HCOOCH3 as a probe of temperature and structure in Orion-KL

摘要: Context. The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on scale few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. Aims: We studied an important oxygenated molecule, HCOOCH3, characterize the physical conditions, temperature, and density different molecular source components. Methyl formate presents strong close rotational transitions covering wide range energy, emission in Orion-KL not contaminated by N-bearing molecules. This study will help future 1) constrain chemical models for formation methyl gas phase or grain mantles 2) search more prebiotic Methods: used high-resolution observations from IRAM Plateau de Bure Interferometer reduce better isolate regions. twelve data sets spatial resolution down 1.8″ × 0.8″. Continuum was subtracted selecting apparently line-free channels. Results: 28 peaks throughout 50″ field observations. two strongest peaks, named MF1 MF2, are Compact Ridge southwest Hot Core, respectively. From comparison single-dish observations, we estimate that miss less than 15% flux still prevailing as half expected blended over region. Assuming thermalized, derive temperature at five main peaks. At position find 80 K 0.8″ beam size 120 larger (3.6″ 2.2″), suggesting external heating, whereas about 130 MF2 both scales. Transitions first torsionally excited state detected well, good agreement positions diagrams between ground vt = 1 suggests similar temperature. LSR velocity 7.5 8.0 km s-1 depending column vary 1.6 1016 1017 cm-2. A second component observed around 9-10 north-south structure stretching up BN object, this warmer peak. other C2H4O2 isomers detected, derived upper limit ≤3 1014 cm-2 glycolaldehyde ≤2 1015 acetic acid. 223 GHz continuum map, several dust clumps associated masses 0.8 5.8 Ms. spatially distributed is, relative abundances ≤0.1 10-8 5.2 10-8. suggest relation distribution shocks traced 2.12 μm H2 emission. Based carried out Interferometer. supported INSU/CNRS (France), MPG (Germany) IGN (Spain).A fits image HCOOCH3 integrated intensity map (Fig. 4) only available CDS via anonymous ftp cdsarc.u-strasbg.fr (130.79.128.5) http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/532/A32. All spectra can be obtained upon request authors.Table 10 Appendix electronic form http://www.aanda.org