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Issue A&A
Volume 381, Number 1, January I 2002
Page(s) L17 - L20
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20011547



A&A 381, L17-L20 (2002)
DOI: 10.1051/0004-6361:20011547

Letter

The puzzling detection of D $_{\mathsf 2}$CO in the molecular cloud L1689N

C. Ceccarelli1, C. Vastel2, A. G. G. M. Tielens3, A. Castets1, A. C. A. Boogert4, L. Loinard5 and E. Caux2

1  Observatoire de Bordeaux, BP 89, 33270 Floirac, France
2  CESR CNRS-UPS, BP 4346, 31028 Toulouse Cedex 04, France
3  SRON, PO Box 800, 9700 AV Groningen, The Netherlands
4  California Institute of Technology, Downs Laboratory of Physics 320-47, Pasadena, CA 91125, USA
5  Instituto de Astronomía, UNAM, Apdo Postal 72-3 (Xangari), 58089 Morelia, Michoacán, México

(Received 11 October 2001 / Accepted 8 November 2001)

Abstract
We present new observations of the D 2CO emission towards the small cloud L1689N in the $\rho$ Ophiuchus complex. We surveyed five positions, three being a cut across a shock site and two probing the quiescent gas of the molecular cloud. We detected D 2CO emission in the first three positions. The measured [ D 2CO] /[ H 2CO] is about 3%, whereas it is $\leq$2% in the quiescent gas. We discuss the implications of these new observations, which suggest that the bulk of the D 2CO molecules is stored in grain mantles, and removed from the cold storage by the shock at the interface between the outflowing and quiescent gas. We review the predictions of the published models proposed to explain the observed high deuteration of formaldehyde. They fall in two basic schemes: gas phase and grain surface chemistry. None of the reviewed models is able to account for the observed [ D 2CO] /[ H 2CO] abundance ratio. A common characteristics shared by the models is apparently that all underestimate the atomic [D]/[H] ratio in the accreting gas.


Key words: ISM: abundances -- ISM: molecules -- stars: formation -- ISM: individual: L1689N

Offprint request: C. Ceccarelli, ceccarel@observ.u-bordeaux.fr

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