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First detection of ND in the solar-mass protostar IRAS16293-2422 [Letter]

Bacmann, A., Caux, E., Hily-Blant, P., Parise, Berengere, Pagani, L., Bottinelli, S., Maret, S., Vastel, C., Ceccarelli, C., Cernicharo, J., Henning, T., Castets, A., Coutens, A., Bergin, E. A., Blake, G. A., Crimier, N., Demyk, K., Dominik, C., Gerin, M., Hennebelle, P., Kahane, C., Klotz, A., Melnick, G., Schilke, P., 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., Pearson, J., Phillips, T., Salez, M., Saraceno, P., Schuster, K., Tielens, X., van der Tak, F. F. S., van der Wiel, M. H. D., Viti, S., Wyrowski, F., Yorke, H., Faure, A., Benz, A., Coeur-Joly, O., Cros, A., Guesten, R. and Ravera, L. 2010. First detection of ND in the solar-mass protostar IRAS16293-2422 [Letter]. Astronomy and Astrophysics 521 , L42. 10.1051/0004-6361/201015102

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Context. In the past decade, much progress has been made in characterising the processes leading to the enhanced deuterium fractionation observed in the ISM and in particular in the cold, dense parts of star forming regions such as protostellar envelopes. Very high molecular D/H ratios have been found for saturated molecules and ions. However, little is known about the deuterium fractionation in radicals, even though simple radicals often represent an intermediate stage in the formation of more complex, saturated molecules. The imidogen radical NH is such an intermediate species for the ammonia synthesis in the gas phase. Many of these light molecules however have their fundamental transitions in the submillimetre domain and their detection is hampered by the opacity of the atmosphere at these wavelengths. Herschel/HIFI represents a unique opportunity to study the deuteration and formation mechanisms of species not observable from the ground. Aims. We searched here for the deuterated radical ND in order to determine the deuterium fractionation of imidogen and constrain the deuteration mechanism of this species. Methods. We observed the solar-mass Class 0 protostar IRAS16293-2422 with the heterodyne instrument HIFI in Bands 1a (480–560 GHz), 3b (858–961 GHz), and 4a (949–1061 GHz) as part of the Herschel key programme CHESS (Chemical HErschel Survey of Star forming regions). Results. The deuterated form of the imidogen radical ND was detected and securely identified with 2 hyperfine component groups of its fundamental transition (N = 0–1) at 522.1 and 546.2 GHz, in absorption against the continuum background emitted from the nascent protostar. The 3 groups of hyperfine components of its hydrogenated counterpart NH were also detected in absorption. The absorption arises from the cold envelope, where many deuterated species have been shown to be abundant. The estimated column densities are ~2 × 1014 cm-2 for NH and ~ 1.3 × 1014 cm-2 for ND. We derive a very high deuterium fractionation with an [ND]/[NH] ratio of between 30 and 100%. Conclusions. The deuterium fractionation of imidogen is of the same order of magnitude as that in other molecules, which suggests that an efficient deuterium fractionation mechanism is at play. We discuss two possible formation pathways for ND, by means of either the reaction of N+ with HD, or deuteron/proton exchange with NH.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: ISM: molecules ; stars: formation
Additional Information: Pdf uploaded in accordance with publisher's policy at (accessed 17/04/2014)
Publisher: EDP Sciences
ISSN: 0004-6361
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 09:41

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