Previous computations of low-temperature Rosseland and Planck mean opacities from Alexander & Ferguson areupdatedandexpanded.Thenewcomputationsincludeamorecompleteequationofstate(EOS)withmoregrain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the EOS calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high-temperature condensates such as Al2O3 and CaTiO3 significantly affects the total opacityoveranarrowrangeoftemperaturesbeforetheappearanceofthefirstsilicategrains.Thenewopacitytables are tabulated for temperatures ranging from 30,000 to 500 K with gas densities from 10 � 4 to 10 � 19 gc m � 3 .C omparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method is shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided. Subject heading gs: atomic data — equation of state — methods: numerical — molecular data

http://iopscience.iop.org/article/10.1086/428642/pdf

Low-temperature opacities

A Calculation of Atomic Structures. By D. R. Hartree Pp. xiii, 181. 40s. 1957. (Wiley, New York)

Collisional alignment and orientation of atomic outer shells I. Direct excitation by electron and atom impact

A review of the quantum theory of ionizing collisions is presented, with particular regard to recent theoretical developments. A discussion is given of quantal and classical approximations and their predictions compared with experimental data. Some useful empirical formulas are listed and compared, and in conclusion mention is made of the present inadequacies in the theory.

Theory of the ionization of atoms by electron impact.

Dielectronic recombination is a process particularly effective in high-temperature dilute plasmas such as those observed, for example, in astrophysics. This process was first recognised for its noticeable effects on the establishment of ionisation equilibrium in the solar corona. Over the last decade, its importance as a line formation mechanism has been emphasised. It is responsible for spectral lines appearing as satellites to the long-wavelength side of the resonance lines of the highly ionised systems typical of hot plasmas. However, in transient ionising plasmas and for the heavier ions these lines can also be produced by direct excitation of an inner-shell electron. This review is concerned essentially with the analysis and interpretation of the satellite lines in terms of the physical parameters characterising the emitting plasma. Extensive results concerning the astrophysically important hydrogen-like and helium-like ions are summarised. These are compared with the few available high-resolution soft X-ray spectra of solar active regions and flares.

http://iopscience.iop.org/article/10.1088/0034-4885/43/2/002/pdf

Dielectronic recombination and its applications in astronomy

A polarized orbital distorted wave model is used to calculate total and differential cross sections for 1s to ns(n=2,3,4,5) electron impact induced transitions in H and He+ from threshold to 20 Ryd. The total cross sections for the 1s to 2s transitions are in good agreement with experiment, but cannot in this model show resonances. The differential cross sections at energies above 100 eV agree closely with those of Geltman and Hidalgo (1971). The model reduces to the Born-Oppenheimer (z=0) or CBO I(z=0) when the polarization and static potentials are omitted.

https://iopscience.iop.org/article/10.1088/0022-3700/6/8/022/pdf

Electron impact excitation of H and He+. I. 1s to ns transitions

A unitarised distorted-wave polarised-orbital model is used to investigate electron impact excitation of the Li, Na and K resonance transitions at low and intermediate energies. Results are presented for integral (total) cross sections, differential cross sections, coincidence parameters, and, for K, spin-flip differential cross sections. They are compared where possible with experiment and other theoretical models. The evaluation of the adiabatic polarisation interaction is discussed. Core-exchange effects are investigated for the case of Na. Tables of T-matrix elements are available for all three cases to aid in interpretation of photon-electron coincidence experiments.

Electron impact excitation of the resonance transitions of Li, Na and K

Calculations are reported on the electron impact excitation of the n1P (n=2,3,4,5) states of He from the ground state. The incident energy range covered is from threshold to 500 eV, and the calculations are carried out in the distorted-wave polarized-orbital model. Total cross sections for all n<or=5, total differential cross sections differential cross sections for individual magnetic sub-levels, and orientation and alignment parameters for n=2,3 are presented and compared with other theoretical studies and with experiment. Excitation of He (23P) is briefly discussed.

https://iopscience.iop.org/article/10.1088/0022-3700/9/13/011/pdf

Electron impact excitation of the n1P(n=2-5) and 23P states of helium at intermediate energies

For pt. I see ibid., vol. 6, 1435 (1973). Coupling terms which were previously omitted are retained in a distorted wave polarized orbital calculation of electron impact excitation of the 1s to 2s transition in H and He+. The results for H are in very good agreement with the best close coupling results are low energies. For He+ the previous results are reduced by 18% at threshold, and fall 50% below experiment there.

Electron impact on H and He+. II. Coupling effect in the distorted wave polarized orbital approximation

For pt.V see ibid., vol.8, p.1073 (1975). Electron impact excitation of the n=3 levels of atomic hydrogen is investigated by generalizing the DWPO II approximation (McDowell et al.) to 1s to nlml transitions. Results are presented, at energies from threshold to 500 eV, for total cross sections for each 1s to 3l (l=0,1,2) transition, total n=3 cross sections, and the cross section for H alpha production. They are compared, where possible, with experiment. Results for the polarization of H alpha emitted at 90 degrees to the incident beam are given in Born and DWPO II models, and shown to be inconsistent with experiment. Differential cross sections for individual and total n=3 transitions are tabulated at selected angles and energies. Further experimental and theoretical work is suggested.

M R C McDowell

Papers

Electron impact excitation of H and He+. I. 1s to ns transitions

Electron impact excitation of the resonance transitions of Li, Na and K

Electron impact excitation of the n1P(n=2-5) and 23P states of helium at intermediate energies

Electron impact on H and He+. II. Coupling effect in the distorted wave polarized orbital approximation

Electron impact excitation of H and He+. VI. Excitation of the n=3 levels