A&A 402, L73-L76 (2003)
DOI: 10.1051/0004-6361:20030343

Letter

First detection of NH ( ) from a low mass cloud core

On the low ammonia abundance of the Oph A core

R. Liseau¹, B. Larsson¹, A. Brandeker¹, P. Bergman², P. Bernath³, J. H. Black², R. Booth², V. Buat⁴, C. Curry³, P. Encrenaz⁵, E. Falgarone⁶, P. Feldman⁷, M. Fich³, H. Florén¹, U. Frisk⁸, M. Gerin⁶, E. Gregersen⁹, J. Harju¹⁰, T. Hasegawa¹¹, Å. Hjalmarson², L. Johansson², S. Kwok¹¹, A. Lecacheux¹², T. Liljeström¹³, K. Mattila¹⁰, G. Mitchell¹⁴, L. Nordh¹⁵, M. Olberg², G. Olofsson¹, L. Pagani⁵, R. Plume¹¹, I. Ristorcelli¹⁶, Aa. Sandqvist¹, F. v. Schéele⁸, G. Serra¹⁶, N. Tothill¹⁴, K. Volk¹¹ and C. Wilson<sup>9

1</sup>  Stockholm Observatory, SCFAB, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
²  Onsala Space Observatory, 439 92 Onsala, Sweden
³  Department of Physics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
⁴  Laboratoire d'Astronomie Spatiale, BP 8, 13376 Marseille Cedex 12, France
⁵  LERMA & FRE 2460 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
⁶  LERMA & FRE 2460 du CNRS, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
⁷  Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
⁸  Swedish Space Corporation, PO Box 4207, 171 04 Solna, Sweden
⁹  Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada
¹⁰  Observatory, PO Box 14, University of Helsinki, 00014 Helsinki, Finland
¹¹  Department of Physics and Astronomy, University of Calgary, Calgary, ABT 2N 1N4, Canada
¹²  LESIA, Observatoire de Paris, Section de Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
¹³  Metsähovi Radio Observatory, Helsinki University of Technology, Otakaari 5A, 02150 Espoo, Finland
¹⁴  Department of Astronomy and Physics, Saint Mary's University, Halifax, NS B3H 3C3, Canada
¹⁵  Swedish National Space Board, Box 4006, 171 04 Solna, Sweden
¹⁶  CESR, 9 avenue du Colonel Roche, BP 4346, 31029 Toulouse, France

(Received 29 November 2002 / Accepted 1 February 2003)

Abstract
Odin has successfully observed the molecular core Oph A in the 572.5 GHz rotational ground state line of ammonia, NH ₃ ( ). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C ¹⁷O and CH ₃OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations of line excitation and transfer yields a quite ordinary abundance of methanol, X( . Unless NH ₃ is not entirely segregated from C ¹⁷O and CH ₃OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X( .

Key words: ISM: individual objects: -- clouds -- molecules -- stars: formation

Offprint request: R. Liseau, rene.liseau@astro.su.se

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