1994PASP..106..745H

A detailed high spectral resolution study of the spectrum of IC 418 is made for the region 3650A to 10050A, using the Hamilton echelle spectrograph of Lick Observatory, and of the UV spectral region with archival International Ultraviolet Explorer (IUE) data.

From the high resolution images in both the near- and mid-infrared, Hora et al. (1993) showed that IC 418 probably has a compact shell interior to the detached, well-known, main shell emission. If one assumes a black body or Hubeny (or standard LTE) model atmosphere energy distribution, it does not appear possible to construct a fully satsifactory nebula model that will simultaneously represent the H-beta flux, hte [O III] 5007/H-beta ratio, and the scale of this planetary nebula (PN). Fortunately, IUE and IR data supply information on ions in addition to those optically observed so that the chemical composition can be reasonably well-established by summing over concentrations of observed ions. In spite of fact that IC 418 is carbon rich in sense of having a C/O ratio exceeding the solar value, it is a "metal-poor" object. Possibly it resembles IC 4997 but in a more advanced evolutionary phase. The central star is variable and has a strong wind.