Letter to the Editor
Nitrogen hydrides in the cold envelope of IRAS 16293-2422 *,**
1
Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
2
Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, CNRS/INSU, UMR 5804, Floirac, France
3
Centre d'Étude Spatiale des Rayonnements, Université Paul Sabatier, Toulouse 3, CNRS UMR 5187, Toulouse, France
4
Max-Planck-Institut für Radioastronomie, Bonn, Germany
5
Department of Astronomy, University of Michigan, Ann Arbor, USA
6
California Institute of Technology, Pasadena, USA
7
Centro de Astrobiología, CSIC-INTA, Madrid, Spain
8
Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Amsterdam, The Netherlands
9
Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
10
LERMA, UMR 8112-CNRS, Ecole Normale Supérieure et Observatoire de
Paris, France
11
Max-Planck-Institut für Astronomie, Heidelberg, Germany
12
Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA
13
LERMA and UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
14
Physikalisches Institut, Universität zu Köln, Köln, Germany
15
INAF – Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
16
Infared Processing and Analysis Center, Caltech, Pasadena, USA
17
School of Physics and Astronomy, University of Leeds, Leeds UK
18
INAF Osservatorio Astrofisico di Arcetri, Florence Italy
19
IGN Observatorio Astronómico Nacional, Alcalá de Henares, Spain
20
Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
21
SRON Netherlands Institute for Space Research, Groningen, The Netherlands
22
Ohio State University, Columbus, OH, USA
23
Johns Hopkins University, Baltimore MD, USA
24
INAF – Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
25
Institut de RadioAstronomie Millimétrique, Grenoble, France
26
Leiden Observatory, Leiden University, Leiden, The Netherlands
27
Kapteyn Astronomical Institute, University of Groningen, The Netherlands
28
Department of Physics and Astronomy, University College London, London, UK
Received:
22
June
2010
Accepted:
2
September
2010
Nitrogen is the fifth most abundant element in the Universe, yet the gas-phase chemistry of N-bearing species remains poorly understood. Nitrogen hydrides are key molecules of nitrogen chemistry. Their abundance ratios place strong constraints on the production pathways and reaction rates of nitrogen-bearing molecules. We observed the class 0 protostar IRAS 16293-2422 with the heterodyne instrument HIFI, covering most of the frequency range from 0.48 to 1.78 THz at high spectral resolution. The hyperfine structure of the amidogen radical o-NH2 is resolved and seen in absorption against the continuum of the protostar. Several transitions of ammonia from 1.2 to 1.8 THz are also seen in absorption. These lines trace the low-density envelope of the protostar. Column densities and abundances are estimated for each hydride. We find that NH:NH2:NH3 ≈ 5:1:300. Dark clouds chemical models predict steady-state abundances of NH2 and NH3 in reasonable agreement with the present observations, whilst that of NH is underpredicted by more than one order of magnitude, even using updated kinetic rates. Additional modelling of the nitrogen gas-phase chemistry in dark-cloud conditions is necessary before having recourse to heterogen processes.
Key words: ISM: abundances / ISM: general / astrochemistry
Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.
Appendices (pages 6, 7) are only available in electronic form at http://www.aanda.org
© ESO, 2010