EDP Sciences
Free access
Issue
A&A
Volume 393, Number 3, October III 2002
Page(s) L49 - L53
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20021131


A&A 393, L49-L53 (2002)
DOI: 10.1051/0004-6361:20021131

Letter

Detection of doubly-deuterated methanol in the solar-type protostar IRAS 16293-2422

B. Parise1, C. Ceccarelli2, 3, A. G. G. M. Tielens4, E. Herbst5, B. Lefloch3, E. Caux1, A. Castets2, I. Mukhopadhyay6, L. Pagani7 and L. Loinard8

1  CESR CNRS-UPS, BP 4346, 31028 Toulouse Cedex 04, France
2  Observatoire de Bordeaux, BP 89, 33270 Floirac, France
3  Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 09, France
4  SRON, PO Box 800, 9700 AV Groningen, The Netherlands
5  Department of Physics, The Ohio State University, 174 W. 18th Ave. Columbus, OH 43210-1106, USA
6  College of Natural Sciences, Dakota State University, Madison, SD 57042-1799, USA
7  LERMA & FRE 2460 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire de Paris, 75014 Paris, France
8  Instituto de Astronomía, UNAM, Apdo Postal 72-3 (Xangari), 58089 Morelia, Michoacán, México

(Received 28 June 2002 / Accepted 2 August 2002)

Abstract
We report the first detection of doubly-deuterated methanol (CHD 2OH), as well as firm detections of the two singly-deuterated isotopomers of methanol (CH 2DOH and CH 3OD), towards the solar-type protostar IRAS 16293-2422. From the present multifrequency observations, we derive the following abundance ratios: $\rm [CHD_2OH]/[CH_3OH] = 0.2 \pm 0.1$, $\rm [CH_2DOH]/[CH_3OH] = 0.9
\pm 0.3$ , $\rm [CH_3OD]/[CH_3OH] = 0.04 \pm 0.02$. The total abundance of the deuterated forms of methanol is greater than that of its normal hydrogenated counterpart in the circumstellar material of IRAS 16293-2422, a circumstance not previously encountered. Formaldehyde, which is thought to be the chemical precursor of methanol, possesses a much lower fraction of deuterated isotopomers (~20%) with respect to the main isotopic form in IRAS 16293-2422. The observed fractionation of methanol and formaldehyde provides a severe challenge to both gas-phase and grain-surface models of deuteration. Two examples of the latter model are roughly in agreement with our observations of CHD 2OH and CH 2DOH if the accreting gas has a large (0.2-0.3) atomic D/H ratio. However, no gas-phase model predicts such a high atomic D/H ratio, and hence some key ingredient seems to be missing.


Key words: ISM: abundances -- ISM: molecules -- stars: formation -- ISM: individual: IRAS 16293-2422

Offprint request: B. Parise, Berengere.Parise@cesr.fr



© ESO 2002