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K A Berrington

Bio: K A Berrington is an academic researcher from Sheffield Hallam University. The author has contributed to research in topics: Excited state & Electron excitation. The author has an hindex of 20, co-authored 54 publications receiving 1556 citations.


Papers
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Journal ArticleDOI
TL;DR: A detailed description of the methods being used in a collaborative effort which is referred to as the Opacity Project is given in this article, where the close-coupling approximation of electron-atom collision theory is used to calculate energies and wavefunctions for bound states, oscillator strengths, photoionisation cross sections and parameters for line broadening by electron impact.
Abstract: For pt.I see ibid., vol.20, p.6363-78 (1987). A general description of the data requirements for opacity calculations has been given in paper I. The present paper gives a detailed description of the methods being used in a collaborative effort which is referred to as the Opacity Project. The close-coupling approximation of electron-atom collision theory is used to calculate energies and wavefunctions for bound states, oscillator strengths, photoionisation cross sections and parameters for line broadening by electron impact. The computations are made using the R-matrix method together with new codes for calculating outer-region solutions and dipole integrals. Use of these techniques provides an efficient means of calculating large amounts of accurate atomic data.

427 citations

Journal Article
TL;DR: The IRON project as mentioned in this paper aims to compute electron excitation cross sections and rates of astrophysical and technological importance using the most reliable procedures currently available, e.g. from the Opacity Project.
Abstract: 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

160 citations

Journal ArticleDOI
TL;DR: In this article, the available experimental and atomic data for ( configurations) are reviewed and assessed, and new collisional and radiative data are calculated to supplement published data, with empirical adjustements that take into account observed wavelengths.
Abstract: This is the first in a series of papers in which we benchmark recent atomic data available for astrophysical applications. We review various issues related to the completeness and accuracy of both theoretical and experimental data. In this paper, the available experimental and atomic data for ( configurations) are reviewed and assessed. New collisional and radiative data are calculated to supplement published data. The radiative calculations are done with empirical adjustements that take into account observed wavelengths. Previous line identifications are also reviewed and assessed. Our approach focuses on the brightest spectral lines, and uses both wavelengths and line intensities to assess the line identifications on a quantitative basis. Although many previous line identifications are confirmed, some are rejected (e.g. the coronal line observed at 1582.35 A). We confirm previously suggested identifications (e.g. 257.262 A, 1028.02 A), and we present new ones, (e.g. the lines of the 3s2 3p4 3d–3s 3p5 3d transition array). In addition, we highlight the presence of blends and we review which spectral lines are best for density diagnostics or for instrument calibration. The theoretical data (line intensities and level lifetimes) are benchmarked against well-calibrated spectroscopic observations of the solar corona and laboratory measurements. The agreement between theoretical and experimental data which we achieve with our new model ion is very good.

108 citations

Journal Article
TL;DR: A general description of the methods used by the participants in the international Opacity Project to produce massive sets of accurate radiative atomic data, followed by some illustrative examples of results obtained is given in this article.
Abstract: A general description is given of the methods used by the participants in the international Opacity Project to produce massive sets of accurate radiative atomic data, followed by some illustrative examples of results obtained

105 citations

Journal ArticleDOI
TL;DR: In this paper, atomic data are used in conjunction with the statistical equilibrium code of Dufton (1977) to calculate relative C III and Si III level populations, and hence emission-line strengths for a range of electron temperatures and densities.
Abstract: Atomic data are used in conjunction with the statistical equilibrium code of Dufton (1977) to calculate relative C III and Si III level populations, and hence emission-line strengths for a range of electron temperatures and densities. It is assumed that photoexcitation and deexcitaton rates are negligible in comparison with the corresponding collisional rates, that ionization to and recombination from other ionic levels are slow compared with bound-bound rates, and that all transitions are optically thin. The observed values of R1 and R2 for several planetary nebulae and a symbiotic star, measured from high-resolution spectra obtained with the IUE satellite, lead to electron densities that are compatible, and are also in good agreement with those deduced from line ratios in other species.

71 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84.
Abstract: CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission‐line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.

2,571 citations

Journal ArticleDOI
TL;DR: In this article, an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, is presented.
Abstract: Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 104 model atmospheres for stars with 2500K <= T-eff <= 8000 K, -1 <= log g = log (GM/R-2) <= 5 (cgs) with various masses and radii, -5 <= [Me/H] <= + 1, with [alpha/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This includes "CN-cycled" models with C/N=4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 <= xi(t) = 5km s(-1). We also list thermodynamic quantities (T, P-g, P-e, rho, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.

2,411 citations

Book
09 Jan 2011
TL;DR: In this paper, a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium is presented, including 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.
Abstract: 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)

1,143 citations

Journal ArticleDOI
TL;DR: In this article, the authors review possible systematic errors in studies of F-, G- and K-type stars introduced by these questionable approximations and discuss the most vulnerable species and low-excitation transitions.
Abstract: ▪ 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...

755 citations

Journal ArticleDOI
TL;DR: RMATRX1 as mentioned in this paper is a general program to calculate atomic continuum processes using the R -matrix method, including electronatom and electron-ion scattering, and radiative processes such as bound-bound transitions, photoionization and polarizabilities.

679 citations