FORBIDDEN LINES OF [O I] IN THE HIGH-RESOLUTION OPTICAL SPECTRA OF PLANETARY NEBULAE

Abstract

ABSTRACT Electron impact excitation rates for transitions in O I, calculated with the R-matrix code, are used to derive the electron temperature sensitive emission line ratio R = I(2s2p4 1D - 2s2 2p4 1S)/I(2s2 2p4 3P1,2 - 2x2 2p4 1D) = I(5577 A)/I(6300 + 6365 A), for a range of electron temperatures (Te = 5000 - 20000 K) and d 2ensities (ne = 104 - 106 cm-3) applicable to planetary nebulae. Experimental values of R for a number of planetaries have been measured from high resolution (~0.6 A FWHM) spectra obtained with the Hamilton Echelle spectrograph on the 3 m telescope at the Lick Observatory. These measurements should be particularly reliable, as the sample of planetaries was restricted to those with large enough radial velocities for the nebular [O I] 5577 A emission to be red- or blue-shifted from the atmospheric airglow feature by a sufficient amount for the former to be reliably determined. Electron temperatures deduced from the observed values of R are generally in good agreement with those derived from Te sensitive line ratios in other species, providing observational support for the accuracy of the atomic data adopted in the calculations.