[en] An extensive review of Born approximation calculations is given for excitation by electron and proton impact, ionization by electron and proton impact, and excitation and ionization by atomic impact. The results are compared with available experimental data. (36 figures, 219 references) (U.S.)

[en] Theoretical calculations for the electron impact excitation of the ions Si II, Si III, Si IV, S II, S III, and S IV are reviewed. For each ion, the accuracy and validity of the different calculations are discussed and recommended effective collision strengths are presented. 33 refs., 9 figs., 7 tabs

[en] The extreme ultraviolet emission-line spectrum of very intense sunspot plumes is analyzed. Several of the standard density diagnostics suggest a constant density, rather than constant pressure, emitting region. Temperature diagnostic line ratios of several ions yield temperatures below those expected in ionization equilibrium (and observed in the quiet Sun). This provides strong evidence for the suggestion that the internal energy of cooling, falling gas accounts for the observed radiation. The lack of such departures from equilibrium in the quiet Sun demonstrates that downflows are not the dominant source of energy at transition region temperatures. We assess the accuracy of several atomic rate coefficients

No abstract available

[en] Electron-impact excitation rates for transitions in S IV, Al III, and N IV, determined with the R-matrix code, are used to calculate relative level populations for electron temperatures log Te = 4.4 - 5.4 and densities Ne between 10 to the 8th and 10 to the 12th/cu cm. These data are combined with similar results for C III and O III to derive emission-line ratios which should be useful as electron-density diagnostics when applied to the UV spectra of late-type stellar atmospheres. 37 refs

[en] The Λ and |chi| coincidence parameters for the 1¹S-2¹P electron excitation of helium are calculated using results from an eleven-state R-matrix calculation. It is shown that in the region of resonances the parameters vary rapidly. However the rapid variation only occurs over an energy range approximately equal to the width of the resonance. (author)

No abstract available

[en] This is the latest in a sequence of R-matrix calculations on electron-helium scattering in which target states with successively higher principal quantum number are explicitly included in the close-coupling expansion. A 19-state n(≤4) calculation is presented. Such calculations yield accurate excitation cross sections in the collision energy range up to the highest threshold explicitly included. Collisional excitation rates are calculated which show the extent to which the rates to the n = 3 levels were overestimated in a previous 11-state calculation. In particular, the collision rates given here for the astrophysically important 2³S-3³D and 2³S-3¹D transitions are respectively 40 and 30% lower than the 11-state rates used by a previous worker in the calculation on the primordial helium abundance. (author)

No abstract available

[en] The distorted-wave second Born approximation has been applied to the elastic scattering of electrons by ground-state atomic hydrogen and to the electron impact excitation of the 1s → 2s and 1s → 2p transitions in the energy range 30 to 680 eV. Differential and total cross sections are given as well as the polarisation fraction of the Lyman α radiation resulting from the radiative transition 2p → 1s. The results obtained are compared with both theoretical and experimental data of previous workers. (U.K.)