High-resolution maps of a special oxygen-bearing molecule
1 Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France
2 CNRS, LAB, UMR 5804, 33270 Floirac, France
3 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
4 Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109, USA
5 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
6 Naval Research Laboratory, Code 7213, Washington, DC 20375, USA
7 Observatoire de Paris, LERMA, CNRS, 61 Av. de l’Observatoire, 75014 Paris, France
8 Laboratoire de Physique des Lasers, Atomes et Molécules, Université de Lille 1, UMR 8523, 59655 Villeneuve d’Ascq Cedex, France
Received: 12 December 2012
Accepted: 30 March 2013
Aims. 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.
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 to , 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 × 1016 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., 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.
Key words: ISM: clouds / ISM: molecules / astrochemistry / submillimeter: ISM
Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).
Appendices and movie are available in electronic form at http://www.aanda.org
© ESO, 2013