2006/09/28 by Gordon M. MacAlpine, G. M. MacAlpine, Tait C. Ecklund +7 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/509504
published as Astron.J.133:81-88,2007 · 14 pages, 12 figures, to be published in the Astronomical Journal
arxiv created 2006/09/28 · openalex publication_date 2006/11/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We present and discuss correlations for optical and near-infrared (5500-10030 Å) line intensity measurements at many positions in the Crab Nebula. These correlations suggest the existence of gas produced by a range of nuclear processing, from material in which synthesis ended with the CNO cycle, to some helium burning and nitrogen depletion, to regions containing enriched products of oxygen burning. The latter exhibit a gradual, linear rise of [Ni II] emission with increasing argon enrichment, whereas gas with less nuclear processing shows markedly different [Ni II] emission characteristics, including the highest derived abundances. This suggests two origins for stable, neutron-rich nickel in the nebula: a type of "alpha-rich freeze out" in the more highly processed material and possibly removal of ions from the neutron star in other regions. In addition, the data indicate that anomalously strong observed [C I] emission comes from broad, low-ionization H + to H 0 transition zones. Although the strongest He I emission could also be enhanced in similar low-ionization gas, correlations between relevant line ratios argue against that interpretation, strengthening the case for an exceptionally high helium mass fraction in some locations.