Electron Collision and Transition Rates for S II and Fe XII

Details Electron Collision and Transition Rates for S II and Fe XII Electron Collision and Transition Rates for S II and Fe XII

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21641103t&link_type=abstract

American Astronomical Society, AAS Meeting #216, #411.03; Bulletin of the American Astronomical Society, Vol. 41, p.820

Astronomy and Astrophysics

Astrophysics

Scientific paper

Electron collisional excitation and transition rates of ions are important for computing electron temperatures and densities, ionization equilibria, and for deriving elemental abundances from emission lines formed in the collisional and photoionized plasmas. The electron density and line widths are important in constraining possible heating mechanisms. The bright Fe XII lines at 186.85, 186.89, 196.64, and 338.26 Å provide excellent density diagnostics for solar corona. The Fe XII lines at 196.64 and 186.89 Å are also density sensitive relative to any lines at 195.12, 193.51, and 192.39 Å. The collision strengths have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The close-coupling expansions include 70 levels of S II and 90 bound levels of Fe XII. An accurate representation of target levels has been obtained using spectroscopic and correlation non-orthogonal radial functions. The atomic wave functions give excitation energies which are in excellent agreement with experiment. Oscillator strengths and transition probabilities normally compare well with previous reliable calculations. The effective collision strengths have been calculated by integrating total resonant and non-resonant collision strengths over a Maxwellian distribution of electron energies over a wide temperature range suitable for modeling of astrophysical plasmas. Significant differences in collision strengths are noted with previous calculations.
This research work is supported by NASA under grant NNG09AB63G from the Planetary Atmospheres Program.

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