New X-ray observatories (Chandra and XMM-Newton) are providing a wealth of high-resolution X-ray spectra in which hydrogen- and helium-like ions are usually strong features. We present results from a new collisional-radiative plasma code, the Astrophysical Plasma Emission Code (APEC), which uses atomic data in the companion Astrophysical Plasma Emission Database (APED) to calculate spectral models for hot plasmas. APED contains the requisite atomic data such as collisional and radiative rates, recombination cross sections, dielectronic recombination rates, and satellite line wavelengths. We compare the APEC results to other plasma codes for hydrogen- and helium-like diagnostics and test the sensitivity of our results to the number of levels included in the models. We find that dielectronic recombination with hydrogen-like ions into high (n = 6-10) principal quantum numbers affects some helium-like line ratios from low-lying (n = 2) transitions.

https://iopscience.iop.org/article/10.1086/322992/pdf

Collisional Plasma Models with APEC/APED: Emission-Line Diagnostics of Hydrogen-like and Helium-like Ions

This is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium--the gas and dust, as well as the electromagnetic radiation, cosmic rays, and magnetic and gravitational fields, present between the stars in a galaxy and also between galaxies themselves. Topics include radiative processes across the electromagnetic spectrum; radiative transfer; ionization; heating and cooling; astrochemistry; interstellar dust; fluid dynamics, including ionization fronts and shock waves; cosmic rays; distribution and evolution of the interstellar medium; and star formation. While it is assumed that the reader has a background in undergraduate-level physics, including some prior exposure to atomic and molecular physics, statistical mechanics, and electromagnetism, the first six chapters of the book include a review of the basic physics that is used in later chapters. This graduate-level textbook includes references for further reading, and serves as an invaluable resource for working astrophysicists. * Essential textbook on the physics of the interstellar and intergalactic medium * Based on a course taught by the author for more than twenty years at Princeton University * Covers radiative processes, fluid dynamics, cosmic rays, astrochemistry, interstellar dust, and more * Discusses the physical state and distribution of the ionized, atomic, and molecular phases of the interstellar medium * Reviews diagnostics using emission and absorption lines * Features color illustrations and detailed reference materials in appendices * Instructor's manual with problems and solutions (available only to teachers)

Physics of the Interstellar and Intergalactic Medium

We describe a complete software package for the computation of various atomic data such as energy levels; radiative transition; collisional excitation; ionization by electron impact, photoionizatio...

The flexible atomic code

Atomic Spectra Database

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

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

RMATRX1: Belfast atomic R-matrix codes

Magnetic dipole transitions between the levels of ground $4{d}^{N}$ configurations of tungsten ions were analyzed by employing a large basis of interacting configurations. Previously introduced configuration interaction strength between two configurations was used to determine the configurations with the largest contribution to wave functions of atomic states for the considered configurations. Collisional-radiative modeling was performed for the levels of the ground configuration coupled through electric dipole transitions with $4{p}^{5}4{d}^{N+1}$ and $4{d}^{N\ensuremath{-}1}4f$ configurations. New identification of some lines observed in the electron-beam ion trap plasma was proposed based on calculations in which wavelength convergence was reached.

Magnetic dipole transitions in 4 d N configurations of tungsten ions

Context Considerable demand exists for electron excitation data for Ni ii, since lines from this abundant ion are observed in a wide variety of laboratory and astrophysical spectra The accurate theoretical determination of these data can present a significant challenge however, due to complications arising from the presence of an open 3d-shell in the description of the target ion Aims In this work we present collision strengths and Maxwellian averaged effective collision strengths for the electron-impact excitation of Ni ii Attention is concentrated on the 153 forbidden fine-structure transitions between the energetically lowest 18 levels of Ni ii E ffective collision strengths have been evaluated at 27 individual electron temperatures ranging from 30–100 000 K To our knowledge this is the most extensive theoretical collisional study carried out on this ion to date Methods The parallel R-matrix package RMATRX II has recently been extended to allow for the inclusion of relativistic effects This suite of codes has been utilised in the present work in conjunction with PSTGF to evaluate collision strengths and effective collision strengths for all of the low-lying forbidden fine-structure transitions The following basis configurations were included in the target model – 3d 9 ,3 d 8 4s, 3d 8 4p, 3d 7 4s 2 and 3d 7 4s4p – giving rise to a sophisticated 295 jj-level, 1930 coupled channel scattering problem Results Comprehensive comparisons are made between the present collisional data and those obtained from earlier theoretical evaluations While the effective collision strengths agree well for some transitions, significant discrepancies exist for others

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Electron-impact excitation of Fe II. Collision strengths and effective collision strengths for low-lying fine-structure forbidden transitions.

The Dirac R-matrix theory is used to calculate the collision strengths for electron impact excitation of He-like ions (S14+, Ca18+ and Fe24+) using the Dirac atomic R-matrix code, which has been developed mainly by Norrington and Grant (Norrington P H and Grant I P 1987 J. Phys. B: At. Mol. Phys. 20 4869). The lowest 31 target levels are included in the calculation. Rate coefficients are obtained for transitions from the ground 1s2 1S0 state to the fine-structure levels of all excited states of 1s2l (l = 0,1) and 1s3l (l = 0,1,2) configurations. We compare our results for rate coefficients with the results of previous calculations, and indicate where significant differences arise because of our more accurate representation of resonance and relativistic effects.

P. H. Norrington

Papers

RMATRX1: Belfast atomic R-matrix codes

Magnetic dipole transitions in 4 d N configurations of tungsten ions

Electron-impact excitation of Fe II. Collision strengths and effective collision strengths for low-lying fine-structure forbidden transitions.

Rate coefficients for electron impact excitation of helium-like ions within the Dirac R-matrix approach

Radiative Rates for Allowed Transitions in Ni-Like Nd, Sm, Eu, Ta, and W