THE SPECTRUM OF THE PLANETARY-NEBULA IC-418

A detailed high-spectral-resolution study of the spectrum of IC 418 is made for the region 3650 to 10050 angstrom, using the Hamilton echell e spectrograph of Lick Observatory, and of the UV spectral region with archival International Ultraviolet Explorer (IUE) data. From high-res olution images in both the near- and mid-infrared, Hora et al. (1993) showed that IC 418 probably has a compact shell interior to the detach ed, well-known, main shell emission. If one assumes a black body or Hu beny (or standard LTE) model atmosphere energy distribution, it does n ot appear possible to construct a fully satisfactory nebula model that will simultaneously represent the Hbeta flux, the [O III]5007/Hbeta r atio, and the scale of this planetary nebula (PN). Fortunately, IUE an d IR data supply information on ions in addition to those optically ob served so that the chemical composition can be reasonably well establi shed by summing over concentrations of observed ions. In spite of the fact that IC 418 is carbon rich in sense of having a C/O ratio exceedi ng the solar value, it is a ''metal-poor'' object. Possibly it resembl es IC 4997 but in a more advanced evolutionary phase. The central star is variable and has a strong wind.