HCOOCH_3 as a probe of temperature and structure of Orion-KL
Abstract
The Orion Kleinmann-Low nebula is the closest (~414 pc) and the most studied massive star formation region. Several components (Hot Core, Plateau, Compact Ridge and Extended Ridge) are associated with Orion-KL. These have different chemical and physical properties: distinct spectral signatures and kinetic temperatures, different spatial distributions in complex molecules. Whereas its proximity allows studies on a scale of a few hundred AU (or down to <50 AU in molecular H2 emission), spectral confusion makes it difficult to identify molecules with low abundances. We used high spectral and spatial resolution millimetre observations (from 7" to 2" and from 2.3 km/s to 0.4 km/s, respectively) from the Plateau de Bure Interferometer in order to reduce the spectral confusion. Using the high angular resolution of 1.8"x0.8" we have focused our study on an important oxygenated molecule, methyl formate HCOOCH3, to characterize the physical conditions, temperature and density of the various molecular components. We identify 28 methyl formate emission peaks of which the two stongest ones are in the Compact Ridge and in the South West of the Hot Core. Our observations show that 1) the Compact Ridge region seems to be heated by external mechanisms (e.g. shocks), 2) the LSR velocity of the gas is between 7.5 and 8.0 km/s depending on the positions, 3) a second velocity component at 9-10 km/s is identified along a North-South structure including the Compact Ridge and the BN object, 4) a very clear association is found between our methyl formate maps and the 2.12 μm excited H2 maps. This tends to confirm a scenario of HCOOCH3 production involving the release of molecules from ice mantles, either methyl formate itself or a precursor, for example CH3OH.
- Publication:
-
The Molecular Universe
- Pub Date:
- May 2011
- DOI:
- 10.48550/arXiv.1103.2548
- arXiv:
- arXiv:1103.2548
- Bibcode:
- 2011IAUS..280P.156F
- Keywords:
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- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in A&