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2010A&A...521L..31V - Astronomy and Astrophysics, volume 521, L31-31 (2010/10-1)

Ortho-to-para ratio of interstellar heavy water.

VASTEL C., CECCARELLI C., CAUX E., COUTENS A., CERNICHARO J., BOTTINELLI S., DEMYK K., FAURE A., WIESENFELD L., SCRIBANO Y., BACMANN A., HILY-BLANT P., MARET S., WALTERS A., BERGIN E.A., BLAKE G.A., CASTETS A., CRIMIER N., DOMINIK C., ENCRENAZ P., GERIN M., HENNEBELLE P., KAHANE C., KLOTZ A., MELNICK G., PAGANI L., PARISE B., SCHILKE P., WAKELAM V., BAUDRY A., BELL T., BENEDETTINI M., BOOGERT A., CABRIT S., CASELLI P., CODELLA C., COMITO C., FALGARONE E., FUENTE A., GOLDSMITH P.F., HELMICH F., HENNING T., HERBST E., JACQ T., KAMA M., LANGER W., LEFLOCH B., LIS D., LORD S., LORENZANI A., NEUFELD D., NISINI B., PACHECO S., PEARSON J., PHILLIPS T., SALEZ M., SARACENO P., SCHUSTER K., TIELENS X., VAN DER TAK F., VAN DER WIEL M.H.D., VITI S., WYROWSKI F., YORKE H., CAIS P., KRIEG J.-M., OLBERG M. and RAVERA L.

Abstract (from CDS):

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. 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. We detected the fundamental transition of the ortho-D2O molecule at 607.35GHz 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 316.80GHz, we estimate a line opacity of 0.26±0.05 (1σ). 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.

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Journal keyword(s): astrochemistry - ISM: molecules - submillimeter: ISM - ISM: abundances - molecular processes - line: identification

Simbad objects: 1

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