THE RATIO OF OPTICAL-TO-INFRARED EMISSION-LINE STRENGTHS IN AR(III) AS ELECTRON-DENSITY DIAGNOSTICS FOR PLANETARY-NEBULAE

Electron impact excitation rates for transitions in Ar III, calculated with the R-matrix code, are used to derive the electron density sensi tive emission line ratio R1 = I(3s(2)3p4 P-3(2)-3s(2)3p4 1D)/I(3s(2)3p 4 P-3(2)-3s(2)3p4 P-1(3)) = 1(7135 angstrom)/I(9 mum) for a range of e lectron temperatures (T(e) = 5000-30,000 K) and densities (N(e) = 10(2 )-10(6) cm-3) applicable to planetary nebulae. Electron densities dedu ced from the observed values of R1 in several planetaries, measured us ing ground-based instrumentation, are in good agreement with those der ived from N(e)-sensitive line ratios in other species, which provides observational support for the accuracy of the atomic data adopted in t he calculations. The potential usefulness of the Ar III emission line ratio R2 = I(3s(2)3p4 P-3(1)-3s(2)3p4 P-3(0))/I(3s(2)3p4 P-3(2)-3s(2)3 p4 P-3(1)) = I(21.8-mum)/I(9 mum) as an N(e)-diagnostic is briefly dis cussed.