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Astron. Astrophys. 327, L9-L12 (1997)

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Letter to the Editor

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

R. Simon 1, J. Stutzki 1, A. Sternberg 2 and G. Winnewisser 1

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

Received 21 July 1997 / Accepted 7 August 1997

Abstract

We present fully sampled spectral line maps of the Orion Bar region observed simultaneously in the CN N=3 [FORMULA] 2 and CS J=7 [FORMULA] 6 rotational transitions with the JCMT at an angular resolution of [FORMULA]. We find that the CN emission specifically traces an intermediate cloud layer located between the peaks of vibrationally excited [FORMULA] and [FORMULA] 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 [FORMULA] [FORMULA] [FORMULA] 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 [FORMULA] /CN/CS is consistent with chemical stratification in an edge-on PDR in which high density gas ([FORMULA] [FORMULA] [FORMULA]) 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

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© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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