Keith A. Berrington

Bio: Keith A. Berrington is an academic researcher from Queen's University Belfast. The author has contributed to research in topics: Electron excitation & Ground state. The author has an hindex of 28, co-authored 77 publications receiving 3288 citations.

Atomic data for opacity calculations. XIV. The beryllium sequence

Abstract: The authors have calculated 1814 energy levels in LS coupling, 33030 oscillator strengths and 859570 photoionization cross section values for the following fifteen members of the beryllium isoelectronic sequence: Be I, B II, C III, N IV, O V, F VI, Ne VII, Na VIII, Mg IX, Al X, Si XI, S XIII, Ar XV, Ca XVII and Fe XXIII. Photoionization is from 1554 bound states lying below the 2s ionization thresholds. The continua are perturbed by resonances converging onto the 2p, 3s, 3p and 3d states of the residual Li-like ions. They delineate the resulting autoionization features by using sufficiently small energy step lengths in regions where the cross sections vary rapidly. Photoexcitation of the core produces large PEC resonances which dominate photoionization of Be I and the less highly ionized ions. They discuss some selected examples drawn from the entire data set and make comparisons with the work of other investigators.

The elastic scattering of electrons from inert gases. III. Argon

Abstract: The R-matrix calculations of O'Malley et al are simplified and extended to the intermediate impact energy range in which the He ground-state wavefunction is coupled with a 'P pseudo-state to include the full static dipole polarisability. Phaseshifts, differen- tial, integrated and momentum transfer cross sections for electrons elastically scattered from helium are reported for the impact energy range of 5 to 200 eV. At low energies the present calculation essentially reproduces the results of O'Malley et a1 for 5 E G 16.5 eV. At intermediate energies good agreement between the present calculations and the most recent measurements is observed.

CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra

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.

An atomic and molecular database for analysis of submillimetre line observations

Abstract: Atomic and molecular data for the transitions of a number of astrophysically interesting species are summarized, in- cluding energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients. Available collisional data from quantum chemical calculations and experiments are extrapolated to higher energies (up to E/k ∼ 1000 K). These data, which are made publically available through the WWW at http://www.strw.leidenuniv.nl/∼moldata, are essential input for non-LTE line radiative transfer programs. An online version of a computer program for performing statistical equilibrium calcu- lations is also made available as part of the database. Comparisons of calculated emission lines using different sets of collisional rate coefficients are presented. This database should form an important tool in analyzing observations from current and future (sub)millimetre and infrared telescopes.

The flexible atomic code

Abstract: 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...

A Grid of Non-LTE Line-blanketed Model Atmospheres of O-Type Stars

Abstract: We have constructed a comprehensive grid of 680 metal line-blanketed, non-LTE, plane-parallel, hydrostatic model atmospheres for the basic parameters appropriate to O-type stars. The OSTAR2002 grid considers 12 values of effective temperatures, 27; 500 KTeff � 55; 000 K with 2500 K steps, eight surface gravities, 3:0 � log g � 4:75 with 0.25 dex steps, and 10 chemical compositions, from metal-rich relative to the Sun to metal-free. The lower limit of log g for a given effective temperature is set by an approximate location of the Eddington limit. The selected chemical compositions have been chosen to cover a number of typical environments of massive stars: the Galactic center, the Magellanic Clouds, blue compact dwarf galaxies like I Zw 18, and galaxies at high redshifts. The paper contains a description of the OSTAR2002 grid and some illustrative examples and comparisons. The complete OSTAR2002 grid is available on-line. Subject headings: methods: numerical — radiative transfer — stars: atmospheres — stars: early-type