Quantum defect theory (QDT) is concerned with the properties of an electron in the field of a positive ion and, in particular, with expressing those properties in terms of analytical functions of the energy. It provides a unified theory of bound states, including series perturbations, autoionisation and electron-ion scattering, both elastic and inelastic. The main emphasis of the review is on the foundations of the theory. Properties of Coulomb functions are discussed in some detail and outline sketches are given of relevant topics in collision theory and radiative theory. One-channel and many-channel QDT are discussed separately. Applications to the following problems are considered: resonances, atomic collision calculations, systems with two energy levels of the ion core, helium, other rare gases, alkaline earths and other atomic systems, molecular hydrogen, dielectronic recombination.

https://iopscience.iop.org/article/10.1088/0034-4885/46/2/002/pdf

Quantum defect theory

▪ Abstract The information on the chemical compositions of stars encoded in their spectra plays a central role in contemporary astrophysics. Stellar element abundances are, however, not observed: to decipher the spectral fingerprints in terms of abundances requires realistic models for the stellar atmospheres and the line-formation processes. Still today, the vast majority of abundance analyses of late-type stars rely on one-dimensional (1D), hydrostatic model atmospheres and the assumption of local thermodynamic equilibrium (LTE). In this review possible systematic errors in studies of F-, G- and K-type stars introduced by these questionable approximations are discussed. Departures from LTE are commonplace and often quite severe, in particular for low surface gravities or metallicities, with minority species and low-excitation transitions being the most vulnerable. Recently, time-dependent, 3D, hydrodynamical model atmospheres have started to be employed for stellar abundance purposes, with large differe...

New light on stellar abundance analyses: Departures from LTE and homogeneity.

RMATRX1: Belfast atomic R-matrix codes

Aims. The goal of the CHIANTI atomic database is to provide a set of atomic data for the interpretation of astrophysical spectra emitted by collisionally dominated, high temperature, optically thin sources. Methods. A complete set of ground level ionization and recombination rate coefficients has been assembled for all atoms and ions of the elements of H through Zn and inserted into the latest version of the CHIANTI database, CHIANTI 6. Ionization rate coefficients are taken from the recent work of Dere (2007, A&A, 466, 771) and recombination rates from a variety of sources in the literature. These new rate coefficients have allowed the calculation of a new set of ionization equilibria and radiative loss rate coefficients. For some ions, such as Fe viii and Fe ix, there are significant differences from previous calculations. In addition, existing atomic parameters have been revised and new atomic parameters inserted into the database. Results. For each ion in the CHIANTI database, elemental abundances, ionization potentials, atomic energy levels, radiative rates, electron and proton collisional rate coefficients, ionization and recombination rate coefficients, and collisional ionization equilibrium populations are provided. In addition, parameters for the calculation of the continuum due to bremsstrahlung, radiative recombination and two-photon decay are provided. A suite of programs written in the Interactive Data Language (IDL) are available to calculate line and continuum emissivities and other properties. All data and programs are freely available at http://wwwsolar.nrl.navy.mil/ chianti

/pdf/chianti-an-atomic-database-for-emission-lines-ix-ionization-3qbi17r7xq.pdf

CHIANTI - an atomic database for emission lines. IX. Ionization rates, recombination rates, ionization equilibria for the elements hydrogen through zinc and updated atomic data

▪ Abstract Broad emission lines hold fundamental clues about the kinematics and structure of the central regions in AGN. In this article we review the most robust line profile properties and correlations emerging from the best data available. We identify fundamental differences between the profiles of radio-quiet and radio-loud sources as well as differences between the high- and low-ionization lines, especially in the radio-quiet majority of AGN. An Eigenvector 1 correlation space involving FWHM Hβ, W(FeIIopt)/W(Hβ), and the soft X-ray spectral index provides optimal discrimination between all principal AGN types (from narrow-line Seyfert 1 to radio galaxies). Both optical and radio continuum luminosities appear to be uncorrelated with the E1 parameters. We identify two populations of radio-quiet AGN: Population A sources (with FWHM(Hβ) 4000 km s−1, generally strong FeII emission and a soft X-ray excess) show almost no parameter space overlap with radio-loud sources. Population B shows optical properties...

Phenomenology of Broad Emission Lines in Active Galactic Nuclei

The IRON Project has the goal of computing on a large scale electron excitation cross sections and rates of astrophysical and technological importance, using the most reliable procedures currently available. Radiative transition probabilities and photoionization cross sections not known from other sources e.g. from the Opacity Project, will also be presented. Although the major effort will be for ions of the iron-group elements, other ions of astrophysical interest will also be included. In this introductory paper models and procedures to be used are summarized and the approximations are discussed. As an example of our computational procedures, typical results for fine structure transitions involving electron collisions with Fe XVIII ions and radiative data from Fe XVII are presented

Atomic data from the IRON project. I. Goals and methods.

Based on new calculations, we reconfirm the low- and high-density limits on the forbidden finestructure line intensity ratio [O II] I (3729)/I (3726) : limNe→0 = 1.5 and limNe→∞ = 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, and validate the extensive observational analyses of gaseous nebulae by Copetti & Writzel and Wang et al. that reach the same conclusions. The present theoretical results and the recent observational analyses differ significantly from the calculations by McLaughlin & Bell and Keenan et al. The new Maxwellian averaged effective collision strengths are presented for the 10 transitions among the first five levels to enable computations of [O II] line ratios.

[O ii] line ratios

An extensive set of fine structure levels and corresponding transition probabilities for allowed and forbidden transitions in Fe xvii is presented. A total of 490 bound energy levels of Fe xvii of total angular momenta $0 \leq J \leq 7$ of even and odd parities with $2 \leq n\leq 10$, $0 \leq l\leq 8$, $0 \leq L\leq 8$, and singlet and triplet multiplicities, are obtained. They translate to over $2.6\times 10^4$ allowed (E1) transitions that are of dipole and intercombination type, and 2312 forbidden transitions that include electric quadrupole (E2), magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type representing the most detailed calculations to date for the ion. Oscillator strengths  f , line strengths  S , and coefficients  A of spontaneous emission for the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix approximation. A -values for the forbidden transitions are obtained from atomic structure calculations using codes SUPERSTRUCTURE and GRASP. The energy levels are identified in spectroscopic notation with the help of a newly developed level identification algorithm. Nearly all 52 spectroscopically observed levels have been identified, their binding energies agreeing within 1% with our calculation. Computed transition probabilities are compared with other calculations and measurement. The effect of 2-body magnetic terms and other interactions is discussed. The present data set enhances by more than an order of magnitude the heretofore available data for transition probabilities of Fe xvii.

/pdf/atomic-data-from-the-iron-project-liii-relativistic-allowed-1a3kh3cl15.pdf

Atomic data from the Iron Project LIII. Relativistic allowed and forbidden transition probabilities for Fe XVII

Atoms in astrophysics.

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.

/pdf/improved-collision-strengths-and-line-ratios-for-forbidden-o-50w9t5dy51.pdf

Werner Eissner

Papers

Atomic data from the IRON project. I. Goals and methods.

[O ii] line ratios

Atomic data from the Iron Project LIII. Relativistic allowed and forbidden transition probabilities for Fe XVII

Atoms in astrophysics.

Improved collision strengths and line ratios for forbidden [O iii] far-infrared and optical lines