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B. Sharpee (SRI International), J.A. Baldwin (Michigan State University), R.E. Williams (Space Telescope Science Institute)
Presented here are high-resolution spectra of the low-ionization planetary nebula IC 418. These spectra reveal 600+ emission lines which we have identified with the automated software package EMILI, including numerous recombination lines, many never before observed in IC 418, from various CNONe ions. Using the latest effective recombination coefficients, abundances have been determined from the strengths of these recombination lines and compared to those determined from the collisionally excited lines of the same source ion. The recombination line abundances consistently exceed those from collisionally excited lines, as has been shown in numerous other planetary nebulae and H II regions, by a varying amount ranging from near agreement for O+2, to near an order of magnitude for Ne+2. The relatively simple expansion geometry of IC 418 yields line profiles that localize the origin of these lines' parent species. These profiles clearly show that there is a significant contribution to the strengths of recombination lines of low ionization species (O+ and N+) from ground state fluorescence processes, and that the O II and N II permitted lines originate from O+2 and N+2.
The author(s) of this abstract have provided an email address for comments about the abstract: brian.sharpee@sri.com
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.