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Detection of OD towards the low-mass protostar IRAS 16293-2422 [Letter]

Parise, Berengere, Du, F., Liu, F. -C., Belloche, A., Wiesemeyer, H., Güsten, R., Menten, K. M., Huebers, H. -W. and Klein, B. 2012. Detection of OD towards the low-mass protostar IRAS 16293-2422 [Letter]. Astronomy and Astrophysics 542 , L5. 10.1051/0004-6361/201218784

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Context. Although water is an essential and widespread molecule in star-forming regions, its chemical formation pathways are still not very well constrained. Observing the level of deuterium fractionation of OH, a radical involved in the water chemical network, is a promising way to infer its chemical origin. Aims. We aim at understanding the formation mechanisms of water by investigating the origin of its deuterium fractionation. This can be achieved by observing the abundance of OD towards the low-mass protostar IRAS 16293−2422, where the HDO distribution is already known. Methods. Using the GREAT receiver on board SOFIA, we observed the ground-state OD transition at 1391.5 GHz towards the low-mass protostar IRAS 16293−2422. We also present the detection of the HDO 111-000 line using the APEX telescope. We compare the OD/HDO abundance ratio inferred from these observations with the predictions of chemical models. Results. The OD line is detected in absorption towards the source continuum. This is the first detection of OD outside the solar system. The SOFIA observation, coupled to the observation of the HDO 111-000 line, provides an estimate of the abundance ratio OD/HDO ~ 17–90 in the gas where the absorption takes place. This value is fairly high compared with model predictions. This may be reconciled if reprocessing in the gas by means of the dissociative recombination of H2DO+ further fractionates OH with respect to water. Conclusions. The present observation demonstrates the capability of the SOFIA/GREAT instrument to detect the ground transition of OD towards star-forming regions in a frequency range that was not accessible before. Dissociative recombination of H2DO+ may play an important role in setting a high OD abundance. Measuring the branching ratios of this reaction in the laboratory will be of great value for chemical models.

Item Type: Article
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: ISM: abundances ; ISM: individual objects: IRAS 16293-2422 ; ISM: molecules ; submillimeter: ISM ; stars: formation
Additional Information: Pdf uploaded in accordance with publisher's policy at (accessed 16/04/2014)
Publisher: EDP Sciences
ISSN: 0004-6361
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 09:40

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