Excitation of emission lines by fluorescence and recombination in IC 418

Escalante, V.; Morisset, C.; Georgiev, L.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 426, Issue 3, pp. 2318-2334.

Advertised on:
11
2012
Number of authors
3
IAC number of authors
1
Citations
22
Refereed citations
19
Description
We compare calculated intensities of lines of C II, N I, N II, O I and O II with a published deep spectroscopic survey of IC 418. Our calculations use a self-consistent nebular model and a synthetic spectrum of the central star atmosphere to take into account line excitation by continuum fluorescence and electron recombination. We found that the N II spectrum of the s, p and most d states is excited by fluorescence due to the low-excitation conditions of the nebula. Many C II and O II lines have significant amount of excitation by fluorescence. Recombination excites all the lines from the f and g states and most O II lines. In the neutral-ionized boundary, the N I quartet and O I triplet dipole-allowed lines are excited by fluorescence, while the quintet O I lines are excited by recombination. Electron excitation produces the forbidden optical lines of O I, and continuum fluorescence enhances the N I forbidden line intensities. Lines excited by fluorescence of light below the Lyman limit thus suggest a new diagnostic to explore the inner boundary of the photodissociation region of the nebula.
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