Ronald J. W. Henry

Excitation of atomic positive ions by electron impact

Abstract The current state of theory and its application to excitation of atomic positive ions by electron impact are reviewed. Results of calculations are compared with existing experimental measurements.

A general program to calculate atomic continuum processes using the niem method

Abstract This paper describes a set of computer program packages NIEM which enable electron-atom and electron-ion collision cross sections to be calculated for a general atomic system described by LS -coupling. The calculations are based on a non-iterative integral equation method.

Effective collision strengths for electron impact excitations in S II. [Plasma torus of Io]

Electron impact collision strengths for forbidden, semiforbidden, and allowed transitions in S II calculated using the R-matrix method are presented. Configuration interaction wave functions are used to represent the six target states included in the calculation. At low impact energies the collision strengths are dominated by resonances for several transitions. The contribution from higher partial waves is obtained in the close-coupling approximation with exchange terms omitted. Results are presented for the effective collision strengths over a wide temperature range (5000-150,000 K) of astrophysical interest. The present results for the 4S(0) yields 2P(0) transition are 20-30 percent lower than previous calculations, while for the 4S(0) yields 2D(0) transition they are in good agreement. The results are approximately 30 percent higher than those of Ho and Henry (1983) for the 4S(0) yields 2P(0) transition at 80,000 K, and the difference between the two results increases with decreasing temperatures (under 80,000 K). 38 references.

Oscillator Strengths for S I, S II, and S III

Recent theoretical calculations of oscillator strengths for dipole allowed transitions of S I, S II, and S III are reviewed.

HYDROGEN SPECTRUM IN MAGNETIC WHITE DWARFS : H ALPHA, H BETA AND H GAMMA TRANSITIONS.

Using the results of an accurate variational calculation, the authors present a graphical display of the wavelengths of the Hα, Hβ and Hγ lines of hydrogen, for magnetic-field values ranging from 0 to 560 megagauss, which is believed to cover the range of fields found in magnetic white dwarfs. This is the first complete detailed compilation of such results.

PHOTOIONIZATION CROSS-SECTIONS FOR ATOMS AND IONS OF ALUMINUM, SILICON, AND ARGON.

Photoionization cross sections for all levels belonging to the configurations of atoms and ions of aluminum, silicon, and argon have been calculated using Hartree-Fock bound-electron wave functions and close-coupling approximation free-electron wave functions. The results are presented in the form of a computationally convenient interpolation formula and should find wide astrophysical application.

Fe XII line ratios in solar flares

Relative level populations and the density-sensitive emission-line ratios R 1 = I(186.87 A)/I(193.51 A), R 2 = I(196.64 A)/I(193.51 A), and R 3 = I(191.05 A)/I(193.51 A) are derived using the recent R-matrix calculations of electron impact excitation rates for Fe XII over a wide range of electron densities (10 9 -10 12 cm -3 ) and at an electron temperature of 1.5 × 10 6 K. These results are applied to solar active region and flare spectra obtained by the Naval Research Laboratorys S082A slitless spectrograph on board Skylab. Excellent agreement is found with observations. The electron densities deduced from Fe XII line ratios are also in agreement with those determined from Fe XIII and Fe XIV.

The Fe xii 195.1 Å/1242 Å emission line ratio in the solar corona

Recent R-matrix calculations of electron impact excitation rates in Fe xii are used to derive the theoretical emission line ratio R1 = I(195.1 Å)/I(1242 Å), which is potentially a useful electron density diagnostic for the solar inner corona (r ≤ 1.05 61-01). These results are found to be significantly different from the earlier estimates of Withbroe and Raymond (1984), but are in good agreement with the observed values of R1, for the quiet Sun and an active region. Adoption of the R-matrix atomic data for the 1242 Å line in the coronal iron abundance determination removes an existing discrepancy between results derived from the EUV transition and other iron lines in the solar XUV spectrum. The R-matrix calculations confirm the prediction of Withbroe and Raymond that the earlier discrepancies in R1 and the iron abundance were due to the 1242 Å line excitation rates being underestimated by a factor of ~2. Withbroe and Raymonds paper is, therefore, an excellent example of how astronomical observations can be used to accurately predict atomic physics data.

Electron density diagnostics for Fe XII in the solar plasma

La densite electronique de Fe XII dans le plasma solaire est etudiee a partir des rapports I (338.27 A)/I (364.47 A) et I (338.27 A)/I (352.10 A)

Excitation of N v by electron impact

Inelastic electron impact cross sections are calculated for N V at energies between 1.0 and 16.0 Ryd in a close-coupling expansion over the 2s, 2p, 3s, 3p and 3d states of the ion. The close-coupling method is compared with the unitarized Coulomb-Born approximation and a distorted-wave calculation. Three additional pseudostates labelled 4s, 4p and 4d are included in the close-coupling expansion and are found to be unimportant. The authors attempt to establish the range of validity for the Coulomb-Born method at the given energies. In addition, results are compared with the values obtained by other investigators with particular emphasis on the 1s22s to 1s22p and 1s22s to 1s23p excitation cross sections which play an important role in determining temperatures of hot plasmas and the solar corona. The rate coefficients for 2s to nl transitions agree within experimental error with those of Boland et al. (1970) and Kunze and Johnston (1971).