Volume 531, July 2011
|Number of page(s)||5|
|Published online||04 July 2011|
Letter to the Editor
Institute for Astronomy, ETH Zurich, 8093 Zurich, Switzerland
2 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
3 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
4 Université de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 33271 Floirac Cedex, France
5 CNRS, UMR 5804, Laboratoire d’Astrophysique de Bordeaux, 2 rue de l’Observatoire, BP 89, 33271 Floirac Cedex, France
6 Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
7 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
8 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
9 Departamento de Astrofísica, Centro de Astrobiología (CSIC-INTA), 28850, Madrid, Spain
10 Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
Received: 15 March 2011
Accepted: 25 May 2011
OH is an important molecule in the H2O chemistry and the cooling budget of star-forming regions. The goal of the Herschel key program “Water In Star-forming regions with Herschel” (WISH) is to study H2O and related species during protostellar evolution. Our aim in this Letter is to assess the origin of the OH emission from star-forming regions and constrain the properties of the emitting gas. High-resolution observations of the OH triplet at 1837.8 GHz (163.1 μm) towards the high-mass star-forming region W3 IRS 5 with the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel reveal the first hyperfine velocity-resolved OH far-infrared spectrum of a star-forming region. The line profile of the OH emission shows two components: a narrow component (FWHM ≈ 4−5 km s-1) with partially resolved hyperfine structure resides on top of a broad (FWHM ≈ 30 km s-1) component. The narrow emission agrees well with results from radiative transfer calculations of a spherical envelope model for W3 IRS 5 with a constant OH abundance of xOH ≈ 8 × 10-9. Comparison with H2O yields OH/H2O abundance ratios of around 10-3 for T ≳ 100 K and around unity for T ≲ 100 K, consistent with the current picture of the dense cloud chemistry with freeze-out and photodesorption. The broad component is attributed to outflow emission. An abundance ratio of OH/H2O ≳ 0.028 in the outflow is derived from comparison with results of water line modeling. This ratio can be explained by a fast J-type shock or a slower UV-irradiated C-type shock.
Key words: astrochemistry / stars: formation / ISM: magnetic fields / ISM: jets and outflows / ISM: individual objects: W3 IRS 5
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2011
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