Open AccessMid‐infrared imaging of WL 16: the spatial distribution of the hydrocarbon emission features
Author(s) -
T. J. T. Moore,
J. P. Emerson,
C. J. Skinner,
M. Meixner,
J. F. Arens
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01883.x
Subject(s) - physics , astrophysics , hydrocarbon , brightness , infrared , circumstellar dust , polycyclic aromatic hydrocarbon , circumstellar envelope , cosmic dust , astronomy , astrobiology , chemistry , stars , organic chemistry
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.