Protostars and Planets VI, Heidelberg, July 15-20, 2013
Deuterated water in low-mass protostars
Coutens, Audrey (Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen, Denmark)
Vastel, Charlotte (Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS-OMP, CNRS, France)
the CHESS, WISH and HEXOS collaboration, ()
In addition to its dominant role in the cooling of warm gas and in the oxygen chemistry, water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. Observations of deuterated water are an important complement for studies of H2O to understand how water forms and how it has evolved from cold prestellar cores to protoplanetary disks and consequently oceans for the Earth’s specific, but probably not isolated, case.
Several deuterated water transitions were observed with the Herschel/HIFI (Heterodyne Instrument for Far Infrared) instrument towards three low-mass protostars: IRAS 16293-2422, NGC1333 IRAS4A and NGC1333 IRAS4B. In the first source, both HDO and D2O lines are detected, thanks to the unbiased spectral survey carried out by the CHESS key program (Vastel et al. 2010, Coutens et al. 2013a). In the framework of a collaboration between the CHESS, WISH and HEXOS programs, two HDO key lines were observed towards the two other protostars. In addition, complementary observations were carried out with several ground-based single-dish telescopes (IRAM-30m, JCMT, APEX).
We used the non-LTE RATRAN spherical model (Hogerheijde & van der Tak 2000) to determine the HDO abundance distribution throughout the protostellar envelope. An abundance jump at 100 K is required to reproduce the line profiles. Indeed, water molecules trapped in the icy grain mantles thermally desorb in the hot corinos, the inner warm regions of the protostellar envelopes. We also obtain that it is necessary to add a water-rich external absorbing layer to reproduce the absorbing components of the HDO and D2O fundamental transitions in all sources (Coutens et al. 2012, 2013a,b). The results derived for the different sources will be then presented and discussed.
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