The Excitation of Spectrum Lines in Nebulae by Resonant Scattering of Radiation from the Central Stars

Author:
  • MSM. J. Seaton
    M. J. Seaton
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Abstract
The spectra of planetary nebulae contain weak permitted lines of ions of oxygen, carbon and various other elements. It is shown that ion abundances, obtained on assuming these lines to be excited by recombination, are an order of magnitude too large. An alternative mechanism is therefore proposed: that excitation is by absorption of stellar radiation in spectrum lines. Approximate calculations show that this mechanism should be capable of explaining the observed line intensities. An improved estimate is obtained for the oxygen abundance in NGC 7027, N(O)/N(H) = 2.3 × 10 −4 .