Identification and Characterization of Faint Emission Lines in the Spectrum of the Planetary Nebula IC 418
Abstract
We present high signal-to-noise ratio echelle spectra of the compact high surface brightness, low-ionization planetary nebula (PN) IC 418. These reveal 807 emission lines down to intensities less than 10-5 that of Hβ 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 versus recombination lines of the heavy elements.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2004
- DOI:
- 10.1086/424035
- arXiv:
- arXiv:astro-ph/0407186
- Bibcode:
- 2004ApJ...615..323S
- Keywords:
-
- ISM: Abundances;
- Line: Formation;
- Line: Profiles;
- ISM: Planetary Nebulae: Individual: Alphanumeric: IC 418;
- Astrophysics
- E-Print:
- 24 pages, 10 figures, accepted by ApJ. Preprint utilizes emulateapj.cls v. 4/12/04 (included)