Physical Processes in Gaseous Nebulae. XVII. Fluorescence in High-Excitation Planetaries.

Some years ago Bowen attributed the appearance of "fractional multiplets" of 0 iii in the spectra of high-excitation planetaries to absorption by 0 m atoms in the 2p2 3~2 level of the X 303.80 "Lyman alpha" radiation of helium. The subsequent cascading of these atoms from 2p3d 3D2 of 0 m back to the ground level via the 2p3p and 2~3S configurations are supposed to produce the observed lines. We have attempted to put this theory on a quantitative basis by setting up the appropriate equations of sta- tistical equilibrium for the excited levels and predicting the relative intensities of the observed ultraviolet lines. A comparison of observed relative intensities with predicted relative intensities yields a con- sistency check on the theory. The populations of the excited levels are found to be 10 4~IoI6 atoms cm3. The intensity of the radiation in the 0 m 303.80 line is from ~ to ~ times greater than that radiated by the nuclear star, which illustrates why permitted lines of 0 rn other than those originating by cascade from 3d~P2, are not observed. The excess is attributed to the concentration of radiation in these lines, by cyclic processes resulting from ionization of He+. We have also shown that theoretically the images of the Bowen lines shoiild be about 5 per cent larger than those of the He ii lines, which is in rough agreement with the observational data. The paper contains tables of the relevant f's and A's computed from approximate wave functions based on Slater's rules