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Ortho-to-para ratio of interstellar heavy water

C. Vastel ; C. Ceccarelli ; E. Caux ; A. Coutens ; J. Cernicharo ; S. Bottinelli ; K. Demyk ; A. Faure ; L. Wiesenfeld ; Y. Scribano ; A. Bacmann ; P. Hily-Blant ; S. Maret ; A. Walters ; E. A. Bergin ; G. A. Blake ; A. Castets ; N. Crimier ; C. Dominik ; P. Encrenaz ; M. Gerin ; P. Hennebelle ; C. Kahane ; A. Klotz ; G. Melnick ; L. Pagani ; B. Parise ; P. Schilke ; V. Wakelam ; A. Baudry ; T. Bell ; M. Benedettini ; A. Boogert ; S. Cabrit ; P. Caselli ; C. Codella ; C. Comito ; E. Falgarone ; A. Fuente ; P. F. Goldsmith ; F. Helmich ; T. Henning ; E. Herbst ; T. Jacq ; M. Kama ; W. Langer ; B. Lefloch ; D. Lis ; S. Lord ; A. Lorenzani ; D. Neufeld ; B. Nisini ; S. Pacheco ; J. Pearson ; T. Phillips ; M. Salez ; P. Saraceno ; K. Schuster ; X. Tielens ; F. van der Tak ; M. H. D. van der Wiel ; S. Viti ; F. Wyrowski ; H. Yorke ; P. Cais ; J. M. Krieg ; Michael Olberg (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; L. Ravera
Astronomy and Astrophysics (0004-6361). Vol. 521 (2010), p. Article Number: L31 .
[Artikel, refereegranskad vetenskaplig]

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(1,1)-0(0,0) 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 (1 sigma). From the previous ground-based observations of the fundamental 1(1,0)-1(0,1) transition of para-D2O seen in absorption at 316.80 GHz, we estimate a line opacity of 0.26 +/- 0.05 (1 sigma). 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 3 sigma level of uncertainty, which should be compared with the thermal equilibrium value of 2:1.

Nyckelord: astrochemistry, ISM: molecules, submillimeter: ISM, ISM: abundances, molecular processes, line: identification, protostar iras 16293-2422, spectroscopy, constraints, envelope

Denna post skapades 2010-12-27. Senast ändrad 2015-06-23.
CPL Pubid: 131886


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Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium


Astronomi, astrofysik och kosmologi

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