US EPA

1451232 

Journal Article 

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

Parise, B; Du, F; Liu, FC; Belloche, A; Wiesemeyer, H; Guesten, R; Menten, KM; Huebers, HW; Klein, B 

2012 

Yes 

Astronomy & Astrophysics
ISSN: 0004-6361 

542 

10.1051/0004-6361/201218784 

WOS:000305803300077 

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 1(11)-0(00) 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 1(11)-0(00) line, provides an estimate of the
abundance ratio OD/HDO similar to 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. 

ISM: abundances; ISM: individual objects: IRAS 16293-2422; ISM: molecules; submillimeter: ISM; stars: formation