Acetone in Orion BN/KL - High-resolution maps of a special
  oxygen-bearing molecule
  As one of the prime targets of interstellar chemistry study, Orion BN/KL
clearly shows different molecular distributions between large nitrogen- (e.g.,
C2H5CN) and oxygen-bearing (e.g., HCOOCH3) molecules. However, acetone
(CH3)2CO, a special complex O-bearing molecule, has been shown to have a very
different distribution from other typical O-bearing molecules in the BN/KL
region. We searched for acetone within our IRAM Plateau de Bure Interferometer
3 mm and 1.3 mm data sets. Twenty-two acetone lines were searched within these
data sets. The angular resolution ranged from 1.8 X 0.8 to 6.0 X 2.3 arcsec^2,
and the spectral resolution ranged from 0.4 to 1.9 km s-1. Nine of the acetone
lines appear free of contamination. Three main acetone peaks (Ace-1, 2, and 3)
are identified in Orion BN/KL. The new acetone source Ace-3 and the extended
emission in the north of the hot core region have been found for the first
time. An excitation temperature of about 150 K is determined toward Ace-1 and
Ace-2, and the acetone column density is estimated to be 2-4 X 10^16 cm-2 with
a relative abundance of 1-6 X 10^-8 toward these two peaks. Acetone is a few
times less abundant toward the hot core and Ace-3 compared with Ace-1 and
Ace-2.
  We find that the overall distribution of acetone in BN/KL is similar to that
of N-bearing molecules, e.g., NH3 and C2H5CN, and very different from those of
large O-bearing molecules, e.g., HCOOCH3 and (CH3)2O. Our findings show the
acetone distribution is more extended than in previous studies and does not
originate only in those areas where both N-bearing and O-bearing species are
present. Moreover, because the N-bearing molecules may be associated with
shocked gas in Orion BN/KL, this suggests that the formation and/or destruction
of acetone may involve ammonia or large N-bearing molecules in a shocked-gas
environment.
