Mid-infrared imaging of WL 16: the spatial distribution of the hydrocarbon emission features |
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| Authors: | Moore Emerson Skinner Meixner Arens & Jernigan |
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| Institution: | Astrophysics Research Institute, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF,;Department of Physics, Queen Mary and Westfield College, Mile End Road, London E1 4NS,;Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA,;Department of Astronomy, MC 221, University of Illinois, Urbana-Champaign, IL 61801, USA,;Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA |
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| Abstract: | We present arcsec-resolution images at 8.2, 10.0 and 11.3 μm of the unusual young object WL 16 in Ophiuchus, which has an extended envelope of fluorescing hydrocarbon molecules. To the limit of achieved sensitivity, the faint 10.0-μm continuum has a surface-brightness distribution that is not distinguishable from those at 8.2 and 11.3 μm, where the luminosity is known to be dominated by the polycyclic aromatic hydrocarbon (PAH) emission features. We conclude that the 10-μm continuum either arises from non-equilibrium heating of small dust grains that are well mixed with the hydrocarbons or is quasi-continuous emission from the PAH particles themselves, rather than thermal equilibrium emission from macroscopic dust grains, and that there is no significant silicate absorption variation across the source. The extended hydrocarbon emission may trace a flattened, equatorial distribution of circumstellar material or arise in bipolar lobes. The former case is slightly favoured, based on currently available data, and would imply that WL 16 is a relatively evolved Herbig Ae star, the equatorial plane of which has been almost cleared of normal dust, leaving only fluorescing hydrocarbons and larger coagulated particles as a possibly transient fossil of the original circumstellar disc. |
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| Keywords: | circumstellar matter stars: pre-main-sequence dust extinction ISM: individual: WL 16 ISM: molecules infrared: ISM: lines and bands |
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