| Abstract
| - Aims. As one of the prime targets of interstellar chemistry study, Orion BN/KL clearly shows different molecular distributions between large nitrogen- (e.g., C 2H 5CN) and oxygen-bearing (e.g., HCOOCH 3) molecules. However, acetone (CH 3) 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. Therefore, it is worth investigating acetone in detail at high angular resolutions, which will help us understand the formation of this molecule and its chemical role in the complex BN/KL region. Methods. 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 \hbox{$1\farcs8\times0\farcs8$}1.″8×0.″8 to \hbox{$6\farcs0\times2\farcs3$}6.″0×2.″3, and the spectral resolution ranged from 0.4 to 1.9 km s -1. Results. 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 × 10 16 cm -2 with a relative abundance of 1−6 × 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. Conclusions. We find that the overall distribution of acetone in BN/KL is similar to that of N-bearing molecules, e.g., NH 3 and C 2H 5CN, and very different from those of large O-bearing molecules, e.g., HCOOCH 3 and (CH 3) 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.
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