2006/07/24 by Joseph L. Hora, William B. Latter, Howard A. Smith +3 · 6 citations
Chemistry · Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Emission nebula #Emission spectrum #Excited state #Geometry #Infrared #Line (geometry) #Nebula #Photochemistry #Photodissociation #Physics #Planetary nebula #Spectral line #Spitzer Space Telescope #Stars #Stellar, planetary, and galactic studies #Telescope #astro-ph
paper · pdf · doi:10.1086/507944
published as Astrophys.J.652:426-441,2006; Erratum-ibid.656:629,2007 · 24 pages, 19 figures, accepted for publication in the Astrophysical Journal. A version of the paper with higher resolution images is available at http://cfa-www.harvard.edu/irac/publications/2006refereed/jhora_helix.pdf
arxiv created 2006/07/24 · openalex publication_date 2006/11/16 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have mapped the Helix (NGC 7293) planetary nebula (PN) with the IRAC instrument on the Spitzer Space Telescope . The Helix is one of the closest bright PNs and therefore provides an opportunity to resolve the small-scale structure in the nebula. The emission from this PN in the 5.8 and 8 μm IRAC bands is dominated by the pure rotational lines of molecular hydrogen, with a smaller contribution from forbidden line emission such as [Ar III] in the ionized region. The IRAC images resolve the "cometary knots," which have been previously studied in this PN. The "tails" of the knots and the radial rays extending into the outer regions of the PN are seen in emission in the IRAC bands. IRS spectra on the main ring and the emission in the IRAC bands are consistent with shock-excited H 2 models, with a small (~10%) component from photodissociation regions. In the northeast arc, the H 2 emission is located in a shell outside the Hα emission.