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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 ; Kay Justtanont (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; A. de Koter ; G. Melnick ; D. A. Neufeld ; Hans Olofsson (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; P. Planesas ; M. Schmidt ; Fredrik L. Schöier (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; R. Szczerba ; D. Teyssier ; Lbfm Waters ; K. Edwards ; Michael Olberg (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; T. G. Phillips ; P. Morris ; M. Salez ; E. Caux
Astronomy and Astrophysics (0004-6361). Vol. 521 (2010), p. Article Number: L7.
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: stars: AGB and post-AGB, supergiants, circumstellar matter, vy canis majoris, infrared observations, interstellar ammonia, bearing, molecules, inversion lines, mass-loss, irc+10216, stars, emission, water



Denna post skapades 2010-12-17. Senast ändrad 2015-06-23.
CPL Pubid: 131189

 

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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik (2010-2017)
Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium (2010-2017)

Ämnesområden

Astronomi, astrofysik och kosmologi

Chalmers infrastruktur