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Issue A&A
Volume 388, Number 3, June IV 2002
Page(s) L53 - L56
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20020647



A&A 388, L53-L56 (2002)
DOI: 10.1051/0004-6361:20020647

Letter

Triply deuterated ammonia in NGC 1333

F. F. S. van der Tak1, P. Schilke1, H. S. P. Müller2, D. C. Lis3, T. G. Phillips3, M. Gerin4, 5 and E. Roueff5

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2  I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany
3  California Institute of Technology, Downs Laboratory of Physics 320-47, Pasadena, CA 91125, USA
4  Lab. de Radioastronomie Millimétrique, Dépt. de Physique de l'E.N.S., 24 rue Lhomond, 75231 Paris, France
5  DEMIRM, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France

(Received 1 April 2002 / Accepted 24 April 2002 )

Abstract
The Caltech Submillimeter Observatory has detected triply deuterated ammonia, ND 3, through its $J_K=1_0^{\rm a}\to0_0^{\rm s}$ transition near 310 GHz. Emission is found in the NGC 1333 region, both towards IRAS 4A and a position to the South-East where DCO + peaks. In both cases, the hyperfine ratio indicates that the emission is optically thin. Column densities of ND 3 are $3{-}6\times 10^{11}$ cm -2 for $T_{\rm ex}$ = 10 K and twice as high for $T_{\rm ex}$ = 5 K. Using a Monte Carlo radiative transfer code and a model of the structure of the IRAS source with temperature and density gradients, the estimated ND 3 abundance is $3.2\times 10^{-12}$ if ND 3/H 2 is constant throughout the envelope. In the more likely case that ND 3/H 2D + is constant, ND 3/H 2 peaks in the cold outer parts of the source at a value of $1.0\times 10^{-11}$ . To reproduce the observed NH 3/ND 3 abundance ratio of ~1000, grain surface chemistry requires an atomic D/H ratio of $\approx$0.15 in the gas phase, >10 times higher than in recent chemical models. More likely, the deuteration of NH 3 occurs by ion-molecule reactions in the gas phase, in which case the data indicate that deuteron transfer reactions are much faster than proton transfers.


Key words: ISM: abundances -- ISM: molecules

Offprint request: F. F. S. van der Tak, vdtak@mpifr-bonn.mpg.de

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