Protostars and Planets VI, Heidelberg, July 15-20, 2013
Modeling the evolution of ice deuteration during the formation of low-mass protostars
Taquet, Vianney (NASA Goddard Space Flight Center / NASA Postdoctoral Program)
Charnley, Steven (NASA Goddard Space Flight Center)
Cordiner, Martin (NASA Goddard Space Flight Center / The Catholic University of America)
Extremely large deuteration of several molecules has been observed around low-mass proto- stars for a decade. New observations performed with the Herschel Space Observatory or with ground- based interferometers have allowed astronomers to derive the D/H ratio of water, giving contrasting results (between less than 1e−3 to a few percents; Coutens et al. 2012, Persson et al. 2013, Visser et al. 2013, Taquet et al. 2013a). In previous studies, we have successfully reproduced the high deuteration of water derived by Coutens et al. (2012) with typical molecular cloud conditions and a low value for the H2 ortho/para ratio (opr < 1e−3; Taquet et al. 2013b). However, this result contrasts with the long timescale needed to decrease the H2 opr from its statistical value of 3 and, therefore, the non-detection of DCO+ towards interstellar clouds outside dense cores (see Pagani et al. 2011).
In this poster, we study the time-dependent and spatial evolutions of the H2 opr and the ice deuteration in the early-stages of low-mass star formation. For this purpose, we coupled our gas-grain astrochemical model (Taquet et al. 2012) with a simple dynamical model of core collapse leading to the formation of a central protostar (Whitworth & Ward-Thompson 2001). We present the first results of this work and show that we can reproduce the deuteration of various molecules both in prestellar cores and Class 0 protostars. In pre stellar cores, the deuteration of interstellar ices is limited to the few outermost layers. In Class 0 protostars, the deuteration of various molecules decreases with the age of the protostar and could explain the difference in the observations presented above.
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