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Spatial variations of the 3 micron emission features within UV-excited nebulae - Photochemical evolution of interstellar polycyclic aromatic hydrocarbonsSpectra at 3 microns have been obtained at several positions in the Orion Bar region and in the nebula surrounding HD 44179. Weak emission features at 3.40, 3.46, 3.51, and 3.57 microns are prominent in the Orion Bar region. The 3.40- and 3.51-micron features increase in intensity relative to the dominant 3.29-micron feature. The spectrum obtained in the Red Rectangle region 5 arcsecs north of HD 44179 are similar to those in the Orion Bar, with a weak, broad 3.40-micron feature at the position of HD 44179. The spatial behavior of the weak emission features is explained in terms of hot bands of the CH stretch and overtones, and combination bands of other fundamental vibrations in simple PAHs. Based on the susceptibility of PAHs to destruction by the far UV fields in both regions, PAH sizes are estimated at 20-50 carbon atoms.
Document ID
19890054004
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Geballe, T. R.
(Joint Astronomy Center Hilo, HI; ASTRON, Amsterdam, Netherlands)
Tielens, A. G. G. M.
(NASA Ames Research Center Moffett Field, CA; California, University, Berkeley, United States)
Allamandola, L. J.
(NASA Ames Research Center Moffett Field, CA, United States)
Moorhouse, A.
(Hawaii Univ. Hilo, HI, United States)
Brand, P. W. J. L.
(Royal Observatory Edinburgh, United Kingdom)
Date Acquired
August 14, 2013
Publication Date
June 1, 1989
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 341
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
89A41375
Distribution Limits
Public
Copyright
Other

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