Metal Absorption Profiles from the Central Star of the Planetary Nebula M27 (NGC 6853, PN G060.8−03.6, the Dumbbell): Photospheric and Nebular Line Identifications

Abstract

High resolution spectra of the hot central star of the planetary nebula (CSPN) M27, acquired with the Far Ultraviolet Spectroscopic Explorer (\FUSE), have revealed an unusually rich set of narrow molecular hydrogen absorption features. This object is also unique in that the velocity of nebular absorption features are cleanly separated from the velocity of the intervening interstellar medium. These features blend with and in many cases obscure atomic features. We have developed a continuum model of the CSPN including atomic and molecular hydrogen absorption. Using this model we have identified and tabulated the metal lines as arising from either photospheric, nebular and/or non-nebular velocity systems. We find the nebular outflow and ionization balance to be stratified with high ionization states favored at low velocity and low ionization states favored at high velocity. Neutrals and molecules are found at a velocity that marks the transistion between these two regimes. These observations are a challenge to the interacting wind model of PN evolution. Mappings at high resolution of the line profiles for \ion{C}{1} \ion{-}{4}, \ion{N}{1} \ion{-}{3}, \ion{O}{1}, \ion{O}{6}, \ion{Si}{2} \ion{-}{4}, \ion{P}{2} \ion{-}{5}, \ion{S}{2} \ion{-}{4}, \ion{Ar}{1} \ion{-}{2} and \ion{Fe}{2} \ion{-}{3} within the \FUSE and STIS bandpasses are presented. The digitial spectra of the stars and the model are freely available on the H$_2$ools website. They will be useful for photospheric analyses seeking to determine the metallicity of the central star and for absorption line based atomic and molecular abundance determination of the nebular outflow.