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Astron. Astrophys. 339, 553-560 (1998)

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Laboratory identification of the 4.62µm solid state absorption band in the ISO-SWS spectrum of RAFGL 7009S *

K. Demyk 1, E. Dartois 1, L. d'Hendecourt 1, M. Jourdain de Muizon 2, 3, A. M. Heras 4 and M. Breitfellner 5

1 IAS-CNRS, Université Paris XI, Batiment 121, F-91405 Orsay Cedex, France
2 DESPA, Observatoire de Paris, F-92190 Meudon, France
3 LAEFF-INTA, ESA Satellite tracking station, P.O. Box 50727, E-28080 Madrid, Spain
4 ISO Science Operation Centre, Astrophysics Division of ESA, P.O. Box 50727, E-28080 Madrid, Spain
5 ISO Science Operations, ESA/VILSPA Satellite tracking station, P.O. Box 50727, E-28080 Madrid, Spain

Received 5 January 1998 / Accepted 22 August 1998


We focus on the problem of the assignment of the "XCN" solid state feature observed in the spectra of numerous protostellar objects. This feature, located at 4.62µm has been tentatively identified with the molecular ion OCN-. New laboratory experiments have been performed in order to confirm this identification. OCN- is produced by UV photolysis of mixtures of CO:NH3 (1:1) deposited on a cold substrate. Simultaneously, the counterion [FORMULA] is also produced to balance the charge in the matrix. The use of electron donor and acceptor dopants incorporated in the mixtures allows us to reduce or enhance the production of the OCN- and [FORMULA] features, thus establishing their ionic character. The production of HNCO when an electron acceptor is used, and the formation of the OCN- band during thermal annealing, constitute convincing arguments in favour of the formation of OCN- and [FORMULA] by acid-base reactions where the acid HNCO transfers a proton to the base NH3. We consider the astrophysical implications for the interpretation of the ISO-SWS spectrum of the protostellar source RAFGL 7009S. In this source, the 4.62µm band is deep and large, although the derived abundance of this ion, relative to H2O ice, is on the order of 4%. Identification of OCN- is considered in several other sources. The contribution of [FORMULA] to the unidentified 6.85µm feature is discussed.

Key words: ISM: individual objects: RAFGL 7009S – ISM: molecules – ISM: abundances – molecular processes – dust, exctinction

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Send offprint requests to: K. Demyk, (demyk@ias.fr)

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© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998