The Helix Nebula is a low-density, stratified object with near-solar oxygen abundance (8.7), a ~1 dex sulfur deficit, and moderate helium/nitrogen enrichment placing it near the Type I boundary, with abundance variations attributed to ionization structure rather than chemical inhomogeneity.
HST and FUSE Spectroscopy of Hot Hydrogen-Rich Central Stars of Planetary Nebulae
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abstract
High-resolution UV spectra, obtained with HST and FUSE, enable us to analyse hot hydrogen-rich central stars in detail. Up to now, optical hydrogen and helium lines have been used to derive temperature and surface gravity. Those lines, however, are rather insensitive; in particular, neutral helium lines have completely vanished in the hottest central stars. Therefore, we have concentrated on ionization balances of metals, which have a rich line spectrum in the UV, to establish a new temperature scale for our sample. Furthermore, we have determined abundances of light metals, which had been poorly known before. They show considerable variation from star to star. We present results of quantitative spectral analyses performed with non-LTE model atmospheres.
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SDSS-V LVM: Revealing the Physical and Chemical Structure of the Helix Nebula
The Helix Nebula is a low-density, stratified object with near-solar oxygen abundance (8.7), a ~1 dex sulfur deficit, and moderate helium/nitrogen enrichment placing it near the Type I boundary, with abundance variations attributed to ionization structure rather than chemical inhomogeneity.