2013A&A...554A..78P

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. 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. We searched for acetone within our IRAM Plateau de Bure Interferometer 3mm and 1.3mm data sets. Twenty-two acetone lines were searched within these data sets. The angular resolution ranged from 1.8"x0.8" to 6.0"x2.3", and the spectral resolution ranged from 0.4 to 1.9km/s. 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 150K is determined toward Ace-1 and Ace-2, and the acetone column density is estimated to be 2-4x10¹⁶cm^–2 with a relative abundance of 1-6x10^–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.