Issue |
A&A
Volume 521, October 2010
Herschel/HIFI: first science highlights
|
|
---|---|---|
Article Number | L31 | |
Number of page(s) | 5 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201015101 | |
Published online | 01 October 2010 |
Letter to the Editor
Ortho-to-para ratio of interstellar heavy water*
1
Centre d'Étude Spatiale des Rayonnements, Université Paul Sabatier, Toulouse, France
e-mail: vastel@cesr.fr
2
CNRS/INSU, UMR 5187, Toulouse, France
3
Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
4
Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, Floirac, France
5
CNRS/INSU, UMR 5804, Floirac Cedex, France
6
Centro de Astrobiologìa, CSIC-INTA, Madrid, Spain
7
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209-CNRS, Dijon Cedex, France
8
Department of Astronomy, University of Michigan, Ann Arbor, USA
9
California Institute of Technology, Pasadena, USA
10
Astronomical Institute Anton Pannekoek, University of Amsterdam, Amsterdam, The Netherlands
11
Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
12
Laboratoire d'Études du Rayonnement et de la Matière en Astrophysique, UMR 8112 CNRS/INSU, OP, ENS, UPMC, UCP, Paris, France
13
Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA
14
Max-Planck-Institut für Radioastronomie, Bonn, Germany
15
Physikalisches Institut, Universität zu Köln, Köln, Germany
16
INAF - Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
17
Infared Processing and Analysis Center, Caltech, Pasadena, USA
18
School of Physics and Astronomy, University of Leeds, Leeds, UK
19
INAF Osservatorio Astrofisico di Arcetri, Florence, Italy
20
IGN Observatorio Astronómico Nacional, Alcalá de Henares, Spain
21
Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
22
SRON Netherlands Institute for Space Research, Groningen, The Netherlands
23
Max-Planck-Institut für Astronomie, Heidelberg, Germany
24
Ohio State University, Columbus, OH, USA
25
Johns Hopkins University, Baltimore MD, USA
26
INAF - Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
27
Institut de RadioAstronomie Millimétrique, Grenoble, France
28
Leiden Observatory, Leiden University, Leiden, The Netherlands
29
Kapteyn Astronomical Institute, University of Groningen, The Netherlands
30
Department of Physics and Astronomy, University College London, London, UK
31
Chalmers University of Technology, Gøterborg, Sweden
Received:
28
May
2010
Accepted:
25
July
2010
Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular D/H ratios have been found in the environments of low-mass star-forming regions, and in particular the Class 0 protostar IRAS 16293-2422.
Aims. The CHESS (Chemical HErschel Surveys of Star forming regions) key
program aims to study the molecular complexity of the
interstellar medium. The high sensitivity and spectral resolution
of the Herschel/HIFI instrument provide a unique opportunity to observe the
fundamental 1-
transition of the ortho-D2O
molecule, which is inaccessible from the ground, and determine the
ortho-to-para D2O ratio.
Methods. We detected the fundamental transition of the ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in
absorption with a line opacity of 0.62 ± 0.11 (1σ). From the previous ground-based observations of the fundamental
1 – 1
transition of para-D2O seen in absorption at 316.80 GHz, we estimate a line opacity of 0.26 ± 0.05
(1σ).
Results. We show that the observed absorption is caused by the cold gas in the envelope of the protostar. Using these new observations, we estimate for the first time the ortho-to-para D2O ratio to be lower than 2.6 at a 3σ level of uncertainty, which should be compared with the thermal equilibrium value of 2:1.
Key words: astrochemistry / ISM: molecules / submillimeter: ISM / ISM: abundances / molecular processes / line: identification
© ESO, 2010
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