Emission lines of OIII in the optical and ultraviolet spectra of planetarynebulae

Recent R-matrix calculations of electron impact excitation rates in O III a re used to calculate electron temperature and density-dependent emission li ne ratios R-1 = I(4363 Angstrom)/I(4960 Angstrom + 5007 Angstrom), R-2 = I(1661 Angstrom + 1667 Angstrom /I(4960 Angstrom + 5007 Angstrom) and R-3 = I(2322 Angstrom)/I(1661 Angstrom + 1667 Angstrom), for a range of electron temperatures (7500 less than or equal to T-e less t han or equal to 30 000 K) and densities(10(4) less than or equal to N-e les s than or equal to 10(7) cm(-3)) applicable to gaseous nebulae. The ratio-r atio diagrams(R-1, R-2) and (R-1, R-3) should, in principle, allow the simu ltaneous determination of T-e and N-e from measurements of the O III featur es in a spectrum. Plasma parameters derived for a sample of mid- to high-ex citation planetary nebulae from (R-1, R-2) and (R-1, R-3) measurements, pro duced using a combination of ultraviolet spectra obtained with the internat ional Ultraviolet Explorer (IUE) and optical data from a number of observin g runs, are found to show excellent internal consistency. They also show, i n general, good agreement with the values of T-e and N-e estimated from oth er line ratios in the nebulae, therefore providing observational support fo r the accuracy of the theoretical ratios and hence the atomic data adopted in their derivation.