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24 April 2024

» arxiv » 1007.1466

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Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C
D. C. Lis ; T. G. Phillips ; P. F. Goldsmith ; D. A. Neufeld ; E. Herbst ; C. Comito ; P. Schilke ; H. S. P. Müller ; E. A. Bergin ; M. Gerin ; T. A. Bell ; M. Emprechtinger ; J. H. Black ; G. A. Blake ; F. Boulanger ; S. Cabrit ; E. Caux ; C. Ceccarelli ; J. Cernicharo ; A. Coutens ; N. R. Crockett ; F. Daniel ; E. Dartois ; M. De Luca ; M.-L. Dubernet ; P. Encrenaz ; E. Falgarone ; T. R. Geballe ; B. Godard ; T. F. Giesen ; J. R. Goicoechea ; C. Gry ; H. Gupta ; P. Hennebelle ; P. Hily-Blant ; R. Kołos ; J. Krełowski ; C. Joblin ; D. Johnstone ; M. Kaźmierczak ; S. D. Lord ; S. Maret ; P. G. Martin ; J. Martín-Pintado ; G. J. Melnick ; K. M. Menten ; R. Monje ; B. Mookerjea ; P. Morris ; J. A. Murphy ; V. Ossenkopf ; L. Pagani ; J. C. Pearson ; M. Pérault ; C. Persson ; R. Plume ; S.-L. Qin ; M. Salez ; S. Schlemmer ; M. Schmidt ; P. Sonnentrucker ; J. Stutzki ; D. Teyssier ; N. Trappe ; F. F. S. van der Tak ; C. Vastel ; S. Wang ; H. W. Yorke ; S. Yu ; J. Zmuidzinas ; A. Boogert ; N. Erickson ; A. Karpov ; J. Kooi ; F. W. Maiwald ; R. Schieder ; P. Zaal ;
Date:	8 Jul 2010
Abstract:	We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H$_2^{16}$O and H$_2^{18}$O in absorption towards Sagittarius~B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of $2.35 pm 0.35$, corresponding to a spin temperature of $sim$27~K, towards Sagittarius~B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust.
Source:	arXiv, 1007.1466
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