Nitrogen hydrides in the cold envelope of IRAS 16293-2422

Pierre Hily-Blant (1) , S. Maret (1) , A. Bacmann (1, 2, 3, 4, 5) , S. Bottinelli (6) , B. Parise (6) , E. Caux (6) , A. Faure (1) , E. A. Bergin (7) , G. A. Blake (8) , Alain Castets (1) , C. Ceccarelli (1) , J. Cernicharo (9) , A. Coutens (1) , N. Crimier (1) , K. Demyk (1) , C. Dominik (10) , M. Gerin (11, 12) , P. Hennebelle (1) , T. Henning (13) , C. Kahane (1) , A. Klotz (6, 14) , G. Melnick (1) , L. Pagani (11) , P. Schilke (15) , C. Vastel (6) , Valentine Wakelam (2, 3, 4, 5) , A. Walters (1) , Alain Baudry (2, 3, 4, 5) , T. Bell (1) , M. Benedettini (1) , A. Boogert (1) , S. Cabrit (11) , P. Caselli (16) , C. Codella (1) , C. Comito (17) , P. Encrenaz (11) , E. Falgarone (12) , A. Fuente (1) , P. F. Goldsmith , F. Helmich (1) , E. Herbst (18) , T. Jacq (2, 3, 4, 5) , M. Kama (1) , W. Langer (1) , B. Lefloch (1) , D. Lis (1) , S. Lord (1) , A. Lorenzani (16) , D. Neufeld (1) , B. Nisini (19) , S. Pacheco (1) , T. Phillips (1) , M. Salez (1) , P. Saraceno (20) , K. Schuster (1) , X. Tielens (1) , F. van Der Tak (1) , M. H. D. van Der Wiel , S. Viti (1) , F. Wyrowski (15) , H. Yorke (1)

1 LAOG - Laboratoire d'Astrophysique de Grenoble
2 LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]
3 OASU - Observatoire aquitain des sciences de l'univers
4 UB - Université Sciences et Technologies - Bordeaux 1
5 L3AB - Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux
6 CESR - Centre d'étude spatiale des rayonnements
7 CfA - Harvard-Smithsonian Center for Astrophysics
8 LOCIE - LabOratoire proCédés énergIe bâtimEnt
9 CSIC - Centro de Investigaciones Biológicas
10 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
11 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
12 LRA - Laboratoire de Radioastronomie
13 MPIA - Max-Planck-Institut für Astronomie
14 OHP - Observatoire de Haute-Provence
15 MPIFR - Max-Planck-Institut für Radioastronomie
16 OAA - INAF - Osservatorio Astrofisico di Arcetri
17 CASSIOPEE - Laboratoire de Cosmologie, Astrophysique Stellaire & Solaire, de Planétologie et de Mécanique des Fluides
18 OSU - Ohio State University [Columbus]
19 OAR - INAF - Osservatorio Astronomico di Roma
20 IFSI - Istituto di Fisica dello Spazio Interplanetario

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. 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

Mots clés: ISM: abundances; ISM: general; astrochemistry

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]; Astrophysique stellaire et solaire [astro-ph.SR]

Pierre Hily-Blant, S. Maret, A. Bacmann, S. Bottinelli, B. Parise, et al.. Nitrogen hydrides in the cold envelope of IRAS 16293-2422. Astronomy and Astrophysics - A&A, 2010, 521, pp.L52. ⟨10.1051/0004-6361/201015253⟩. ⟨hal-00541827⟩