Nitrogen hydrides in the cold envelope of IRAS 16293-2422 [Letter]

Hily-Blant, P., Maret, S., Bacmann, A., Bottinelli, S., Parise, Berengere, 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. and Yorke, H. 2010. Nitrogen hydrides in the cold envelope of IRAS 16293-2422 [Letter]. Astronomy and Astrophysics 521 , L52. 10.1051/0004-6361/201015253

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Abstract

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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Uncontrolled Keywords:	ISM: abundances ; ISM: general ; astrochemistry
Additional Information:	Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/0004-6361/ (accessed 17/04/2014)
Publisher:	EDP Sciences
ISSN:	0004-6361
Date of First Compliant Deposit:	30 March 2016
Last Modified:	07 May 2023 10:33
URI:	https://orca.cardiff.ac.uk/id/eprint/52792

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