Journal Article

Excitation of emission lines by fluorescence and recombination in IC 418

V. Escalante, C. Morisset and L. Georgiev

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 426, issue 3, pages 2318-2334
Published in print November 2012 | ISSN: 0035-8711
Published online November 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21862.x
Excitation of emission lines by fluorescence and recombination in IC 418

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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.

Keywords: atomic processes; planetary nebulae: individual: IC 418

Journal Article.  11495 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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