impact excitation and spontaneous radiative decay. We find that electron-ion recombination has a significant impact on all line ratios, and represents a major improvement in physical accuracy of emission line models., 5 pages, 4 figures

Photoionization cross sections of (Ca XV + hν → Ca XVI + e), with high energy resonant photo-absorption phenomena, of a large number of bound states, 701 in total with n ≤ 10 and l ≤ 9, are reported. They are obtained using the R-matrix method with a close coupling (CC) wavefunction expansion of 29 states of n = 2,3 complexes of the core ion Ca XVI. Characteristic features found in photoionization of the ion are illustrated with examples. The cross section (σPI) of the ground 2s22p2(3P) state is found to be unaffected by the size of the wavefunction expansion except for weak sparse resonances in high energy region. However, effects on excited states are considerable as the core excitations to n = 3 states are manifested in huge resonant absorption in high energy photoionization. They show existence of prominent high peak resonant features and enhancement in the background that were not studied before for Ca XV. In addition photoionization of the excited states with a single valence electron is dominated by Seaton resonant structures formed by the photo-excitation-of-core in the high energy region. These features will impact other quantities, such as the opacity, electron-ion recombination in high temperature plasmas where the ion exists, and hence will play important role in determination of elemental abundances in the astronomical objects.

Photoionization cross section (σPI) of P II, (hν + P II → P III + e), from ground and a large number of excited levels are presented. The study includes the resonant structures and the characteristics of the background in photoionization cross sections. The present calculations were carried out in the Breit–Pauli R-matrix (BPRM) method that includes relativistic effects. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. A singular resonance, formed by the coupling of channels in fine structure but not allowed in LS coupling, is seen at the ionization threshold of photoionization for the ground and many excited levels. The background cross section is seen enhanced compared to smooth decay for the excited levels. Examples are presented to illustrate the enhanced background cross sections at the energies of the core levels, 4P3/2 and 2D3/2, that are allowed for electric dipole transitions by the core ground level 2 P 1 / 2 o . In addition strong Seaton or photo-excitation-of-core (PEC) resonances are found in the photoionization of single valence electron excited levels. Calculations used a close coupling wave function expansion that included 18 fine structure levels of core P III from configurations 3s23p, 3s3p2, 3s23d, 3s24s, 3s24p and 3p3. Photoionization cross sections are presented for all 475 fine structure levels of P II found with n ≤ 10 and l ≤ 9. The present results will provide high precision parameters of various applications involving this less studied ion.

This report presents i) various characteristic features in photoionization cross sections (σPI) of Cl II + hν → Cl III + e for many fine structure levels of Cl II, 392 in total with n ≤ 10 and l ≤ 9, ii) comparison of features with those observed in an experiment carried out at the Advanced Light Source at Lawrence Berkeley National Lab, and iii) partial photoionization cross sections of the ground level for ionization leaving the core ion in to various excited levels for applications in plasma modeling. The features correspond to resonant structures, the shape of the background, and their interference effect in σPI of this near neutral ion Cl II with 16 electrons. σPI for the 5 levels of the ground configuration 3s23p4(3P0,1,2, 1D2, 1S0) of Cl II show regions of narrow Rydberg resonances at and near threshold energies, and resonant structures at higher energies in contrast to typical smooth decrease in the background. Various other features in σPI of levels of excited equivalent electron states and broad Seaton resonances in single valence electron excited levels are illustrated with examples. Comparison of calculated σPI of the 15 lowest levels with the combined features of the measured photoionization spectrum shows excellent agreement by reproducing and thus identifying them to the levels that they belong to. The calculations were carried out in relativistic Breit-Pauli R-matrix (BPRM) method using a close coupling wave function expansion of 45 levels up to 4s of the core ion Cl III. These levels were optimized using a set of 12 configurations going up to orbital 5s, 3s23p3, 3s3p4, 3p5, 3s23p23d, 3s23p24s, 3s23p24p, 3s23p24d, 3s23p24f, 3s23p25s, 3s3p33d, 3s23p3d2, 3p43d producing 283 levels of Cl III. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. The present results will provide high precision parameters for various applications involving this less studied ion.

Models of stellar spectra are necessary for interpreting light from individual stars, planets, integrated stellar populations, nebulae, and the interstellar medium. We provide a comprehensive and homogeneous collection of synthetic spectra for a wide range of atmospheric parameters and chemical compositions. We compile atomic and molecular data from the literature. We adopt the largest and most recent set of ATLAS9 model atmospheres, and use the radiative code ASS$\epsilon$T.The resulting collection of spectra is made publicly available at medium and high-resolution ($R\equiv\lambda/\delta\lambda$ = 10,000, 100,000 and 300,000 spectral grids, which include variations in effective temperature between 3500 K and 30,000 K, surface gravity ($0\le \log g \le 5$), and metallicity ($-5 \le$[Fe/H]$\le +0. 5$), spanning the wavelength interval 120-6500 nm. A second set of denser grids with additional dimensions, [$\alpha$/Fe] and micro-turbulence, are also provided (covering 200-2500 nm). We compare models with observations for a few representative cases., Comment: 7 pages, 4 figures. To appear in A&A

Detailed photoionization of ground and many excited states with autoionizing resonances of neutral Ti are presented. Ti I with 22 electrons forms a large number of bound states, the present work finds a total of 908 bound states with n ⩽ 10 and l ⩽ 8 . Photoionization cross sections ( σ PI ) for all these bound states have been obtained. Calculations were carried out in the close-coupling R-matrix method using a wave function expansion that included 36 states of core ion Ti II. It is found that the resonances enhance the low energy region of photoionization of the ground and low lying excited states. The resonant features will increase the opacity, as expected of astrophysical observation, and hence play important role in determination of abundances in the elements in the astronomical objects. The excited states also show prominent structures of Seaton or photo-excitation-of-core resonances.

Phosphorus abundance is crucial for DNA-based extraterrestrial life in exoplanets. Atomic data for observed spectral lines of P-ions are needed for its accurate determination. We present the first calculations for collision strengths for the forbidden PIII fine structure transition $3s^23p (^2P^o_{1/2-3/2})$ within the ground state at 17.9 $\mu$m, as well as allowed UV transitions in the $3s^23p (^2P^o_{1/2,3/2}) \rightarrow 3s3p^2 (^2D_{3/2,5/2}, ^2S_{1/2}, ^2P_{1/2,3/2})$ multiplets between 915-1345 $\AA$. Collision strengths are computed using the Breit-Pauli R-Matrix method including the first 18 levels, and they exhibit extensive auto-ionizing resonance structures. In particular, the Maxwellian averaged effective collision strength for the FIR 17.9 $\mu$m transition shows a factor 3 temperature variation broadly peaking at typical nebular temperatures. Its theoretical emissivity with solar phosphorus abundance is computed relative to H$\beta$ and found to be similar to observed intensties from planetary nebulae; the abundances derived in earlier works are 3-5 times sub-solar. The results pertain to the reported paucity of phosphorus from preferred production sites in supernovae, and abundances in planetary nebulae and supernova remnants., Comment: To appear in Mon. Not. Royal Astron. Soc. Letters, 5 pages, 3 figures

Study of characteristic features in photoionization of a large number of excited levels of Ne IV, (h ν + Ne IV → Ne V + e), using ab initio Breit–Pauli R-matrix (BPRM) method, is presented. This is the second large atomic system, after Fe XVII, for which BPRM method has been used for a full scale computation of photoionization cross sections for a large number of bound levels ( N ⩽ 10 ). The study include features, such as, of Seaton resonances due to photo-excitation-of-core and new near threshold resonant features. Coupling of fine structure channels due to relativistic effects is found to introduce low energy resonances near threshold, not allowed in LS coupling approximation. These resonances play crucial role for low temperature recombination rates. Photoionization cross sections ( σ PI ) for the largest set of levels of Ne IV, a total of 868, with n ⩽ 10 and l ⩽ 9 are presented. A wave function expansion optimized with 24 configurations with orbitals going up to 4p of core Ne V was used. Resonances due to Rydberg series of autoionizing states belonging to various core excited core levels are resolved with fine energy mesh. Details of resonant structures and enhanced background due to Seaton resonances are elaborated in this first study of the ion with relativistic effects.

Characteristic features of the resonances and background cross sections for photoionization (σPI) of oxygen-like iron ion, Fe XIX + hν → Fe XX + e, are demonstrated. The features are introduced by excitations of the core ion to states of n = 2,3,4 complexes in σPI of the ground, equivalent electron, and single valence electron excited states. Study from a large number of states is important to establish the general properties of photoionization for complex ions. This is the first detailed study of the ion with a complete set of σPI for 900 bound states with n ≤ 10 and l ≤ 9. The ion itself is of great interest for being detected in the x-ray to UV spectra of various astronomical objects. It is found that i) the ground and equivalent electron states have high peak narrow Rydberg resonances in the low energy region corresponding to n = 2 excitations only, ii) for other excited states the resonant features are stronger for core ion excitations to n = 3 complex compared to those for n = 2,4, iii) Seaton resonances due to photo-excitation of the core (PEC) are found most distinct in the energy region for dipole allowed excitation from n = 2 to n = 3 states, and iv) resonances with lower peaks in the energy region between n = 3 and n = 4 excitation indicate convergence. Computations were carried out in the R-matrix method using a large close coupling wavefunction expansion up to orbital 4f and 16 configurations. The present results should provide the data for precise modeling and applications.

Improved collisions strengths for the mid-infrared and optical transitions in Ne V are presented. Breit-Pauli R-Matrix calculations for electron impact excitation are carried out with fully resolved near-threshold resonances at very low energies. In particular, the fine structure lines at 14 micron and 24 micron due to transitions among the ground state levels 1s^22s^22p^3 (^3P_{0,1,2}), and the optical/near-UV lines at 2973, 3346 and 3426 Angstrom transitions among the ^3P_{0,1,2}, ^1D_2, ^1S_0 levels are described. Maxwellian averaged collision strengths are tabulated for all forbidden transistion within the ground configuration. Significant differences are found in the low temperature range Te < 10000 K for both the FIR and the opitcal transitions compared to previous results. An analysis of the 14/24 line ratio in low-energy-density (LED) plasma conditions reveals considerable variation; the effective rate coefficient may be dominated by the very low-energy behaviour rather than the maxwellian averaged collision strengths. Computed values suggest a possible solution to the anomalous mid-IR ratios found to be lower than theoretical limits observed from planetary nebulae and Seyfert galaxies. While such LED conditions may be present in infrared sources, they might be inconsistent with photoionization equilibrium models., 6 pages, 7 figures

Results are reported for Fe XIV energy levels and transitions obtained from the ab initio relativistic Breit–Pauli R-matrix (BPRM) method. BPRM method developed under the Iron Project is capable of calculating very large number of fine structure energy levels and corresponding transitions. However, unlike in the atomic structure calculations, where levels are identified spectroscopically based on the leading percentage contributions of configurations, BPRM is incapable of such identification of the levels and hence the transitions. The main reason for it is that the percentage contributions can not be determined exactly from the large number of channels in the R-matrix space. The present report describes an identification method that uses considerations of quantum defects of channels, contributions of channel from outer regions, Hund’s rule, and angular momenta algebra for addition and completeness of fine structure components. The present calculations are carried out using a close coupling wave function expansion that included 26 core excitations from configurations 2 s 2 2 p 6 3 s 2 , 2 s 2 2 p 6 3 s 3 p , 2 s 2 2 p 6 3 p 2 , 2 s 2 2 p 6 3 s 3 d , and 2 s 2 2 p 6 3 p 3 d . A total of 1002 fine structure levels with n ⩽ 10, l ⩽ 9, and 0.5 ⩽ J ⩽ 9.5 with even and odd parities and the corresponding 130,520 electric dipole allowed (E1) fine structure transitions, a most complete set for astrophysical modelings of spectral analysis and opacities, is presented. Large number of new energy levels are found and identified. The energies agree very well, mostly in less than 1% with the highest being 1.9%, with the 68 observed fine structure levels. While the high lying levels may have some uncertainty, an overall accuracy of energy levels should be within 10%. BPRM transitions have been benchmarked with the existing most accurate calculated transition probabilities with very good agreement for most cases. Based on the accuracy of the method and comparisons, most of the transitions can be rated with A ( ⩽ 10 % ) to C ( ⩽ 30 % ).

Far-infrared and optical [O III] lines are useful temperature–density diagnostics of nebular as well as dust obscured astrophysical sources. Fine-structure transitions among the ground state levels 1s 2 2s 2 2p 33 P0,1,2 give rise to the 52- and 88-µm lines, whereas transitions among the 3 P0,1,2, 1 D2, 1 S0 levels yield the well-known optical lines λλ4363, 4959 and 5007 A. These lines are excited primarily by electron impact excitation. However, despite their importance in nebular diagnostics collision strengths for the associated fine-structure transitions have not been computed taking full account of relativistic effects. We present Breit–Pauli R-matrix calculations for the collision strengths with highly resolved resonance structures. We find significant differences of up to 20 per cent in the Maxwellian averaged rate coefficients from previous works. We also tabulate these to lower temperatures down to 100 K to enable determination of physical conditions in cold dusty environments such photodissociation regions and ultraluminous infrared galaxies observed with the Herschel Space Observatory .W e also examine the effect of improved collision strengths on temperature- and density-sensitive line ratios.

Using the unified method, the inverse processes of photoionization and electron–ion recombination are studied in detail for neutral chromium, ( Cr I + h ν ↔ Cr II + e ), for the ground and excited states. The unified method based on close-coupling approximation and R-matrix method (i) subsumes both the radiative recombination (RR) and dielectronic recombination (DR) for the total rate and (ii) provides self-consistent sets of photoionization cross sections σ PI and recombination rates α RC . The present results show in total photoionization of the ground and excited states an enhancement in the background at the first excited threshold, 3 d 4 4 s 5 D state of the core. One prominent phot-excitation-of-core (PEC) resonance due to one dipole allowed transition ( 6 S - 6 P o ) in the core is found in the photoionization cross sections of most of the valence electron excited states. Structures in the total and partial photoionization, for ionization into various excited core states and ground state only, respectively, are demonstrated. Results are presented for the septet and quintet states with n ≤ 10 and l ≤ 9 of Cr I. These states couple to the core ground state 6 S and contribute to the recombination rates. State-specific recombination rates are also presented for these states and their features are illustrated. The total recombination rate shows two DR peaks, one at a relatively low temperature, at 630 K, and the other around 40,000 K. This can explain existence of neutral Cr in interstellar medium. Calculations were carried out in LS coupling using a close-coupling wave function expansion of 40 core states. The results illustrate the features in the radiative processes of Cr I and provide photoionization cross sections and recombination rates with good approximation for this astrophysically important ion.

New, more detailed calculations of the emission spectra of the He-like K ALPHA complex of calcium, iron and nickel have been carried out using data from both distorted-wave and R-matrix calculations. The value of the GD ratio (an extended definition of the G ratio that accounts for the effect of resolved and unresolved satellite lines) is significantly enhanced at temperatures below the temperature of He-like maximum abundance. Furthermore it is shown that satellite lines are important contributors to the GD ratio such that GD/G>1 at temperatures well above the temperature of maximum abundance. These new calculations demonstrate, with an improved treatment of the KLn (n>=3) satellite lines, that K ALPHA satellite lines need to be included in models of He like spectra even at relatively high temperatures. The excellent agreement between spectra and line ratios calculated from R-matrix and distorted-wave data also confirms the validity of models based on distorted-wave data for highly charged systems, provided the effect of resonances are taken into account as independent processes., 12 pages, 5 figures, to appear in Monthly Notices of the Royal Astronomical Society. The definitive version is available at www.blackwell-synergy.com

An extensive set of oscillator strengths ( f ), line strengths ( S ) and radiative decay rates ( A ) for the allowed and forbidden transitions in Fe XVIII is presented. The results include 1174 fine structure levels of total angular momenta J = 1/2–17/2 of even and odd parities with 2 $\le n \le$ 10, 0 $\le l \le$ 9, orbital angular momenta, 0 $\le L \le$ 11, and spin multiplicities 2, 4. These yeild about 171 500 transitions. The allowed electric dipole (E1) transitions, 141 869 in total, are obtained in the close coupling approximation using the relativistic Breit-Pauli R-matrix (BPRM) method. The forbidden electric quadrupole (E2), octupole (E3), and magnetic dipole (M1), quadrupole (M2) transitions, 29 682 in total, are obtained from configuration interaction Breit-Pauli atomic structure calculations using the code SUPERSTRUCTURE. The close coupling wavefunction expansion for Fe XVIII includes 10 levels of configurations $\rm 2s^22p^4$, $\rm 2s2p^5$, and $\rm 2p^6$ in the BRPM calculations. All fine structure levels have been identified spectroscopically. Comparison of the present energies with the available observed energies shows very good agreement. The lifetime of level $\rm 2s2p^6~^2S$ calculated from the present radiative decay rate agrees very well with the single measurement. The present decay rate for the well known E2 line arising from $\rm 2p^5(^2P^\circ_{3/2}-^2P^\circ_{1/2})$ transition within the ground state term also agrees almost exactly with NIST tabulated value. However, varying degree of agreement is found with previously calculated values for some transitions.

Radiative decay rates (A) and line strengths (S ) are presented for a large number of electric dipole allowed (E1) and forbidden electric quadrupole (E2), octupole (E3) and magnetic dipole (M1) transitions in Fe IV. The ion is amongst the most complex iron ions and exhibits effects of strong electron correlation. It has closely spaced fine structure levels from seven configurations: 3s 2 3p 6 3d 5 ,3 s 2 3p 6 3d 4 4s, 3s 2 3p 6 3d 4 4p, 3s 2 3p 6 3d 4 4d, 3s 2 3p 6 3d 3 4s4p, 3s 2 3p 6 3d 3 4s4d, 3s 2 3p 5 3d 6 before an energy gap could be noted. Atomic parameters are presented for multipole radiative transitions among the 1275 fine structure levels dominated by these seven configurations. A total of approximately 173 000 transitions of type E1, E2, E3 and M1 are presented, The set of intercombination and forbidden transitions complements the earlier extensive set of dipole allowed (∆J = 0, ±1, ∆L = 0, ±1, and ∆S = 0) fine structure transitions in Fe IV. The results are obtained in the relativistic Breit-Pauli approximation using an updated atomic structure code SUPERSTRUCTURE. Transition probabilities are compared with the existing results and varying degrees of agreement are found. The total number of transitions presented should provide a reasonably complete set for modeling of most optical to ultraviolet Fe IV spectra of astrophysical sources.

Based on new calculations we reconfirm the low and high density limits on the forbidden fine structure line ratio [O II] I(3729)/I(3726): lim_{N_ e} --> 0} = 1.5 and lim_{N_ e} --> \infty} = 0.35. Employing [O II] collision strengths calculated using the Breit-Pauli R-matrix method we rule out any significant deviation due to relativistic effects from these canonical values. The present results are in substantial agreement with older calculations by Pradhan (1976) and validate the extensive observational analysis of gaseous nebulae by Copetti and Writzel (2002) and Wang et al (2004) that reach the same conclusions. The present theoretical results and the recent observational analyses differ significantly from the calculations by MacLaughlin and Bell (1998) and Keenan et al (1999). The new maxwellian averaged effective collision strengths are presented for the 10 transitions among the first 5 levels to enable computations of [O II] line ratios., Submitted to MNRAS (Letters), 4 pages, 2 figures, 1 table

Resultsarepresentedfortheinverseprocessesof photoionizationandelectron-ionrecombinationof (h� þ Ne viii$ Ne ixþ e )a nd (h� þ Ne ix$ Ne xþ e) using the self-consistent unified method. The method employs an identical wave function expansion for both photoionization and recombination, and it includes both radiative and dielectronic recombination. Total, as well as level-specific, photoionization cross sections, � PI(E; nSLJ), and recombination rate coefficients, � R(T;nSLJ),arepresentedforallfine-structurelevelsupton� 10.Thesecorrespondtoatotalof 98bound fine-structure levels of Ne viii with 1/2� J� 17/2, and 178 bound levels of Ne ix with 0� J� 10. Total recombination cross sections and rates as functions of electron energy are also presented. The coupled channel wave function expansions for the core ions include 17 levels of Ne ix and 16 levels of Ne x. Relativistic fine structure is considered through the Breit-Pauli R-matrix (BPRM) method. The photoionization and recombination cross sections include important atomic effects such as radiation damping, channel coupling, and interference and should be of definitive

The inverse processes of photoionization and electron-ion recombination of (hnu + Ni XXVI --> Ni XXVII + e and (hnu + Ni XXVII --> Ni XXVIII + e) are studied using the unified method for the total recombination. The method subsumes both the radiative and di-electronic recombination processes and enables self-consistent sets of results for photoionization and electron-ion recombination by using the same wavefunction expansion. Photoionization cross sections (sigma_PI), recombination cross sections (sigma_{RC}), recombination collision strengths (Omega_{RC}), and recombination rate coefficients (alpha_{RC}) are obtained for ionization balance and spectral analysis of UV and X-ray lines. Level-specific photoionization cross sections and recombination rates are presented to enable accurate computation of recombination-cascade matrices for all fine structure levels n(SLJ) up to n

An extensive set of oscillator strengths (f), line strengths (S) and radiative decay rates (A) for dipole allowed, intercombination and forbidden transitions in Fe XX is presented. Results include 1792 bound fine structure levels of total angular momenta J = 1/2-19/2 of even and odd parities, with 2 ≤ n ≤ 10, 0 < l < 14, orbital angular momenta, 0 < L < 14, and total spin multiplicities 2S+1 = 2,4,6, yielding to about 3.8 x 10 5 allowed and 13,874 forbidden transitions in Fe XX. These results far exceed the available data in literature. The existing data compiled by the National Institute for Standards and Technology (NIST) are available for little over one hundred transitions, and the previously calculated data under the Opacity Project includes 75 590 LS multiplets. The present ab initio calculations are carried out in the close coupling approximation using the relativistic Breit-Pauli R-matrix method for allowed and intercombination E1 transitions. The wavefunction expansion includes 20 fine structure levels of configurations 2s 2 2p 2 , 2s2p 3 , and 2p 4 of the core ion Fe XXI. Computed energy levels are identified spectroscopically using a newly developed procedure based on quantum defects and channel contributions. All 55 observed levels have been identified and are in agreement to much less than 1% with most of the calculated values. Coefficients for radiative decays for the forbidden E2, E3, M1 transitions are obtained through atomic structure calculations including relativistic terms in the Breit-Pauli approximation using the code SUPERSTRUCTURE. The theoretical transition probabilities are compared with available values, with varying degree of agreement.

Aimed at ionization balance and spectral analysis of UV and X-ray sources, we present self-consistent sets of photoionization cross sections, recombination cross sections, and rate coefficients for photoionization of, and recombination to, Li-like O vi and He-like O vii. Relativistic fine structure is considered through the Breit-Pauli R-matrix (BPRM) method in the close-coupling approximation, implementing the unified treatment for total electron-ion recombination subsuming both radiative and dielectronic recombination processes. Self-consistency is ensured by using an identical wave function expansion for the inverse processes of photoionization and photorecombination. Radiation damping of resonances, important for H-like and He-like core ions, is included. Compared with our previous LS coupling results without radiative decay of low-n (n� 10) resonances, the presents results show significant reduction in O vi recombination rates at high temperatures. In addition to the total rates, level-specific photoionization cross sections and recombination rates are presented for all fine-structure levels n (l SLJ) up to n� 10, to enable accurate computation of recombination-cascade matrices and spectral formation of prominent UV and X-ray lines such as the 1032

In this paper, we present the first absolute measurements for photoionization of multiply charged oxygen ions: O 2+ and O 3+ in the ground state and in several metastable states, as well as relative data for O 4+ . Multiconfiguration Dirac-Fock and relativistic R-matrix calculations were performed and are tested here by comparison with experimental results. Our experimental and new theoretical results are also compared with the earlier theoretical data obtained in the R-matrix approximation to calculate photoionization cross sections over part of the isonuclear series of multiply charged oxygen ions. Subject headings: atomic data — methods: laboratory

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, Submitted to Astron. Astrophys., 13 pages : Radiative data for Ne-like Iron for X-ray and EUV applications

Absolute photoionization cross sections have been measured for a mixture of ground-state and metastable O ii (O + ) ions at photon energies ranging from 29.9 to 46.0 eV (414.7 to 269.5 A ˚ ). All measurements were performed by merging an O + beam with synchrotron radiation from an undulator beam line at the Advanced Light Source (ALS). At a resolution of 17 meV, more than 70 spectral features have been resolved, most of them identified and characterized. These measurements are compared with two independent R-matrix calculations and the data in TOPbase. All three calculations agree within 25% on the direct photoionization cross section, and with the absolute measurements within 40%. Some differences are noted in the predicted resonance positions among the three close-coupling R-matrix calculations, the TOPbase data being the least accurate. The estimated total experimental uncertainty varies from 15% to 20%. Such measurements benchmark theoretical photoionization cross section calculations performed within the framework of the Opacity Project and the Iron Project. Subject headings: atomic data — atomic processes — methods: laboratory

Photoionization and recombination cross sections and rate coefficients are calculated for Li-like Fe XXIV and He-like Fe XXV using the Breit-Pauli R-matrix (BPRM) method. A complete set of total and level-specific parameters is obtained to enable X-ray photoionization and spectral modeling. The ab initio calculations for the unified (e + ion) recombination rate coefficients include both the non-resonant and the resonant recombination (radiative and di-electronic recombination, RR and DR, respectively) for (e + Fe XXV) -> Fe XXIV and (e + Fe XXVI) -> Fe XXV. The level specific rates are computed for all fine structure levels up to n = 10, enabling accurate computation of recombination-cascade matrices and effective rates for the X-ray lines. The total recombination rate coefficients for both Fe XXIV and Fe XXV differ considerably, by several factors, from the sum of RR and DR rates currently used to compute ionization fractions in astrophysical models. As the photoionization/recombination calculations are carried out using an identical eigenfunction expansion, the cross sections for both processes are theoretically self-consistent; the overall uncertainty is estimated to be about 10-20%. All data for Fe XXIV and Fe XXV (and also for H-like Fe XXVI, included for completeness) are available electronically.

The first complete set of unified cross sections and rate coefficients are calculated for photoionization and recombination of He- and Li-like ions using the relativistic Breit-Pauli R-matrix method. We present total, unified (e + ion) recombination rate coefficients for (e + C VI ---> C V) and (e + C V \longrightarrow C IV) including fine structure. Level-specific recombination rate coefficients up to the n = 10 levels are also obtained for the first time; these differ considerably from the approximate rates currently available. Applications to recombination-cascade coefficients in X-ray spectral models of K-alpha emission from the important He-like ions is pointed out. The overall uncertainty in the total recombination rates should not exceed 10-20%. Ionization fractions for Carbon are recomputed in the coronal approximation using the new rates. The present (e + ion) recombination rate coefficients are compared with several sets of available data, including previous LS coupling results, and `experimentally derived' rate coefficients. The role of relativistic fine structure, resolution of resonances, radiation damping, and interference effects is discussed. Two general features of recombination rates are noted: (i) the non-resonant (radiative recombination) peak as E,T ---> 0, and the (ii) the high-T resonant (di-electronic recombination) peak.

Photoionization cross sections, σPI, and electron-ion recombination rate coefficients, αR, for silicon-like ions are calculated. Calculations are carried out in the close coupling approximation using the R-matrix method. Each ion has a large number of bound states with n ≤ 10 and l ≤ 9: 433 for Ar V, 631 for Ca VII, and 1223 for Fe XIII. Both the partial photoionization cross sections leaving the core ion in the ground state and the total cross sections for ionization in the ground state as well as the excited core states are obtained for all bound states. The electron-ion recombination rates are obtained using a unified method, based on the close coupling R-matrix method, that incorporates both the radiative and dielectronic recombination processes in a self-consistent and unified manner. Total recombination rate coefficients are presented for a wide range of temperatures for practical applications. State-specific recombination rate coefficients for individual bound states are also presented. Results of Si I and S III, derived from earlier works, are also presented for completeness.

Ionization balance in the low-ionization stages of iron is important in a variety of astrophysical plasmas. Accurate recombination rates are needed but are difficult to compute in a detailed quantum mechanical treatment. The main difficulty lies in the complexity of strong electron-electron correlation arising due to the open 3d shell. We present the total electron-ion recombination rate coefficients for the process, e+Fe VI → Fe V, obtained in an ab initio manner. Large-scale computations are carried out in the close coupling (CC) approximation using the R-matrix method employing a unified treatment that considers the infinite number of states of the recombined ion and incorporates both the radiative recombiantion (RR) and the dielectronic recombination (DR) processes in a self-consistent manner. It involves calculations of detailed photoionization cross sections, σPI, with autoionizing resonances of a large number of bound states with n≤nmax, such as 1054 bound states for the present case of Fe V. The number also equals the total number of state-specific recombination rates obtained for the ion. The high-n states are treated through the DR theory by Bell & Seaton. The same wavefunction expansion is employed in all photoionization/recombination calculations, thereby ensuring self-consistency. Rates are presented at a wide range of temperature for all practical applications. Present rates for total recombination differ considerably from currently used values obtained using simpler approximations. Application of the new recombination rate coefficients and photoionization cross sections for the ionization structure of iron in planetary nebulae show that under typical conditions the relative fractions of Fe V and Fe VI change by nearly a factor of 2.

We present a comprehensive and self-consistent set of new atomic data for ionization balance in radi- atively and collisionally ionized astrophysical plasmas. Complex resonant phenomena resulting in rapid energy variation in the cross sections for photoionization and recombination require accurate and large- scale calculations, as reported. Another new development is the consideration of the uni-ed nature of the recombination process in an ab initio manner, via resonances embedded in the electron-ion continua, which have been heretofore considered as separate processes of radiative recombination and dielectronic recombination. A single set of total electron-ion recombination rate coefficients is thereby obtained as a function of electron temperature. The present calculations also meet the hitherto neglected, but theoreti- cally essential, criterion of self-consistency between the rates for the inverse processes of photoionization and recombination, ensured by describing all atomic processes with an identical set of eigenfunction expansion within the close-coupling approximation using the R-matrix method. Photoionization cross sections and total electron-ion recombination rate coefficients for the carbon and nitrogen isonuclear sequences, C IEC VI and N IEN VII, are presented. Ionization fractions in coronal equilibrium are also computed. The present photoionization cross sections have been calculated using more extensive eigen- function expansions than those in the Opacity Project. In addition to the total photoionization and recombination data, state-speci-c cross sections are also obtained for a large number of excited states for non-LTE models. Complete data sets are available electronically. Subject headings: atomic data E atomic processes E plasmas

The total and state-specific electron-ion recombination rate coefficients are obtained for Fe I. The calculations are carried out using a new ab initio method that incorporates both the radiative and the dielectronic recombination processes in an unified and self-consistent manner. The computations employ the close coupling approximation and the R-matrix method from atomic collision theory. A 52 state close coupling eigenfunction expansion dominated by the states of the ground 3d64s and excited 3d7, 3d64p, 3d54s2, and 3d54s4p configurations of Fe II are used in the present calculations. The important electron correlation and radiation damping effects are included via explicit coupling of autoionization and radiative channels. This is the first detailed atomic calculation for the recombination rates for Fe I. The present rates are considerably higher than the radiative recombination rates being used currently in the low-temperature region, T ≤ 104 K, whereas they are about 4 times lower than those given by the Burgess general formula for dielectronic recombination at higher temperatures. The implications of the new recombination rate coefficients and photoionization cross sections for Fe I on the ionization structure of iron in the cold neutral interstellar medium are studied. It is found that the ratio of Fe II to Fe I obtained with the new atomic data increases by a factor of about 3-30 over previous calculations.

It is shown that above the temperature of maximum abundance, recombination rates into the excited states of He-like ions that are calculated using earlier, more approximate methods differ markedly from rates obtained from recent distorted-wave and R-Matrix calculations (unified recombination rate coefficients) for Ca, Fe, and Ni. The present rates lead to G ratios that are greatly lower than those resulting from the more approximate rates in previous works, by up to a factor of six at high electron temperatures. Excellent agreement between the distorted-wave and the R-Matrix rates, as well as excellent agreement in the G ratios calculated from them, provides support for the accuracy of these new values which have a broad applicability to the modelling and interpreting of X-ray spectra from a variety of astrophysical and laboratory sources., Comment: 11 pages including LANL cover, 6 figures. Minor typos corrected to conform to the version that will appear in print in MNRAS. The definitive version is available at http://www.blackwellsynergy.com. Specifically http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2966.2007.12410.x

We present new calculations for transition probabilities of Fe IV, with much more extensive datasets than heretofore available. The large-scale close coupling R-matrix calculations yield 1,798 LS bound states with n $\leq$ 11 and $l \leq$ 9, and corresponding transition probabilities for 138,121 dipole allowed transitions in the form of oscillator strengths $f$, line strengths $S$, and A-coeffficients for a variety of applications. This represents the largest R-matrix dataset in LS coupling for any ion under either the Opacity Project or the Iron Project. Through algebraic transformation of the LS multiplets, a total of 712,120 dipole allowed fine structure transitions for Fe IV are obtained. Observed transition energies are used together with the energy independent line strengths to derive the $f$- and the $A$-values; the adopted algorithm used calculated energies for the remainder. Present results show significantly better accuracy for the important low-lying states than previous calculations. Monochromatic and mean opacities for Fe IV are computed and compared with those obtained using the Opacity Project data. We find differences which could have important consequences for several astrophysical applications involving low ionization stages of iron., 10 pages, 1 figire, submitted to Astronomy and Astrophysics

We present theoretical iron emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The non-local thermodynamic equilibrium (NLTE) models include a new and extensive treatment of radiative transfer in the FeIII ion, complementing the FeII emission line strengths predicted in our earlier works. We also briefly present preliminary results for the FeI emission from AGN using a reduced atom model. We can satisfactorily reproduce the empirical UV FeIII emission line template of Vestergaard & Wilkes (2001) for the prototypical narrow-line Seyfert 1 galaxy I Zw 1, both in terms of the general FeIII flux distribution and the relative strength of the FeIII and FeII emission. However, a number of detailed features are still not matched; the most prominent example is the strongest single FeIII feature observed in the I Zw 1 spectrum, UV47: it is predicted to be strong only in models suppressing Fe-H charge exchange reactions. We examine the role of variations in cloud turbulent velocity and iron abundance and carry out Monte Carlo simulations to demonstrate the effect of uncertainties in atomic data on the computed spectra., 30 pages, 11 eps figures Submitted to ApJ

Ar XIII is found to be unique with new features in electron-ion recombination not seen in any other ion. The ion has been studied with the unified method which provides a theoretically self-consistent set of atomic parameters for the inverse processes of photoionization and total electron-ion recombination. The unified method subsumes both the radiative recombination (RR) and dielectronic recombination (DR) within the framework of close-coupling formulations using the R-matrix method. A set of four DR "bumps", two in the low and two in the high temperature regions, is found to exist in the recombination rates of Ar XIV + e $\to$ Ar XIII. This is in contrast to two typical DR "bumps", one at high temperature common for most ions and one at low temperature depending on the presence of near threshold autoionizing resonances in the bound-free process. The large scale ab initio calculations for Ar XIII employ eigenfunction expansion of 37 core Ar XIV states from n = 2 and 3 complexes. This enables core excitations of type $\Delta n$ = 0 and 1. Ar XIII exhibits more extensive resonant structures and wider PEC (photoexitation-of-core) resonances for n = 3 core states than those of n = 2 states. Hence the high energy region of photoionization and recombination are dominated by these structures. Total and partial photoionization cross sections of all bound states, state-specific recombinaion rates of 561 bound states and total recombination rate coefficients are presented., Comment: 28 pages, 7 figures, ApJS (in press)

The K-alpha resonance complexes in oxygen ions O I - O VI are theoretically computed and resonance oscillator strengths and wavelengths are presented. The highly resolved photoionization cross sections, with relativistic fine structure, are computed in the coupled channel approximation using the Breit-Pauli R-matrix method. A number of strong K-alpha resonances are found to be appreciable, with resonance oscillator strengths f_r > 0.1. The K-alpha resonance wavelengths of O I-O VI lie in a relatively narrow wavelength range 22 - 23.5 A, and the X-ray opacity in this region should therefore be significantly affected by K --> L transitions in oxygen. The results should be useful in the interpretation of soft X-ray spectra observed from Chandra and XMM-Newton., Monthly Notices of Roy. Astro. Soc. (in press), 10 pgs. 1 figure

Ab initio calculations including relativistic effects employing the Breit-Pauli R-matrix (BPRM) method are reported for fine structure energy levels and oscillator strengths upto n = 10 and 0.leq. l .leq.9 for 15 Li-like ions: C IV, N V, O VI, F VII, Ne VIII, Na IX, Mg X, Al XI, Si XII, S XIV, Ar XVI, Ca XIII, Ti XX, Cr XXII, and Ni XXVI. About one hundred bound fine structure energy levels of total angular momenta, 1/2 .leq. J .leq. 17/2 of even and odd parities, total orbital angular momentum, 0 .leq L .leq. 9 and spin multiplicity (2S+1) = 2, 4 are considered for each ion. The levels provide almost 900 dipole allowed and intercombination bound-bound transitions. The BPRM method enables consideration of large set of transitions with uniform accuracy compared to the best available theoretical methods. The CC eigenfunction expansion for each ion includes the lowest 17 fine structure energy levels of the core configurations 1s^2, 1s2s, 1s2p, 1s3s, 1s3p, and 1s3d. The calculated energies of the ions agree with the measured values to within 1% for most levels. The transition probabilities show good agreement with the best available calculated values. The results provide the largest sets of energy levels and transition rates for the ions and are expected to be useful in the analysis of X-ray and EUV spectra from astrophysical sources., 16 pgs., to appear in Astronomy and Astrophysics

We present the first detailed ab initio quantum mechanical calculations for total and state-specific recombination rate coefficients for e + Ni III --> Ni II. These rates are obtained using a unified treatment for total electron-ion recombination that treats the nonresonant radiative recombination and the resonant dielectronic recombination in a self-consistent unified manner in the close coupling approximation. Large-scale calculations are carried out using a 49-state wavefunction expansion from core configurations 3d^8, 3d^74s, and 3d^64p that permits the inclusion of prominent dipole allowed core transitions. These extensive calculations for the recombination rates of Ni II required hundreds of CPU hours on the Cray T90. The total recombination rate coefficients are provided for a wide range of temperature. The state-specific recombination rates for 532 bound states of doublet and quartet symmetries, and the corresponding photoionization cross sections for leaving the core in the ground state, are presented. Present total recombination rate coefficients differ considerably from the currently used data in astrophysical models., ApJ Suppl. (submitted), 4 figures

Photoionization cross sections and electron-ion recombination rate coefficients are presented for carbon-like ions obtained using methods developed for the Opacity Project. General features of the new data are dis­ cussed, and their astrophysical relevance is pointed out. The illustrative results for photoionization include extensive autoionization resonance structures and partial photoionization into specific states of the residual ion. It is shown that the excited state photoionization cross sections are not, in general, described by hydro­ genic behavior and often contain strong resonances due to photoexcitation corresponding to dipole transitions in the core ion; these are referred to as photoexcitation-of-core resonances that attenuate the background cross section over much larger energy ranges than the Rydberg type of resonances. The effective photoioniza­ tion cross sections are thus considerably enhanced, for excited bound states, relative to the hydrogenic form. A new method is described for the calculation of total recombination rate coefficients that accounts for both the radiative and the dielectronic recombination processes in an ab initio manner. The recombination calculations are carried out in the close coupling approximation using the Milne relation with detailed photoionization cross sections for large numbers of excited states of each atom or ion, and employing a precise theory of dielectronic recombination given by Bell & Seaton. The present recombination rate coefficients are compared with earlier works on radiative and dielectronic recombinations treated separately and significant differences are noted. Recombination rate coefficients are presented for C I, N n, 0 III, F IV, and Ne v at a wide range of temperatures for astrophysical applications. Subject headings: atomic data - atomic processes