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- J. Cernicharo, A. M. Heras, J. R. Pardo,
.G.G.M. Tielens,
M. Guelin, E. Dartois, R. Neri, and L.B.F.M. Waters
"Methyl-polyynes and Small Hydrocarbons in CRL 618"
Astrophysical Journal Letters, 546, 2/2, L123-L126 (2001).
We report on the detection with the Infrared Space Observatory (ISO) of
strong infrared absorption from NH3 and C2H4 in CRL618.
The observed NH3 and C2H4 bands arise from a region with kinetic
temperatures ~ 200 K, i.e., the dense gas in the PDR associated to
the dense torus surrounding the central star as was the case for the
polyynes and cyanopolyynes (see previous Letter).
Several absorption bands, probably arising from
small gas phase hydrocarbons, are observed between 5.5 and 11 microns.
Two of these species have been identified with the 30-m IRAM telescope
as the methyl-polyynes CH3C2H and CH3C4H.
However, the absorption around 6.2 microns is particularly broad and could
arise from the combination of these small hydrocarbons and from the
aromatic C=C stretching of PAHs of moderate size. These bands and those
associated to the polyynes, cyanopolyynes, methylpolyynes and to
benzene are not present in the infrared spectrum of the AGB star IRC+10216
(see Cernicharo et al. 1999).
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