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Herschel/HIFI deepens the circumstellar NH_3 enigma

Menten, K. M. and Phillips, T. G. and Morris, P. (2010) Herschel/HIFI deepens the circumstellar NH_3 enigma. Astronomy and Astrophysics, 521 . Art. No. L7. ISSN 0004-6361.

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Context. Circumstellar envelopes (CSEs) of a variety of evolved stars have been found to contain ammonia (NH_3) 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 NH_3 ortho JK = 1_0−0_0 ground-state line. Methods. We used the Heterodyne Instrument for the Far Infrared aboard Herschel to observe the NH_3 JK = 1_0−0_0 transition near 572.5 GHz, simultaneously with the ortho-H_2O 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 NH_3 abundance in these objects' CSEs. For the last two stars, Very Large Array imaging of NH_3 radio-wavelength inversion lines were used to provide further constraints, particularly on the spatial extent of the NH_3-emitting regions. Results. We find remarkably strong NH3 emission in all of our objects with the NH_3 line intensities rivaling those of the ground state H_2O line. The NH3 abundances relative to H2 are very high and range from 2 × 10^(−7) to 3 × 10^(−6) for the objects we have studied. Conclusions. Our observations confirm and even deepen the circumstellar NH_3 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 NH_3 lines and imaging with the Expanded Very Large Array.

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Additional Information:© 2010 ESO. Received 31 May 2010, Accepted 29 June 2010, Published online 01 October 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Appendix A (page 5) is only available in electronic form at HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France, and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri- INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA); Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. HCSS / HSpot / HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. This work has been partially supported by the Spanish MICINN, within the program CONSOLIDER INGENIO 2010, under grant “Molecular Astrophysics: The Herschel and ALMA Era – ASTROMOL” (ref.: CSD2009-00038). R. Sz. and M. Sch. acknowledge support from grant N 203 393334 from the Polish MNiSW. K. J. acknowledges the funding from SNSB. J. C. thanks funding from MICINN, grant AYA2009-07304.
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Ministerio de Ciencia e Innovación (MCINN) (Spain)CSD2009-00038
Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW) (Poland)N 203 393334
Swedish National Space Board (SNSB)UNSPECIFIED
Ministerio de Ciencia e Innovación (MCINN) (Spain)AYA2009-07304
Subject Keywords:stars: AGB and post-AGB – supergiants – circumstellar matter
Record Number:CaltechAUTHORS:20110103-132419076
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Official Citation:Herschel/HIFI deepens the circumstellar NH3 enigma K. M. Menten, F. Wyrowski, J. Alcolea, E. De Beck, L. Decin, A. P. Marston, V. Bujarrabal, J. Cernicharo, C. Dominik, K. Justtanont, A. de Koter, G. Melnick, D. A. Neufeld, H. Olofsson, P. Planesas, M. Schmidt, F. L. Schöier, R. Szczerba, D. Teyssier, L. B. F. M. Waters, K. Edwards, M. Olberg, T. G. Phillips, P. Morris, M. Salez and E. Caux A&A 521 L7 (2010) DOI: 10.1051/0004-6361/201015108
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21548
Deposited By: Benjamin Perez
Deposited On:03 Jan 2011 22:34
Last Modified:26 Dec 2012 12:48

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