Protostars and Planets VI, Heidelberg, July 15-20, 2013
Resolving the Chemical Substructure of Orion-KL
Feng, Siyi (Max-Planck-Institut für Astronomie)
Beuther, Henrik (Max-Planck-Institut für Astronomie)
Semenov, Dmitry (Max-Planck-Institut für Astronomie)
Henning, Thomas (Max-Planck-Institut für Astronomie)
Palau, Aina (Institut de Ciències de L`espai)
【Context】 The Kleinmann-Low nebula in Orion (Orion-KL) is the closest example of a high-mass star forming environment. Studying the resolved chemical structure of this complex region can provide important insight for relating the chemistry of high mass star forming regions with their evolutionary state. We present a line survey of Orion-KL obtained from the combined Submillimeter Array (SMA) and IRAM 30 m single-dish data. Covering 4 GHz bandwidth in total, this survey contains at least 160 emission lines from 27 chemical species.
【Aims】 The goal of this work is to resolve the molecular line emission from individual substructure in Orion-KL at high spectral and spatial resolution, inferring the chemical properties of the associated gas.
Methods. The spectra from different substructures are extracted and the intensity-integrated distribution maps for different molecules are imaged. We then calculate column densities, and abundances for each molecule in each identified substructure, assuming local thermal equilibrium (LTE), and that the lines are both optically thin and have uniform widths for all species.
【Results】 By complementing interferometric data of the Orion-KL region with single-dish data to recover the short spacing information, we are able to study spatial abundance variations in this region for the first time. On one hand, at the spatial resolution of 4 arcsec, several substructures appear on the continuum map. The strongest emission from nitrogen-bearing molecules comes from the main hot core, which has chemistry typical of an active region, while sulfur-bearing and carbon monoxides have extended emission covering the cooler southern ridge and outflow regions. In contrast, the distribution of saturated complex organics is more complicated. Most of them peak at either the hot core (e.g., CH3OH) or the compact ridge (e.g., HCOOCH3), while others peak at intermediate positions between the hot core and the compact ridge (e.g., CH3CH2OH). But nevertheless, no clear distinction can classify them in different groups yet. In addition, the chemistry within the outflow lobes does not appear to differ significantly from low-mass chemically active outflows, but the low-velocity outflow exhibits stronger emission from H2 and tracers like 34SO2, SO2, O13CS, 13CS than the high-velocity one, indicating stronger shocks. On the other hand, the high sensitivity of the dataset allows us to identify and spatially locate such weak complex molecules in Orion-KL as CH3COCH3, CH3OCH3, CH3CH2OH and, tentatively detected long carbon chain molecules like C6H & HC7N. These new features in hot core chemistry and outflow chemistry, indicated by the quantitative differences in molecular abundances from our data, will be important for interpreting molecular spectra from other high mass star forming regions.
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