Letter to the Editor

First detection of NH₃ () from a low mass cloud core ^*,**

On the low ammonia abundance of the ρ  Oph A core

¹ 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

Corresponding author: R. Liseau, rene.liseau@astro.su.se

Received: 29 November 2002
Accepted: 1 February 2003

Abstract

Odin has successfully observed the molecular core ρ  Oph A in the 572.5 GHz rotational ground state line of ammonia, NH₃ (). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C¹⁷O and CH₃OH) 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 NH₃ is not entirely segregated from C¹⁷O and CH₃OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X(.