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Spatial Separation of the 3.29 Micron Emission Feature and Associated 2 Micron Continuum in NGC 7023

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Title: Spatial Separation of the 3.29 Micron Emission Feature and Associated 2 Micron Continuum in NGC 7023
Creators: An, Jin H.; Sellgren, K.
Keywords: dust, extinction
infrared: ISM
ISM: individual (NGC 7023)
ISM: lines and bands
ISM: molecules
reflection nebulae
Issue Date: 2003-12-10
Publisher: American Astronomical Society
Citation: Jin H. An and K. Sellgren, "Spatial Separation of the 3.29 Micron Emission Feature and Associated 2 Micron Continuum in NGC 7023," The Astrophysical Journal 599, no. 1 (2003), doi:10.1086/378630
DOI: 10.1086/378630
Abstract: We present a new 0".9 resolution 3.29 μm narrowband image of the reflection nebula NGC 7023. We find that the 3.29 μm infrared emission feature (IEF) in NGC 7023 is brightest in narrow filaments northwest of the illuminating star HD 200775. These filaments have been previously seen in images of extended red emission, K', near-infrared H_2 emission lines, the 6.2 and 11.3 μm IEFs, and HCO^+. We also detect 3.29 μm IEF emission faintly but distinctly between the filaments and the star. The 3.29 μm IEF image is in marked contrast to narrowband continuum images at 2.09, 2.14, and 2.18 μm, which show an extended emission peak midway between the filaments and the star, and much fainter emission near the filaments. The [2.18 μm]-[3.29 μm] color shows a wide variation, ranging from colors of 3.4-3.6 mag at the 2 μm continuum emission peak to a color of 5.5 mag in the 3.29 μm IEF emission filaments. A color of 5.5 mag is 1 mag higher than any published value in reflection nebulae. We observe [2.18 μm]-[3.29 μm] to increase smoothly with increasing projected distance from the illuminating star in NGC 7023, up until the brightest 3.29 μm IEF filament, suggesting that the main difference between the spatial distributions of the 2 μm continuum and the 3.29 μm IEF emission is related to the incident stellar flux. The 3.29 μm IEF is widely attributed to an aromatic C–H stretch, while the 2 μm continuum emission may be due to transient heating of tiny grains, fluorescence of aromatic molecules, or photoluminescence of larger grains. Our results suggest that the 3.29 μm IEF carriers are likely to be distinct from but related to the 2 μm continuum emitters. Our findings also imply that in NGC 7023 the 2 μm continuum emitters are mainly associated with H I, while the 3.29 μm IEF carriers are primarily found in warm H_2, but that both the 2 μm continuum emitters and the 3.29 μm IEF carriers can survive in H I or H_2.
ISSN: 1538-4357
URI: http://hdl.handle.net/1811/48188
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