Issue |
A&A
Volume 388, Number 3, June IV 2002
|
|
---|---|---|
Page(s) | L53 - L56 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20020647 | |
Published online | 10 June 2002 |
Letter to the Editor
Triply deuterated ammonia in NGC 1333
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
Corresponding author: F. F. S. van der Tak, vdtak@mpifr-bonn.mpg.de
Received:
1
April
2002
Accepted:
24
April
2002
The Caltech Submillimeter Observatory has detected triply
deuterated ammonia, ND3, through its
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 ND3 are
cm-2 for Tex = 10 K and twice as high for
Tex = 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 ND3 abundance is
if ND3/H2 is constant throughout the envelope. In the more
likely case that ND3/H2D+ is constant, ND3/H2 peaks in the
cold outer parts of the source at a value of
. To reproduce the observed NH3/ND3 abundance ratio
of ~1000, grain surface chemistry requires an atomic D/H ratio
of ≈0.15 in the gas phase, >10 times higher than in recent
chemical models. More likely, the deuteration of NH3 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
© ESO, 2002
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