Nitrogen hydrides in the cold envelope of IRAS 16293-2422

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 nitroge...

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Published in:Astronomy and astrophysics (Berlin) 2010-10, Vol.521, p.L52
Main Authors: Hily-Blant, P., Maret, S., Bacmann, A., Bottinelli, S., Parise, B., Caux, E., Faure, A., Bergin, E. A., Blake, G. A., Castets, A., Ceccarelli, C., Cernicharo, J., Coutens, A., Crimier, N., Demyk, K., Dominik, C., Gerin, M., Hennebelle, P., Henning, T., Kahane, C., Klotz, A., Melnick, G., Pagani, L., Schilke, P., Vastel, C., Wakelam, V., Walters, A., Baudry, A., Bell, T., Benedettini, M., Boogert, A., Cabrit, S., Caselli, P., Codella, C., Comito, C., Encrenaz, P., Falgarone, E., Fuente, A., Goldsmith, P. F., Helmich, F., Herbst, E., Jacq, T., Kama, M., Langer, W., Lefloch, B., Lis, D., Lord, S., Lorenzani, A., Neufeld, D., Nisini, B., Pacheco, S., Phillips, T., Salez, M., Saraceno, P., Schuster, K., Tielens, X., van der Tak, F., van der Wiel, M. H. D., Viti, S., Wyrowski, F., Yorke, H.
Format: Article
Language:English
Subjects:
astrochemistry
Astronomy
Astrophysics
Earth, ocean, space
Exact sciences and technology
ISM: abundances
ISM: general
Physics
Sciences of the Universe
Solar and Stellar Astrophysics
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Summary: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.
ISSN:0004-6361
1432-0746
1432-0756
DOI:10.1051/0004-6361/201015253