Infrared Observations of The Helix Planetary Nebula

Abstract

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 PN, 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 micron 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 H2 models, with a small (~10%) component from photodissociation regions. In the Northeast Arc, the H2 emission is located in a shell outside of the H alpha emission.

arXiv comment24 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

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• Spitzer mid-infrared spectroscopic observations of planetary nebulae
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• Discovery of Multiple Shells Around the Planetary Nebula IC 418
• Planck intermediate results. XVIII The millimetre and sub-millimetre emission from planetary nebulae
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• Herschel imaging of the dust in the Helix Nebula (NGC 7293)
• Sampling Molecular Gas in the Helix Planetary Nebula: Variation in HNC/HCN with UV Flux
• Comparing shocks in planetary nebulae with the solar wind termination shock
• Modelling the Warm H2 Infrared Emission of the Helix Nebula Cometary Knots
• Introducing PyCross: PyCloudy Rendering Of Shape Software for pseudo 3D ionisation modelling of nebulae
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• JWST observations of the Ring Nebula (NGC 6720) -- II. PAH emission
• Spitzer Observations of Planetary Nebulae
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