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Astron. Astrophys. 327, L9-L12

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Letter to the Editor

Chemical stratification in the Orion Bar region:
CN and CS submillimeter observations

R. Simon1, J. Stutzki1, A. Sternberg2, and G. Winnewisser1

1I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany
2School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel

Received 21 July 1997 / Accepted 7 August 1997


We present fully sampled spectral line maps of the Orion Bar region observed simultaneously in the CN N=3FORMULA2 and CS J=7FORMULA6 rotational transitions with the JCMT at an angular resolution of 14''. We find that the CN emission specifically traces an intermediate cloud layer located between the peaks of vibrationally excited H2 and HCO+ emission located closer to the ionization front, and CS emission originating closer to the cloud core. By comparing the observed spatial displacement of CN and CS emission with PDR models we infer a density of FORMULA105FORMULA for these cloud layers. This value is in agreement with the results of an escape probability radiative transfer analysis of our CN and CS line observations. We conclude that the observed distribution of H2/CN/CS is consistent with chemical stratification in an edge-on PDR in which high density gas (FORMULA105FORMULA) is distributed homogeneously.

Key words: ISM: abundances - ISM: clouds - ISM: individual objects: Orion Bar - ISM: molecules - ISM: structure - Radio lines: ISM

Send offprint requests to: R. Simon

© European Southern Observatory (ESO) 1997

Online publication: October 14, 1997
Last change: April 6, 1998