Effective collision strengths for astrophysically important quartet-quartet ultraviolet transitions in S II

Effective collision strengths for electron-impact excitation of S II from the ground 3p3 4So state to the higher lying 3p4 4Pe, 4s 4Pe, 3d 4Fe, 3d 4De and 3d 4Pe excited states are presented over a wide range of temperatures of astrophysical interest (Log (Te) = 3.5–5.1 K). The collision strengths are calculated in the close-coupling approximation using the R-matrix method and sophisticated configuration-interaction wavefunctions are used to represent the 18 target state which are included in the calculation. Convergence behaviors are examined by comparing the present 18-state work with earlier 12-state, 6-state, 5-state and 2-state calculations. Significant deviations are, however, found to occur for all five optical transitions considered, and in particular the present results indicate that the effective collision strengths in low impact energies are greatly enhanced by the presence of resonances converging to the higher lying thresholds. The accurate effective collision strengths are fitted to interpolation formulae which are valid for the range of temperatures 3200 to 100 000 degrees Kelvin. Interpolated values may readily be obtained using a Numerical Algorithm Group (NAG) library routine or by an easily coded algorithm.

[1]  C. Ramsbottom,et al.  Electron Impact Excitation Rates for Transitions Involving the n = 2 and n = 3 Levels of Beryllium-like Ne VII , 1995 .

[2]  K A Berrington,et al.  Electron impact excitation rates for transitions involving the n = 2 and n = 3 levels of beryllium-like N IV , 1994 .

[3]  Anil K. Pradhan,et al.  Excitation rate coefficients and line ratios for the optical and ultraviolet transitions in S II , 1993 .

[4]  H. Ferguson,et al.  Determination of ionic abundances in the Io torus using the Hopkins Ultraviolet Telescope , 1991 .

[5]  Y. K. Ho,et al.  Collision strengths for dipole-allowed transitions in S II , 1990 .

[6]  A. Hibbert,et al.  Oscillator strengths for transitions among the low-lying energy levels of S II , 1989 .

[7]  J. Lieske,et al.  Detection of neutral oxygen and sulfur emissions near Io using IUE , 1987 .

[8]  S. Tayal,et al.  Effective collision strengths for electron impact excitations in S II. [Plasma torus of Io] , 1987 .

[9]  D. Shemansky,et al.  The Voyager 1 EUV spectrum of the Io plasma torus , 1981 .

[10]  D. Strobel,et al.  Overview of the Voyager ultraviolet spectrometry results through Jupiter encounter , 1981 .

[11]  D. Strobel,et al.  Properties of the Io plasma torus inferred from Voyager EUV data , 1980 .

[12]  D. Shemansky.  Radiative cooling efficiencies and predicted spectra of species of the IO plasma torus , 1980 .

[13]  J. Blamont,et al.  Extreme Ultraviolet Observations from Voyager 1 Encounter with Jupiter , 1979, Science.

[14]  P. Feldman,et al.  Hopkins Ultraviolet Telescope Determination of the Io Torus Electron Temperature , 1994 .