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A study of deuterated water in the low-mass protostar IRAS16293-2422 | Audrey Coutens
; Charlotte Vastel
; Emmanuel Caux
; Cecilia Ceccarelli
; Sandrine Bottinelli
; Laurent Wiesenfeld
; Alexandre Faure
; Yohann Scribano
; Claudine Kahane
; | Date: |
9 Jan 2012 | Abstract: | Our aim is to determine precisely the abundance distribution of HDO towards
the low-mass protostar IRAS16293-2422 and learn more about the water formation
mechanisms by the determination of the HDO/H2O abundance ratio. A spectral
survey of the source IRAS16293-2422 has been carried out in the framework of
the CHESS Herschel Key program with the HIFI instrument, allowing the detection
of numerous HDO lines. Other transitions were previously observed with
ground-based telescopes in the framework of TIMASSS. The spherical Monte Carlo
radiative transfer code RATRAN has been used to reproduce the observed line
profiles of HDO assuming an abundance jump, corresponding to the sublimation of
the molecules trapped on the icy grain mantles in the hot corino. To determine
the H2O abundance throughout the envelope, a similar study has been applied to
the H2-18O observed lines, as the H2O main isotope lines are contaminated by
the outflows. We derive an inner HDO abundance of 1.7e-7 and an outer HDO
abundance of 8e-11. To reproduce the HDO absorption lines, it is necessary to
add an absorbing layer in front of the envelope. It may correspond to a
water-rich layer created by the photodesorption of the ices at the edges of the
molecular cloud. The HDO/H2O ratio is ~1.4-5.8% in the hot corino whereas it is
~0.2-2.2% in the outer envelope. It is estimated at ~4.8% in the added
absorbing layer. Although it is clearly higher than the cosmic D/H abundance,
the HDO/H2O ratio remains lower than the D/H ratio derived for other deuterated
molecules observed in the same source. The similar ratios derived in the hot
corino and in the added absorbing layer suggests that water formed before the
gravitational collapse of the protostar, contrary to formaldehyde and methanol
which formed later once the CO molecules have depleted on the grains. | Source: | arXiv, 1201.1785 | Services: | Forum | Review | PDF | Favorites |
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