Herschel/HIFI deepens the circumstellar NH3 enigma
Journal article, 2010
Context. Circumstellar envelopes (CSEs) of a variety of evolved stars have been found to contain ammonia (NH3) in amounts that exceed predictions from conventional chemical models by many orders of magnitude. Aims. The observations reported here were performed in order to better constrain the NH3 abundance in the CSEs of four, quite diverse, oxygen-rich stars using the NH3 ortho J(K) = 1(0)-0(0) ground-state line. Methods. We used the Heterodyne Instrument for the Far Infrared aboard Herschel to observe the NH3 J(K) = 1(0)-0(0) transition near 572.5 GHz, simultaneously with the ortho-H2O J(Ka,Kc) = 1(1,0)-1(0,1) transition, toward VY CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE radiative transfer modeling with the goal to derive the NH3 abundance in these objects' CSEs. For the last two stars, Very Large Array imaging of NH3 radio-wavelength inversion lines were used to provide further constraints, particularly on the spatial extent of the NH3-emitting regions. Results. We find remarkably strong NH3 emission in all of our objects with the NH3 line intensities rivaling those of the ground state H2O line. The NH3 abundances relative to H-2 are very high and range from 2 x 10(-7) to 3 x 10(-6) for the objects we have studied. Conclusions. Our observations confirm and even deepen the circumstellar NH3 enigma. While our radiative transfer modeling does not yield satisfactory fits to the observed line profiles, it does lead to abundance estimates that confirm the very high values found in earlier studies. New ways to tackle this mystery will include further Herschel observations of more NH3 lines and imaging with the Expanded Very Large Array.
emission
circumstellar matter
inversion lines
vy canis majoris
stars: AGB and post-AGB
mass-loss
molecules
stars
irc+10216
interstellar ammonia
bearing
water
infrared observations
supergiants
Author
K. M. Menten
Max Planck Society
F. Wyrowski
Max Planck Society
J. Alcolea
Elvire De Beck
KU Leuven
L. Decin
University of Amsterdam
KU Leuven
A. P. Marston
European Space Astronomy Centre (ESAC)
V. Bujarrabal
J. Cernicharo
Centro de Astrobiologia (CAB)
C. Dominik
Radboud University
European Space Astronomy Centre (ESAC)
Kay Justtanont
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
A. de Koter
Sterrekundig Instituut Utrecht
European Space Astronomy Centre (ESAC)
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
D. A. Neufeld
Johns Hopkins University
Hans Olofsson
Chalmers, Earth and Space Sciences, Onsala Space Observatory
P. Planesas
Atacama Large Millimeter-submillimeter Array (ALMA)
M. Schmidt
Polish Academy of Sciences
Fredrik Schöier
Chalmers, Earth and Space Sciences, Onsala Space Observatory
R. Szczerba
Polish Academy of Sciences
D. Teyssier
European Space Astronomy Centre (ESAC)
Lbfm Waters
KU Leuven
University of Amsterdam
K. Edwards
Netherlands Institute for Space Research (SRON)
University of Waterloo
Michael Olberg
Chalmers, Earth and Space Sciences, Onsala Space Observatory
T. G. Phillips
California Institute of Technology (Caltech)
P. Morris
California Institute of Technology (Caltech)
M. Salez
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
Ecole Normale Superieure (ENS)
E. Caux
University of Toulouse
Institut National des Sciences de l'Univers
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 521 1 Article Number: L7- L7Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201015108