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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2010

Ortho-to-para ratio of interstellar heavy water

A. Coutens
J. Cernicharo
A. Faure
L. Wiesenfeld
Y. Scribano
  • Fonction : Auteur
S. Maret
C. Dominik
P. Hennebelle
Valentine Wakelam
  • Fonction : Auteur
  • PersonId : 828581
Alain Baudry
  • Fonction : Auteur
  • PersonId : 853057
P. Caselli
A. Fuente
P. F. Goldsmith
  • Fonction : Auteur
T. Henning
T. Jacq
  • Fonction : Auteur
B. Lefloch
B. Nisini
Justin Pearson
  • Fonction : Auteur
  • PersonId : 829524
M. H. D. van Der Wiel
  • Fonction : Auteur
J. M. Krieg
  • Fonction : Auteur

Résumé

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 11,1-00,0 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 11,0-10,1 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. Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.

Dates et versions

hal-00633418 , version 1 (18-10-2011)

Identifiants

Citer

C. Vastel, C. Ceccarelli, E. Caux, A. Coutens, J. Cernicharo, et al.. Ortho-to-para ratio of interstellar heavy water. Astronomy and Astrophysics - A&A, 2010, 521, pp.L31. ⟨10.1051/0004-6361/201015101⟩. ⟨hal-00633418⟩
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