title: Herschel/HIFI observations of the circumstellar ammonia lines in IRC+10216.
abstract: A discrepancy exists between the abundance of ammonia (NH3) derived previously for the circumstellar envelope (CSE) of IRC+10216 from far-IR submillimeter rotational lines and that inferred from radio inversion or mid-infrared (MIR) absorption transitions.
  
  
  
  To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho- and para-NH3transitions toward IRC+10216 were obtained withHerschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3in the envelope of IRC+10216.
  
  
  
  We used the Heterodyne Instrument for the Far Infrared (HIFI) on boardHerschelto observe all rotational transitions up to theJ= 3 level (three ortho- and six para-NH3lines). We conducted non-LTE multilevel radiative transfer modelling, including the effects of near-infrared (NIR) radiative pumping through vibrational transitions. The computed emission line profiles are compared with the new HIFI data, the radio inversion transitions, and the MIR absorption lines in theν2band taken from the literature.
  
  
  
  We found that NIR pumping is of key importance for understanding the excitation of rotational levels of NH3. The derived NH3abundances relative to molecular hydrogen were (2.8 ± 0.5) × 10-8for ortho-NH3and [Formula: see text] for para-NH3, consistent with an ortho/para ratio of 1. These values are in a rough agreement with abundances derived from the inversion transitions, as well as with the total abundance of NH3inferred from the MIR absorption lines. To explain the observed rotational transitions, ammonia must be formed near to the central star at a radius close to the end of the wind acceleration region, but no larger than about 20 stellar radii (1σconfidence level).
authors.affiliation: N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland.
authors.forename: M R
authors.initials: MR
authors.lastname: Schmidt
authors.affiliation: Key Laboratory for the Structure and Evolution of Celestial Objects, Yunnan Observatories, Chinese Academy of Sciences, P.O. Box 110, Kunming, Yunnan Province, China.
authors.forename: J H
authors.initials: JH
authors.lastname: He
authors.affiliation: N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland.
authors.forename: R
authors.initials: R
authors.lastname: Szczerba
authors.affiliation: Observatorio Astronómico Nacional. Ap 112, E-28803 Alcalá de Henares, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Bujarrabal
authors.affiliation: Observatorio Astronómico Nacional (IGN), Alfonso XII N°3, E-28014 Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Alcolea
authors.affiliation: ICMM, CSIC, group of Molecular Astrophysics, C/Sor Juana Inés de la Cruz N3, 28049 Cantoblanco (Madrid), Spain.
authors.forename: J
authors.initials: J
authors.lastname: Cernicharo
authors.affiliation: Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium; Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 Amsterdam, The Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Decin
authors.affiliation: Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, S-439 92 Onsala, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Justtanont
authors.affiliation: European Space Astronomy Centre, ESA, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid, Spain.
authors.forename: D
authors.initials: D
authors.lastname: Teyssier
authors.affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany.
authors.forename: K M
authors.initials: KM
authors.lastname: Menten
authors.affiliation: Johns Hopkins Universtity, Baltimore, MD 21218, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Neufeld
authors.affiliation: Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, S-439 92 Onsala, Sweden; Department of Astronomy, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Olofsson
authors.affiliation: Observatorio Astronómico Nacional (IGN), Alfonso XII N°3, E-28014 Madrid, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Planesas
authors.affiliation: European Space Astronomy Centre, ESA, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid, Spain.
authors.forename: A P
authors.initials: AP
authors.lastname: Marston
authors.affiliation: Ural Federal University, Astronomical Observatory, 620000 Ekaterinburg, Russian Federation.
authors.forename: A M
authors.initials: AM
authors.lastname: Sobolev
authors.affiliation: Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 Amsterdam, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: de Koter
authors.affiliation: Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, S-439 92 Onsala, Sweden.
authors.forename: F L
authors.initials: FL
authors.lastname: Schöier
keywords: circumstellar matter; stars: AGB; stars: carbon; stars: individual: IRC+10216