Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-07-09
Astrophys.J. 615 (2004) 323-343
Astronomy and Astrophysics
Astrophysics
24 pages, 10 figures, accepted by ApJ. Preprint utilizes emulateapj.cls v. 4/12/04 (included)
Scientific paper
10.1086/424035
We present high signal-to-noise echelle spectra of the compact high surface brightness, low ionization planetary nebula IC 418. These reveal 807 emission lines down to intensities less than 10$^{-5}$ that of H$\beta$ for which we determine widths and relative intensities. We show that line profiles are a valuable parameter for making line identifications and in constraining the excitation mechanism of the lines. We present evidence that indicates that many supposed high-level recombination lines may in fact be excited by a process other than recombination. We contend from the detection of dielectronic recombination lines that their relatively low intensities argue against their making a significant contribution to level populations of the heavy ions in this object. Following similar analyses of other PNe we find that IC 418 shows a small discrepancy in ion abundances derived from forbidden vs. recombination lines of the heavy elements.
Baldwin Jack A.
Sharpee Brian
Williams Robert
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