Hidden IR structures in NGC 40: signpost of an ancient born-again event

Abstract

We present the analysis of infrared (IR) observations of the planetary nebula NGC 40 together with spectral analysis of its [WC]-type central star HD 826. Spitzer IRS observations were used to produce spectral maps centred at polycyclic aromatic hydrocarbons (PAH) bands and ionic transitions to compare their spatial distribution. The ionic lines show a clumpy distribution of material around the main cavity of NGC 40, with the emission from [Ar II] being the most extended, whilst the PAHs show a rather smooth spatial distribution. Analysis of ratio maps shows the presence of a toroidal structure mainly seen in PAH emission, but also detected in a Herschel PACS 70 mic image. We argue that the toroidal structure absorbs the UV flux from HD 826, preventing the nebula to exhibit lines of high-excitation levels as suggested by previous authors. We discuss the origin of this structure and the results from the spectral analysis of HD 826 under the scenario of a late thermal pulse.

10 pages, 10 figures; Accepted to MNRAS

References in corpus (10)

• Spectral Mapping Reconstruction of Extended Sources
• Carbon-rich dust past the asymptotic giant branch: aliphatics, aromatics, and fullerenes in the Magellanic Clouds
• Detailed Far-UV to Optical Analysis of Four [WR] Stars
• PAH Formation in O-rich Planetary Nebulae
• The Spitzer IRS view of V4334 Sgr (Sakurai's Object)
• Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78
• The born-again planetary nebula A78: an X-ray twin of A30
• The Halo and Rings of the Planetary Nebula NGC 40 in the Mid-Infrared
• On the robustness of H-deficient post-AGB tracks
• Planetary Nebulae with Ultra-Violet Imaging Telescope (UVIT): Far Ultra-violet halo around the Bow Tie nebula (NGC 40)

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• A carbon-rich hot bubble in the planetary nebula NGC 5189
• Spectroscopic survey of faint planetary-nebula nuclei III. A [WC] central star and two new PG1159 nuclei
• Planetary nebulae with Wolf-Rayet-type central stars -- IV. NGC 1501 and its mixing layer
• A primer on the formation and evolution of hydrogen deficient Central Stars of Planetary Nebulæ and Related Objects
• Adjusting the bow-tie: A morpho-kinematic study of NGC40
• Hot bubbles of planetary nebulae with hydrogen-deficient winds. III. Formation and evolution in comparison with hydrogen-rich bubbles
• Evidence for cold plasma in planetary nebulae from radio observations with the LOw Frequency ARray (LOFAR)