Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...249..821p&link_type=abstract
Astrophysical Journal, Vol.249, P. 821, 1981
Astronomy and Astrophysics
Astrophysics
102
Scientific paper
Improved calculations are made for the line ratios R =f/i and G = (i+f)/r involving the forbidden (f), the intercombination (i), and the resonance (r) lines of helium-like ions: C V, O VII, Ne IX, Si XIII, Ca XIX, and Fe XXV. The ratios in ionization equilibrium are obtained over a range of electron temperatures. Departures from ionization equilibrium are also studied. in cases where the and the r lines appear blended together, the electron density may be derived from the observed ratio K=f/(i+r). We use the best available atomic data, including accurate rate coefficients for collisional excitation computed earlier, taking into account the effect of autoionizing resonances on electron impact cross sections. These effects enhance considerably the rates for the f and the transitions. For the line ratios observed in the Sun and in supernova remnants, the density and temperature diagnostics based on previous works may not be entirely correct.
Pradhan Anil Kumar
Shull Michael J.
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