Deuterated water in star-forming regions: contribution of the Herschel/HIFI spectroscopic data

Seminar Date: 
01 Oct 2012 - 14:00 to 15:00
Audrey Coutens
IRAP Toulouse

Note: the seminar will be held in RF016 (Rockefeller building at the Niels Bohr Institute)


Water is one of the most abundant molecules in the interstellar medium. In addition to being a primordial ingredient in the emergence of life, this species plays an essential role in the process of star formation through the cooling of warm gas. It also controls the chemistry for many species, either in the gas phase or on the grain surfaces. Studying its deuterated form HDO is a unique opportunity, through the estimation of the HDO/H2O ratio, to constrain the mechanisms of water formation and to better understand the origin of water contained in terrestrial oceans. Indeed, recent results obtained with the Herschel satellite show that the HDO/H2O ratio observed in comets is similar to the value measured in oceans (∼ 1.5 × 10−4), which suggests that comets could have brought a large fraction to Earth to form the oceans during heavy bombardments (Hartogh et al. 2011).


During my PhD thesis, I was interested in an earliest stage of star formation with the study in particular of the Class 0 protostar IRAS 16293. An unbiaised spectral survey was carried out towards this source with the HIFI instrument in the framework of the CHESS Herschel Key Program, allowing the detection of numerous HDO transitions. Additional transitions were also observed with ground based telescopes. Using radiative transfer models, it is then possible to constrain the HDO abundances. Similar work can be performed on H2-18O to estimate the H2O abundances. I will present in this seminar the results obtained for this source as well as for two other low-mass protostars NGC 1333 IRAS 4A and IRAS 4B. Preliminary results for the high mass star forming regions G34.26+0.15 studied in the framework of the Herschel Key Program PRISMAS will also be mentioned.