Herschel/HIFI observations of the circumstellar ammonia lines in IRC+10216
Journal article, 2016
Context. 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. Aims. To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho-and para-NH3 transitions toward IRC+10216 were obtained with Herschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3 in the envelope of IRC+10216. Methods. We used the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel to observe all rotational transitions up to the J = 3 level (three ortho-and six para-NH3 lines). 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 the nu(2) band taken from the literature. Results. We found that NIR pumping is of key importance for understanding the excitation of rotational levels of NH3. The derived NH3 abundances relative to molecular hydrogen were (2.8 +/- 0.5) x 10(-8) for ortho-NH3 and (3.2(-0.6)(+0.7)) x 10(-8) 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 NH3 inferred 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 (1 sigma confidence level).
stars: individual: IRC+10216
circumstellar matter
stars: carbon
stars: AGB and post-AGB
Author
M. Schmidt
Polish Academy of Sciences
J. H. He
Chinese Academy of Sciences
R. Szczerba
Polish Academy of Sciences
V. Bujarrabal
Spanish National Observatory (OAN)
J. Alcolea
Spanish National Observatory (OAN)
J. Cernicharo
CSIC - Instituto de Ciencia de Materiales de Madrid (ICMM)
L. Decin
University of Amsterdam
KU Leuven
Kay Justtanont
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
D. Teyssier
European Space Astronomy Centre (ESAC)
K. M. Menten
Max Planck Society
D. A. Neufeld
Johns Hopkins University
Hans Olofsson
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
P. Planesas
Spanish National Observatory (OAN)
A. P. Marston
European Space Astronomy Centre (ESAC)
A. M. Sobolev
Ural Federal University
A. de Koter
University of Amsterdam
Fredrik Schöier
Chalmers, Earth and Space Sciences, Onsala Space Observatory
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 592 A131Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201527290