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Atomic structure calculations involving optimization of radial integrals - Energy levels and oscillator strengths for Fe XII and Fe XIII 3p-3d and 3s-3p transitions
... There are 36 measured bound levels, corresponding to 24 LS terms, below the ionization threshold [1]. Among the previous theoretical studies are multi-configuration Dirac-Fock calculations by Huang [2], Hartree-Fock calculations by Fawcett et al. [3], Hartree-Fock calculations including relativistic effects by Bromage et al. [4] and by Fawcett [5], and multi-configuration Thomas-Fermi calculations by Kastner et al. [6]. The lifetime of one single level, 3s3p 3 3 S 1 o , has been measured by Träbert et al. [7]. ...
... The disagreement with [2] shown for the 3s 2 3p 2 ( 3 P) → 3s3p 3 ( 3 S o ) transition may be spurious; rather good agreement is actually seen if the 3s3p 3 ( 3 S o ) and 3s3p 3 ( 1 P o ) state labels are switched in [2]. Varying degrees of agreement with the oscillator strengths are found by Fawcett and collaborators (Fawcett et al. [3], Bromage et al. [4], and Fawcett [5]). While present values agree very well with those given by Fawcett et al. [3] for transitions such as 3s 2 3p 2 ( 1 D) → 3p4s( 1 P o ), 3p3d( 3 F o ) → 3p4p( 3 D), the agreement is quite poor for some other transitions such as for 3s 2 3p 2 ( 3 P) → 3p4s( 3 P o ). ...
... The f-values from the three calculations, Refs. [13], and [4] and the present, agree in general for the LS transition (Table C), indicating similar predictions for the lifetime (Table D). However, the slight variation in the calculated energies will introduce some differences. ...
Oscillator strengths, line strengths, and transition probabilities for fine-structure levels in silicon-like iron, Fe XIII, are reported. The data obtained are for 1223 LS bound terms, 64,456 LS multiplets, and 307,863 fine-structure transitions. Calculations are carried out in LS coupling using the close coupling R-matrix approximation with a 14-term eigenfunction expansion. The fine-structure components are obtained through algebraic transformations. Present data considerably exceed the observed and the previously calculated data available, including those from the Opacity Project. Comparisons with previously measured and calculated values are made.
... Even the strongest lines in Fe XIII, which fall into the EUV wavelength range of the Hinode/EIS, have dubious identifications. Most of the Fe XIII lines involving the 3s 2 3p 2 , 3s3p 3 , and 3s 2 3p3d configurations in the EUV were identified by Fawcett's group (Fawcett 1970(Fawcett , 1971Behring et al. 1976;Bromage et al. 1978). Del Zanna (2011) reviewed these identifications and proposed several new lines, using atomic data from Storey & Zeippen (2010). ...
... The reason behind this issue is that the line 202.424 Å from Behring et al. (1976) was incorrectly assigned to the transition #2/3s 2 3p 2 3 P 1 -#22/3s 2 3p 3d 3 P 0°o f Fe XIII (Bromage et al. 1978). ...
The multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction methods are used to provide excitation energies, lifetimes, and radiative transition data for the 604 (699, 702, 704, 704, 704, and 699) lowest levels of the 3 s ² 3 p ² , 3 s 3 p ³ , 3 s ² 3 p 3 d , 3 p ⁴ , 3 s 3 p ² 3 d , 3 s ² 3 d ² , 3 p ³ 3 d , 3 s 3 p 3 d ² , 3 s 3 d ³ , 3 p 3 d ³ , 3 p ² 3 d ² , 3 s ² 3 p 4 s , 3 s ² 3 p 4 p , 3 s ² 3 p 4 d , 3 s ² 3 p 4 f , 3 s 3 p ² 4 s , 3 s 3 p ² 4 p , 3 s 3 p ² 4 d , 3 s 3 p ² 4 f , 3 s ² 3 d 4 s , 3 s ² 3 d 4 p , 3 p ³ 4 s , 3 p ³ 4 p , 3 s 3 p 3 d 4 s , 3 s ² 3 p 5 s , and 3 s ² 3 p 5 p configurations in Cr xi , (Mn xii , Fe xiii , Co xiv , Ni xv , Cu xvi , and Zn xvii ). Previous line identifications of Fe xiii and Ni xv in the EUV and X-ray wavelength ranges are reviewed by comprehensively comparing the MCDHF theoretical results with available experimental data. Many recent identifications of Fe xiii and Ni xv lines are confirmed, and several new identifications for these two ions are proposed. A consistent atomic data set with spectroscopic accuracy is provided for the lowest hundreds of levels for Si-like ions of iron-group elements of astrophysical interest, for which experimental values are scarce. The uncertainty estimation method suggested by Kramida, applied to the comparison of the length and velocity line strength values, is used for ranking the transition data. The correlation of the latter with the gauge dependency patterns of the line strengths is investigated.
... In this sequence the spectra from Si I to K VI are known [1]. From Ca VII to Cu XVI the analysis of the spectra is incomplete [2][3][4][5][6][7][8][9][10][11][12][13]. For higher ionization states in this sequence, Tra¨bert et al. [14] reported the intercombination lines 3s 2 3p 2 3 P 2 23s3p 3 5 S 2 and 3s 2 3p 2 3 P 1 23s3p 3 5 S 2 : Sugar et al. [15] have reported on spectra generated in tokamak plasma from Cu XVI to Mo XXIX and from Cu XVI to As XX from laser-produced plasmas. ...
Wavelengths from radiation of plasmas produced by a Nd:YAG/glass laser focused on targets of V, Cr, Mn, Fe, Co, Ni and Cu, have been recorded photographically in the region of 270–600 Å with a 3 m normal incidence spectrograph. For this sequence (V X–Cu XVI) we have identified 16 new lines which belong to the 3s23p23s23p2–3s3p33s3p3 transition array. From these transition we have determined 11 new levels of the 3s3p33s3p3 configuration. Hartree–Fock calculations with relativistic corrections were used to predict energy levels and transitions. Isoelectronic extrapolations along the Si I sequence are used to support the experimental results.
The Data Center on Atomic Transition Probabilities at the National Bureau of Standards, Washington, D.C., has continued its bibliographical and critical compilation work on transition probabilities. A new general bibliography has been published, covering the literature references through October 1977 (1).
X-ray and ultraviolet (UV) observations of the outer solar atmosphere have been used for many decades to measure the fundamental parameters of the solar plasma. This review focuses on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths, and discusses some of the diagnostic methods that have been used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances. We mainly focus on methods and results obtained from high-resolution spectroscopy, rather than broad-band imaging. However, we note that the best results are often obtained by combining imaging and spectroscopic observations. We also mainly focus the review on measurements of electron densities and temperatures obtained from single ion diagnostics, to avoid issues related to the ionisation state of the plasma. We start the review with a short historical introduction on the main XUV high-resolution spectrometers, then review the basics of optically thin emission and the main processes that affect the formation of a spectral line. We mainly discuss plasma in equilibrium, but briefly mention non-equilibrium ionisation and non-thermal electron distributions. We also summarise the status of atomic data, which are an essential part of the diagnostic process. We then review the methods used to measure electron densities, electron temperatures, the DEM, and relative chemical abundances, and the results obtained for the lower solar atmosphere (within a fraction of the solar radii), for coronal holes, the quiet Sun, active regions and flares.
The fully relativistic multiconfiguration Dirac--Hartree--Fock method is used to compute excitation energies and lifetimes for the 143 lowest states of the $3s^23p^3$, $3s3p^4$, $3s^23p^23d$, $3s3p^33d$, $3p^5$, $3s^23p3d^2$ configurations in P-like ions from Cr X to Zn XVI. Multipole (E1, M1, E2, M2) transition rates, line strengths, oscillator strengths, and branching fractions among these states are also given. Valence-valence and core-valence electron correlation effects are systematically accounted for using large basis function expansions. Computed excitation energies are compared with the NIST ASD and CHIANTI compiled values and previous calculations. The mean average absolute difference, removing obvious outliers, between computed and observed energies for the 41 lowest identified levels in Fe XII is only 0.057 \%, implying that the computed energies are accurate enough to aid identification of new emission lines from the sun and other astrophysical sources. The amount of energy and transition data of high accuracy is significantly increased for several P-like ions of astrophysics interest, where experimental data are still very scarce.
The title of our Commission was last changed in 1964 from “Commission des Etalons de Longueur d’Onde et des Tables de Spectres” to the present title recognizing the broader scope of the Commission. This was initiated by new observing techniques and refined theoretical models. In 1966 it was decided to add two more objects to the work of the Commission: Broadening of spectral lines and collision cross sections. The present structure of the Commission dates back to 1970. Since then the work of the Commission is not well described by the name “Fundamental Spectroscopic Data”. This is a hindrance in the recruitment of new members, especially those who represent new fields of interest. But the answers to an enquiry about change of name were so divergent within our Commission that so far no action was taken.
Following a summary of early solar EUV spectroscopy the spectra of some late-type stars obtained with the Extreme Ultraviolet Explorer ( EUVE ) are briefly surveyed. Some transitions which are not included in current emissivity codes but could lead to numerous weak lines, and an apparent continuum in the EUVE short wavelength region, are discussed. The importance of the geometry adopted when interpreting the emission measure distribution is stressed, since radial factors can lead to an apparent emission measure distribution gradient that is steeper than the value of 3/2 expected in plane parallel geometry.
The Arcetri-95 spectral code for optically thin plasmas computes the continuum and line emission of the ions of the most abundant elements. It includes the most updated atomic models and the main atomic processes for ions from Fe IX to Fe XXIII and for ions of the Belike, C-like, and N-like isoelectronic sequences. The power emitted per unit emission measure is produced as a function of temperature and density.
Comparison with observations requires the knowledge of the differential emission measure (DEM) as a function of temperature. A numerical code evaluates the best DEM distribution that satisfies observations and theoretical predictions. The spectral code together with the DEM code allows to compute synthetic spectra for any specified temperature distribution model of the plasma.
It is important to investigate whether non—relativistic errors in calculated oscillator strengths and related atomic data are large enough to obscure corrections applied in relativistic calculations. The magnitude such errors is however difficult to estimate. This is just one reason why the accuracy of the atomic data needs careful scrutiny. Application to the analysis of line intensities in laboratory and astropyhsical plasmas is a more general one. This review therefore focuses on errors that can affect the accuracy of calculated oscillator strengths. Precautions that can be taken to minimise errors arising from different causes are surveyed. Special attention is given to their reduction through the improvement of eigenvectors with Slater parameter optimisation methods. These semi-empirical methods for improving the accuracy of oscillator strengths can be important in fully relativistic calculations for a range of ions.
Energy levels, radiative rates, oscillator strengths and line strengths are reported for transitions among the lowest 97 levels of the (1s22s22p6) 3s23p2, 3s23p3d, 3s3p3, 3p4, 3s3p23d, and 3s23d2 configurations of Rb XXIV. A multiconfiguration Dirac–Fock (MCDF) method is adopted for the calculations. Radiative rates, oscillator strengths, and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions from the ground level to all 97 levels, although calculations are performed for a much larger number of levels. To achieve the accuracy of the data, comparisons are provided with similar data obtained from the Flexible Atomic Code (FAC) and also with the available theoretical and experimental results. Our energy levels are found to be accurate to better than 1.2%. Wavelengths calculated are found to lie in EUV (extreme ultraviolet) and x-ray regions. Additionally, lifetimes for all 97 levels are obtained for the first time.
We present high-resolution laboratory measurements of the emission from various ions of C, N, O, F, Ne, S, Ar, Fe, and Ni in the extreme ultraviolet wavelength band centered around the λ211 Fe XIV channel of the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. While all of the strong iron lines in this region are well known, we note many weaker lines of iron that are not yet identified. The high resolution of our measurements also allows us to resolve several lines in Fe XI, Fe XII, and Fe XIII between 200 and 205 Å, whose identities were in question based on a disagreement between different databases. The spectra of the elements other than iron are much less known, and we find a multitude of lines that are not yet in the databases. For example, the CHIANTI database clearly disagrees with the NIST data listings on several of the argon lines we observe and also it contains only about half of the observed sulfur lines.
In the framework of the IRON Project we have performed new, fully
quantum mechanical atomic calculations for the Fexii (Fe(11+) ) coronal
ion. Energy levels, oscillator strengths and spontaneous decay
transition probabilities have been computed by including extensive
configuration interaction (CI) and relativistic effects in the solution
of the atomic structure problem. The R-matrix approach has been employed
to solve the electron scattering problem and generate a new set of
collisional atomic data. Results are discussed for the ten
fine-structure forbidden transitions in the 3s(23p^3) ground
configuration of Fexii, and compared with previous calculations.
A practical approach to calculating diagnostic parameters includes both
scattering and statelike (autoionization) elements. The paper presents
inelastic quasi-projection-operator calculations of autoionization
states of the three-electron ions of oxygen and silicon for states below
the n = 3 manifod of the respective two-electron parent (O VI and Si
XII). Wave functions containing up to 40 configurations are calculated.
The O VI calculated results agree with experimental results within the
experimental error (about + or - 2 eV) while for the Si XII case, it was
necessary to include relativistic effects. Where formulas are available
(states for which p + q = 2), the Si XII results are also in good
agreement with experimental results for 2Se, 2Po, and 2De states. Since
the calculated results for some of the higher states did not agree with
identifications proposed by Trabert et al. (1979), alternative
identifications are suggested.
Excitation energies and radiative rates for electric dipole (E1) transitions among the 86 fine-structure levels belonging to the configurations (1s
22s
22p
6)3s
23p
2, 3s3p
3, 3s
23p3d, 3p
4, 3s
23p4s, 3s
23p4p, 3s3p
2(2S)4s, 3s3p
2(2P)4s, 3s3p
2(4P)4s, 3s3p
2(2D)4s, 3s
23p4d and 3s
23p4f of Cl IV are calculated using extensive configuration-interaction (CI) wave functions obtained with the CIV3 computer code of Hibbert. The relativistic effects in intermediate coupling are incorporated by means of the Breit-Pauli Hamiltonian. In order to keep the calculated energy splittings close to the energy values of the National Institute for Standards and Technology, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. Our calculated energy levels, including their orderings, are in excellent agreement with the available NIST values. The mixing among several fine-structure levels is found to be very strong. From our radiative rates we have also calculated radiative lifetimes of the fine-structure levels. Significant differences between our calculated lifetimes and those from a sophisticated calculation for a few low lying levels are noted and discussed. In this calculation, we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.
Theoretical wavelengths and weighted oscillator strengths are tabulated for spectral emission lines of the ions Cl V, Ar VI, Ca VIII, Ti X, Cr XII, Fe XIV, and Ni XVI, together with available measured wavelengths. The computations are made in a theoretical framework which includes all configuration-interactions within the complex of principal quantum number n = 3 and involves the scaling of ab initio values of Slater radial energy integrals based on empirical data. The empirical scale factors and the adopted Slater parameters are listed along with derived energy levels and wave functions. Racah reduced radial dipole matrix elements are also given.
Laboratory measurements of the n = 3 to n = 3 emission from M-shell iron ions are presented and compared to synthetic spectra from the CHIANTI spectral model. The measurements cover the range 170-290 Angstrom-Sign and are made at an electron density of about 10{sup 11} cm{sup -3}. Emission from Fe VIII through Fe XVI has been identified. Excellent agreement with CHIANTI predictions is found for most lines. Twenty weaker features are noted in the laboratory data that are either absent in CHIANTI or have recently been added and correspond to lines that have not been verified by experimental measurements. A few of these lines may have already been observed (but not yet identified) in the Sun. The features are attributed to emission from various charge states of iron, notably Fe IX and Fe XIII, and two features have been identified as transitions in Fe VIII, i.e., the 3p{sup 6}3d {sup 2}D{sub 5/2}-3p {sup 5}3d{sup 2} {sup 2}P{sub 3/2} and the 3p {sup 6}3d {sup 2}D{sub 3/2}-3p {sup 5}3d{sup 2} {sup 2}P{sub 1/2} transitions at 225.25 {+-} 0.12 and 226.35 {+-} 0.10 Angstrom-Sign , respectively. Seven lines in Fe XI, Fe XII, and Fe XIII between 200 and 205 Angstrom-Sign are noted for which the wavelengths in the CHIANTI database disagree with those in the current database of the National Institute of Standards and Technology. Our measurements of five of these lines appear to agree with the assignments used in CHIANTI.
We have performed large-scale CIV3 calculations of excitation energies from ground state for 69 fine-structure levels as well as of oscillator strengths and radiative decay rates for all electric-dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to the (1s22s22p6)3s23p2, 3s3p3, 3p4, 3s23p3d, 3s23p4s, 3s23p4p, 3s23p4d, and 3s23p4f configurations of Cu XVI. These states are represented by very extensive configuration-interaction (CI) wave functions obtained with the computer code CIV3 of Hibbert. The important relativistic effects in intermediate coupling are incorporated by means of the Breit-Pauli Hamiltonian. Small adjustments to the diagonal elements of the Hamiltonian matrices have been made so that the energy splittings are as close as possible to the energy values of those from the National Institute for Standards and Technology. The mixing among several fine-structure levels is found to be very strong. From our radiative decay rates we have also calculated radiative lifetimes of the fine-structure levels. Our calculated lifetime for the high spin level 3s3p3(5S2) is found to be in excellent agreement with the experimental value of Trabert et al (1988 J. Opt. Soc. Am. B 5 2173). In this calculation, we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available. ).
Energy levels and radiative rates for transitions among the lowest 97 fine-structure levels belonging to the (1s22s22p6) 3s23p2, 3s3p3, 3s23p3d, 3p4, 3s3p23d and 3s23d2 configurations of Fe XIII have been calculated using the fully relativistic GRASP code. Additionally, collision strengths for transitions among these levels have been computed using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (\cite{Norrington04}). Radiative rates and oscillator strengths are tabulated for all allowed transitions among the 97 fine-structure levels, while collision strengths are reported for some transitions at a few energies above thresholds. Comparisons are made with the available results, and the accuracy of the data is assessed. Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/371
These tables contain calculated wavelengths and oscillator strengths as well as measured wave-lengths for 3s23p2-3s3p3 and 3s23p2-3s23p3d transitions, and energy levels and level compositions for the 3s3p3 and 3s23p3d configurations, of ions in the Si I isoelectronic sequence between Si I and Ni XV. The computational method is the same as that recently applied to analogous transition arrays in S-like and P-like ions, which involved the optimization of Slater parameters previously calculated ab initio with a Hartree-Fock-Relativistic (HFR) program package which includes configuration interaction. This package employs the Blume-Watson method for spin-orbit interactions.A Multiconfiguration-Dirac-Fock program is applied to check the accuracy of ab Initio HFR calculations for Fe XIII. Statistics are also tabulated to demonstrate how optimization procedures and the inclusion of strongly interacting configurations affect the values of the oscillator strengths.
Non-orthogonal orbitals in the multiconfiguration Hartree–Fock approach are used to calculate line strengths, oscillator strengths and transition probabilities for E1 transitions among the fine-structure levels of the 3s23p3, 3s3p4, 3s23p23d, 3s3p33d, 3p5 and 3s23p3d2 configurations in Fe XII and 3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2, 3p3d2, 3s24s, 3s24p, 3s3p4s and 3s24d configurations in Fe XIV. The lifetimes of excited levels belonging to these configurations of Fe XII and Fe XIV are also presented. An accurate representation of the levels has been obtained using spectroscopic and correlation radial functions. The wavefunctions exhibit large correlations and significant dependence of one-electron valence orbitals due to both the total and intermediate terms. The relativistic corrections are included through the one-body and two-body operators in the Breit–Pauli Hamiltonian. Progressively larger calculations are performed to check for important electron correlation contributions and for convergence of results. The atomic wavefunctions give excitation energies which are in close agreement with experiment. The present oscillator strengths and transition probabilities compare very well with previous large scale calculations.
The effective collision strengths for fine-structure transitions within the ground 3s23p2 configuration and from the ground 3s23p2 configuration to the excited 3s3p3 configuration in Fe XIII are calculated using R-matrix approach in an intermediate-coupling scheme. The 11 LS states 3s23p2 3P, 1D, 1S, 3s3p3 3Do, 3Po 1 Do, 3So, 1Po, 3s23p3d 3Po, 1Do of Fe XIII are considered. The target states are represented by configuration interaction wave functions. Rydberg series of resonances converging to the excited state thresholds are included in the calculation. Present results for collision strengths are compared where possible with available other calculations. Some significant differences are noted. The effective collision strengths are determined assuming a Maxwellian distribution of electron energies. These are listed over the temperature range (5-40) × 105 K.
Relative level populations and the density-sensitive emission-line ratios R1 = I(186.87 Å)/I(193.51 Å), R2 = I(196.64 Å)/I(193.51 Å), and R3 = I(191.05 Å)/I(193.51 Å) are derived using the recent R-matrix calculations of electron impact excitation rates for Fe XII over a wide range of electron densities (109-1012 cm-3) and at an electron temperature of 1.5 × 106 K. These results are applied to solar active region and flare spectra obtained by the Naval Research Laboratory's S082A slitless spectrograph on board Skylab. Excellent agreement is found with observations. The electron densities deduced from Fe XII line ratios are also in agreement with those determined from Fe XII and Fe XIV.
A new, accurate set of electron impact collisional data is presented,
relating to all electric dipole fine-structure transitions between the
ground {3s(2) 3p(3) } and the first two excited {3s 3p(4) }, {3s(2)
3p(2) 3d} configurations in {Fe xii} (Fe(11+) ). Theoretical energies
have been obtained with a multi-configuration atomic structure
calculation. The {R-matrix} method, coupled with the {Coulomb-Bethe}
(CBe) approximation for the high partial wave contributions to the
collision strengths, has been employed in the Fe(11+) - e(-) scattering
problem. The data presented in this paper form part of the IRON Project
effort to provide the most accurate atomic data available to date for
all the iron ions (Hummer et al. 1993). Tables 1 to 9 are also available
in electronic form at the CDS via ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
Multiply-ionized Fe atoms were produced by discharges in a plasma focus apparatus with an Fe electrode in an ambient atmosphere of He, and the discharge condition for the most intense emission from Fe ions was found. The extreme ultraviolet spectrum was photographed under this condition with a grazing incidence spectrograph in the wavelength range between 70 and 500 Å. The spectrum has many strong emission lines in the range from 170 to 200 Å and is very similar to the spectrum of the quiet sun. Lines of FeVIII to XVIII ions are identified in the range between 90 and 210 Å and are tabulated together with the measured relative intensities. The results are discussed in relation to the solar and laboratory plasma spectra so far observed in the extreme ultraviolet range.
High-resolution spectra of the elements Fe, Ni, Zn, Ge, Se, and Mo injected into the Princeton Large Torus tokamak were recorded by the 2-m Schwob--Fraenkel soft-x-ray multichannel spectrometer. Spectra were recorded every 50 msec during the times before and after injection. The spectral lines of the injected element were very strong in the spectrum recorded immediately after injection, and the transitions in the injected element were easily distinguished from the transitions in the intrinsic elements (C, O, Ti, Cr, Fe, and Ni). An accurate wavelength scale was established using well-known reference transitions in the intrinsic elements. The spectra recorded just before injection were subtracted from the spectra recorded after injection, and the resulting spectrum was composed almost entirely of transitions from the injected element. A large number of ..delta..n = 0 transitions between the ground and the first excited configurations in the Li I through K I isoelectronic sequences of the injected elements were identified in the wavelength region 60 to 345 A.
Details of a new computational method for calculating collision strengths are presented through an application to Fe XIII. The method, which enables the computation of collision strengths for complex ions, is adapted from long-established optimization techniques previously used for the calculation of atomic energy levels and oscillator strengths. The procedure involves the adjustment of Slater parameters and average energies of configurations so that they result in improved energy levels and eigenvectors. These improved values can then provide a basis for collision strength calculations in ions where ab initio computations break down or result in unnecessarily large errors. The present application is implemented through modifications of the DISTORTED WAVE collision code and SUPERSTRUCTURE atomic-structure code interfaced via a transformation code JAJOM, which also processes their output; these atomic codes were written at University College London. It should be feasible to make similar adaptations to other collision codes. The Cowan suite of atomic-structure codes generated the optimized parameters. Fe XIII collision strengths are tabulated for 3s²3p²-3s3p³ and 3s²3p²-3s²3p3d transitions. Six configurations, 3s²3p², 3pâ´, 3s²3p3d, 3s3p3d², and 3p³3d, were included in these computations.
Improved atomic data for Ti VI and Fe X are calculated with atomic-structure codes which incorporate Slater parameter optimization. These semiempirical calculations rely on newly reported energy level identifications and measurements in Ti VI, on the basis of which a computational model was established for Ti VI and then applied to compute improved oscillator strengths and predicted energy levels for both Ti VI and Fe X. The Fe X oscillator strengths are needed to aid the interpretation of line intensities in the solar spectrum. Configuration interaction was included between four odd- and seven even-parity configurations. Data for the 3s23p5-3s3p6 transitions were found to be very sensitive to configuration-interaction effects.
Large scale CIV3 calculations of excitation energies from ground state as well as of oscillator strengths and radiative decay rates for all electric–dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to the (1s22s22p6)3s23p2, 3s3p3, 3p4, 3s23p3d, 3s23p4s, 3s23p4p, 3s23p4d and 3s23p4f configurations of Ni XV, are performed using very extensive configuration-interaction wave functions. The relativistic effects in intermediate coupling are incorporated by means of the Breit–Pauli Hamiltonian. In order to keep our calculated energy splittings as close as possible to the National Institute of Standard and Technology (NIST) values, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. Our calculated excitation energies, including their ordering, are in excellent agreement with the available NIST results. From our radiative decay rates we have also calculated radiative lifetimes of the fine-structure levels. It is noted that our calculated radiative rates show significant disagreement (23–30%) with those calculated by Ishikawa and Vilkas (2002 Phys. Scr.65 219) for the transitions involving the 3s3p3(5S2) level. For this high spin level 3s3p3(5S2) our calculated lifetime is found to be in excellent agreement with the experimental value of Träbert et al (1989 Z. Phys. D 11 207). In this calculation, we also predict many additional new and accurate data for various optically allowed and intercombination transitions to complete the void in the existing data.
High resolution spectra of the elements Fe, Mi, Zn, Ge, Se, and Mo injected into the PLT tokamak have been recorded by the 2 meter Schwob-Fraenkel soft x-ray multichannel spectrometer (SOXMOS). Spectra were recorded every 50 ms during the time before and after injection. The spectral lines of the injected element were very strong in the spectrum recorded immediately after injection, and the transitions in the intrinsic elements (mostly Fe, Ti, and Cr). An accurate wavelength scale was established using well-known reference transitions in the intrinsic elements. The spectra recorded after injection, and the resulting spectrum is composed almost entirely of transitions from the injected element. A large number of delta n=0 transitions in the Li I through K I (except Ne I) isoelectronic sequences of the injected elements were identified in the wavelength region 70 A to 345 A. (jhd)
Density-sensitive emission-line ratios R1 = I(338.27 A)/I(364.47 A) and
R2 = I(338.27 A)/I(352.10 A) are calculated for Fe XII using new
electron collisional excitation rates which are substantially larger
than those previously published. Electron densities deduced from the
values of R1 and R2 for solar active regions and flares obtained by the
NRL S082A slitless spectrograph on Skylab are in good agreement.
We present a detailed study of element abundances in the corona of
Procyon based on spectroscopic observations obtained with the Extreme
Ultraviolet Explorer Satellite (EUVE). Emission measures (EMs) have been
derived from observed line fluxes for the elements O, Ne, Mg, Si, S, Ar,
Fe, and Ni, using the most recent atomic data. The slope of the
resulting EM distribution is very similar to the well known result of
1.5 (EM is proportional to T3/2 found for the solar corona
for log T = 5.3-6.0. The abundances in the corona of Procyon are found
to be consistent with their photospheric values. No enhancement of
species with low first ionization potentials (FIPs) is observed, such as
is the case for the solar corona: the 'FIP effect' appears to be absent
in Procyon. We speculate that the dominant emission from the corona and
transition region in Procyon could originate in low-altitude structures
analogous to the solar supergranulation network, which does not appear
to exhibit an FIP effect. A considerable body of observational evidence
suggests both that Procyon is a 'basal' star in terms of its
chromospheric activity and that it is on the spectral type boundary
which separates stars which exhibit activity levels correlated with
rotation and those which do not. Such stars are though by some workers
to sustain coronae which are heated predominantly by acoustic means. We
also note that an acoustically heated outer atmosphere might not possess
sufficiently small structures to support a fractionation of elements
with respect to FIP. Our results demonstrate that the FIP effect is not
an ubiquitous feature of late-type stellar coronae. Consequently,
speculations in the literature that the FIP effect observed in cosmic
rays is a result of their originating from seed particles injected by
late-type stellar coronae must await observational confirmation that the
FIP effect does indeed operate on M dwarfs, which are likely to be the
dominant particle injection source.
We present an analysis of the EUV spectrum of the chromospherically
active star ɛ Eridani (K2 V) recorded by the Extreme-Ultraviolet
Explorer satellite. We have identified many lines from different
elements (0, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni) with first ionization
potential (FIP) above and below about 10 eV (high and low FIP,
respectively) and have used the measured relative intensities of these
to investigate the emission measure (EM) distribution and the coronal
element abundances. The spectrum of E Eri reveals much hotter plasma
than the quiet Sun and, as such, is interesting to compare with EUV
spectra of solar flares. The EM distribution is found to be sharply
peaked near log T = 6.5. The data suggest that a solar-like FIP effect
is in operation, although the limited number of high-FIP lines detected,
together with the sharply peaked shape of the EM distribution and low
signal-to-noise ratio of the spectra, preclude a definitive judgement.
However, we can conclude that there cannot be an enhancement of low-Fl P
species in the corona of ɛ Eri significantly larger than that
seen in the "average" solar corona, which may imply that the magnitude
of the FIP effect does not seem to increase with increasing stellar
activity, but this should be confirmed by other cases.
LS-coupled K matrices calculated in an R-matrix approach are recoupled
to obtain collision strengths for fine-structure transitions within the
ground 3s23p3 configuration in an intermediate
coupling scheme. The target states are represented by extensive
configuration-interaction wave functions. The relativistic effects in
the target are allowed in the Breit-Pauli formulation. The effective
collision strengths are obtained by integrating the collision strengths
over a Maxwellian distribution of electron energies. These are listed
over a wide temperature range (400,000 - 3,000,000K).
The authors have evaluated oscillator strengths for several transitions
between the ground 3s23p3 configuration and the
excited 3s3p4 and 3s23p23d
configurations using fairly large configuration-interaction expansions.
The calculations are performed in both LS and intermediate couplings.
The relativistic effects in intermediate coupling are incorporated by
means of the Breit-Pauli Hamiltonian. Comparison with other available
results is generally good.
We obtained high-resolution extreme-ultraviolet (EUV) spectra of solar
active regions, quiet-Sun areas, and off-limb areas during 1991 May 7
and 1993 August 17 flights of NASA/Goddard Space Flight Center's Solar
EUV Rocket Telescope and Spectrograph (SERTS). The 1991 flight was the
first time a multilayer coated diffraction grating was ever used in
space. Emission lines from the eight ionization stages of iron between
Fe+9 (Fe x) and Fe+16 (Fe XVII) were observed.
Values of numerous density- and temperature-insensitive line intensity
ratios agree with their corresponding theoretical values.
Intensity ratios among various lines originating in a common stage of
ionization provide measurements of coronal electron density. Numerous
density-sensitive ratios are available for Fe xiii, and they yield
active region density (cm-3) logarithms of 9.66±0.49
and 9.60±0.54 for the 1993 and 1991 flights, respectively, and a
quiet-Sun density of 9.03±0.28 for the 1993 flight. Filling
factors, calculated from the derived densities assuming a path length of
1 × 109 cm, range from several thousandths to nearly
unity.
Intensity ratios among lines originating in different ionization stages
of iron yield measurements of coronal electron temperature in the
isothermal approximation. The line ratios yield temperatures ranging
from 1.1 × 106 to 5.2 × 106 K for the active
regions, and 1.0 × 106 to 2.1 × 106 K for the
quiet Sun, depending upon the ionization stages used. The derived
temperature diminishes with decreasing ionization stages. Fe XVII
emission, detected in the active regions but not in the quiet areas,
accounts for the higher maximum active region temperature. Derived
active region temperatures are greater than their quiet-Sun counterparts
for ratios that include lines from Fe xiv through Fe XVI; however, the
derived active region and quiet-Sun temperatures are not statistically
significantly different for line intensity ratios that involve only Fe x
through Fe xiii. The latter similarity in derived temperatures suggests
the presence of similar thermal structures in all the areas observed,
although the active regions also harbor hotter material.
Differential emission measure (DEM) distributions were constructed for
the active region and quiet- Sun observations obtained during both
flights. The two quiet-Sun DEM curves and the 1993 active region DEM
curve all show peaks between log T = 6.1 and 6.2. The 1993 active region
DEM has a second peak between log T = 6.6 and 6.7, and the 1991 active
region DEM has only one peak, between log T = 6.5 and 6.6. Thus, the
1993 active region DEM curve appears, in some sense, to be a composite
of the quiet-Sun DEM curve and the 1991 active region DEM curve. The
1991 active region exhibited flaring activity, yielded higher line ratio
temperatures, and contained greater photo spheric magnetic fields than
the 1993 active region.
Energy levels, oscillator strengths and transition probabilities for transitions among the fine-structure levels of the terms belonging to the 3s23p2, 3s3p3, 3s23p3d, 3p4, 3s23p4s, 3s23p4p, 3s23p4d and 3s23p4f configurations of Ca VII are calculated using extensive configuration-interaction (CI) wavefunctions obtained with the CIV3 (configuration interaction version 3) computer code of Hibbert. The relativistic effects in intermediate coupling are incorporated by means of the Breit–Pauli Hamiltonian which consists of the non-relativistic term plus the one-body mass correction, Darwin term, and spin–orbit, spin–other–orbit, and spin–spin operators. Small adjustments to the diagonal elements of the Hamiltonian matrices have been made, so that the energy splittings are as close as possible to the experimental values. The energy splitting of 70 fine-structure levels, oscillator strengths and transition probabilities for electric-dipole-allowed and intercombination transitions and, also the lifetimes of fine-structure levels are presented and compared with available experimental and other theoretical results. Our calculated fine-structure energies, including their ordering, show excellent agreement (better than 0.5%) with the available experimental results. In this calculation, we also predict new data for several levels where no other theoretical and experimental results are available.
We present an analysis of the EUV spectrum of the nearby binary α Cen AB (G2 V, K0 V), observed by the Extreme Ultraviolet Explorer satellite (EUVE). Emission measure curves are constructed for elements with high and low first ionization potential (FIP) in order to investigate the coronal composition and determine whether or not a solar-like compositional fractionation mechanism ("FIP effect") is operating in the corona of α Cen. As pointed out in the recent analysis of the α Cen EUVE spectra by Mewe et al., the emission measure distribution is very much like that of the Sun. It peaks at log T ~ 6.3, has a minimum near log T ~ 5.5, and has a slope between these points of approximately 1.75 (EM ∝ T7/4). The emission measure results for the different elements are not consistent with the underlying photospheric composition and indicate that the low-FIP elements are overabundant relative to the high-FIP elements by a factor of about 2. This result represents the first evidence of the FIP effect in solar-like stars with similar activity to that of the Sun.
We also discuss the recently raised possibility that resonant scattering of line radiation might be important in EUV stellar spectra like that of α Cen. We conclude that this is unlikely and that the results of global plasma model-fitting techniques that have engendered this hypothesis have not taken into account the flux from spectral lines that are missing from current models of plasma radiative loss.
This review of recent contributions to the classification of the spectra of highly ionised atoms emphasises how major research projects have influenced progress. These projects include experiments on board orbiting space satellites and SKYLAB, those of fusion research (notably involving TOKAMAK devices), studies with giant pulse laser-produced-plasmas and beam-foil spectroscopy. In addition, the large volume of data gathered through the application of traditional methods and the impact of theoretical calculations are discussed. A comprehensive reference list of papers reporting emission line identifications for elements lighter than nickel and ionisation stages higher than the fourth is included, along with references to other bibliographies and compilations of energy levels, or wavelengths and identifications.
Electron collisional excitation strengths for transitions among the fine-structure levels of the ground 3s23p2 configuration and from the levels of 3s23p2 configuration to the levels of the excited 3s3p3 and 3s23p3d configurations in Fe XIII are calculated using a semirelativistic R-matrix approach. We considered 14 LS 3s23p23P,1D,1S, 3s3p33Do,3Po,1Do,3So,1Po, 3s23p3d3Po,1Do,3Do,3Fo,1Fo, and 1Po states of Fe XIII in the present calculation. The 14 LS states give rise to 26 fine-structure levels that are represented by configuration-interaction wave functions. The relativistic effects are included in the Breit-Pauli approximation via one-body mass correction, Darwin, and spin-orbit interaction terms in the scattering equations. Complicated resonance structures are explicitly included in the collision strengths. The collision strengths are integrated over a Maxwellian distribution of electron energies to give effective collision strengths over a wide temperature range from 5 × 105 to 5 × 106 K.
The HXR self-consistent field calculations of wavelengths and transition probabilities previously reported along the silicon sequence for elements K to Ti are extended to the 3s-3p and 3p-3d transitions of elements V to Ni. Ab initio HXR values of Slater parameters have been adjusted by a leastsquare optimization process of the calculated eigenvalues of the Hamiltonian with the available experimental energy levels. New accurate wavelengths and transition probabilities have been derived and six new identifications of solar lines are proposed.
Relativistic quantum defect orbital (RQDO) calculations have been performed with and without taking explicit account of the core-valence correlation of oscillator strengths for the dipole-allowed fine-structure 3p3 4So-3p2(3P)3d 4P transition array of a number of P-like ions (Cl III-La XLIII). The present f-values are analysed on the basis of other theoretical data available in the literature. Regularities in the transition intensities along the isoelectronic sequence for each line of the multiplet are also tested.
New calculations of transition probabilities are presented for forbidden lines in the ground configuration of the phosphorus sequence from Ar to Ru. Relativistic contributions and configuration interaction effects were included in the framework of the HXR and HFR self-consistent-field methods. Energy levels and A values were computed in intermediate coupling with fitted or interpolated semi-empirical energy parameters. The variation in magnetic dipole and electric quadrupole oscillator strengths as a function of Z is extended beyond nickel to Z = 44.
Satellite lines are identified in the X-ray spectrum of foil-excited fast silicon ions. These lines result from transitions from levels of principal quantum number n: up to n=6 in He-like Si XIII, up to n=5 in Li-like Si XII, and up to n=3 in Si XI, Si X, Si IX and Si VIII. The identifications are made with the aid of theoretical 'Hartree-XR' atomic-structure calculations of energy levels and oscillator strengths.
Wavelengths and oscillator strengths for the 2s22p5-2s22p44d, 4s electric-dipole transitions in fluorine-like ions from copper to arsenic have been calculated using Cowan and Griffin's HXR method (1970) and Slater-Condon theory (1978). Configuration mixing effects have been considered in detail. The predictions are compared with experimental spectra of copper, zinc, gallium and arsenic, obtained by focusing 30 GW laser pulses on to planar targets. The spectra were recorded with a convex-crystal X-ray spectrograph, and lines measured with accuracies of +or-2 to +or-5 mAA are identified with the stronger 2p-4d and 2p-4s transitions.
The 3s23p2 3P-3s3p3 5So intercombination lines in the silicon isoelectronic sequence have been observed for Si I-S III only. By combining ab initio calculations with isoelectronic trend analyses we have obtained predicted values for the 5S2o energy and wavelengths of the intersystem lines in Cl IV-Ni XV. The mixing of the 5S2o level with the triplet levels of the same configuration has been studied in detail. Theoretical results are given for the 5S2o lifetime and the relative intensity of the two intercombination lines. The results are compared with recent MCDF calculations of Huang.
The long history of the theory of complex atomic spectra, as distinct from series spectra, is reviewed from the period of the 1930s, when quantum mechanics was rapidly applied to solve a variety of problems, to the present day, when, at a single stroke, elaborate computer programs are used to fit many hundreds of atomic energy levels to theoretical models. Emphasis is placed on the use of of annihilation and creation operators. With their help, the role that Lie groups play in atomic spectra can be described in analogy to SO(3), the special orthogonal group corresponding to rotations in ordinary three-dimensional space. Configuration interaction is represented by effective operators that act within the states of the unperturbed configuration under study. These effective operators are also usefully constructed from annihilation and creation operators. A table is given in which the least-squares fits to the levels of atomic configurations comprising at least three electrons (or electron holes and electrons) are listed.
Emission lines of krypton IV and V belonging to the 4s24pq-4s24pq-14d and 4s24pq-4s4pq+1 transition arrays are classified with the aid of a theoretical model developed for analogous Fe XII and Fe XIII transitions in a different atomic shell. Xenon VI lines are also identified. The observational material consisted of archived Zeta spectrograms.
Calculated oscillator strengths are listed for 2s2 2p5 - 2s 2p6, 2s2 2p5 - 2s2 2p4ns, 2s2 2p5 - 2s2 2p4nd and for 2s2 2p4nl - 2s2 2p4n'l' (l = s, p; l' = p, d; n, n' = 3, 4) transitions of Mg IV.
They have been computed with the aid of a HXR computer program, initially developed by Cowan [18], including configuration interaction and some relativistic effects. Ab initio values of Slater radial energy integrals have been adjusted by a non-linear least-square optimization routine, using the available experimental energy levels.