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Volume 488, Number 2, September III 2008
Page(s) 559 - 564
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:200809952
Published online 22 May 2008

A&A 488, 559-564 (2008)
DOI: 10.1051/0004-6361:200809952

An upper limit of gaseous water abundance in Chamaeleon-MMS1 as observed with ODIN

A. Klotz1, J. Harju2, I. Ristorcelli1, M. Juvela2, N. Boudet1, and L. K. Haikala2

1  CESR, Observatoire Midi-Pyrénées (CNRS-UPS), Université de Toulouse, BP 4346, 31028 Toulouse Cedex 04, France
    e-mail: klotz@cesr.fr
2  Observatory, PO Box 14, 00014 University of Helsinki, Finland

Received 11 April 2008 / Accepted 14 May 2008

Context. The determination of the gaseous water abundances in different intestellar environments is crucial for understanding the oxygen chemistry and its role in the molecular cloud evolution.
Aims. The purpose of this study is to estimate water abundance in the protostellar core Cha-MMS1.
Methods. The ground-state line of o-H20 at 557 GHz was observed with the ODIN telescope. Two observing runs performed in 2002 and 2003 resulted in an upper limit of $T_{\rm A}$ = 16 mK. A model for the core density and temperature structure was constructed using a 1.3 mm continuum map from SEST/SIMBA. The water abundance profile through the cloud was derived and water line intensities expected from this model were calculated.
Results. An upper limit of 7 $\times$ 10-9 was derived for the average fractional o-H2O abundance (relative to H2). The non-detection is consistent with an abundance profile where a high fractional abundance (~ 10-7) is reached in the low-density envelope of the core. According to our radiative transfer calculations, the detection of the 557 GHz line from a quiescent core should severely be hampered by self-absorption. Therefore the present observations do not put hard contrainst on the H2O abundance.

Key words: ISM: clouds -- ISM: individual objects: Chamaeleon-MMS1 -- ISM: abundances -- stars: formation

© ESO 2008