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A HIFI preview of warm molecular gas around chi Cygni: first detection of H2O emission toward an S-type AGB star

Kay Justtanont (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; L. Decin ; Fredrik L. Schöier (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; Matthias Maercker ; Hans Olofsson (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; V. Bujarrabal ; A. P. Marston ; D. Teyssier ; J. Alcolea ; J. Cernicharo ; C. Dominik ; A. de Koter ; G. Melnick ; K. Menten ; D. Neufeld ; P. Planesas ; M. Schmidt ; R. Szczerba ; R. Waters ; T. de Graauw ; N. Whyborn ; T. Finn ; F. Helmich ; O. Siebertz ; F. Schmulling ; V. Ossenkopf ; R. Lai
Astronomy and Astrophysics (0004-6361). Vol. 521 (2010), p. Article Number: L6.
[Artikel, refereegranskad vetenskaplig]

Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the S-type AGB star chi Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency data, make it posible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of chi Cyg. Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been performed to derive the temperature, density, and velocity structure of the circumstellar envelope. Results. We report the first detection of circumstellar H2O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters for the circumstellar envelope, we modelled both the ortho-and para-H2O lines. Our modelling results are consistent with the velocity structure expected for a dust-driven wind. The derived total H2O abundance (relative to H-2) is (1.1 +/- 0.2) x 10(-5), much lower than that in O-rich stars. The derived ortho-to-para ratio of 2.1 +/- 0.6 is close to the high-temperature equilibrium limit, consistent with H2O being formed in the photosphere.

Nyckelord: stars: AGB and post-AGB, circumstellar matter, stars: kinematics and, dynamics, stars: individual: chi Cyg, stars: late-type, stars: mass-loss, giant branch stars, mass-loss rates, circumstellar water-vapor, rotational line-profiles, evolved stars, carbon stars, loss history, w-hydrae, iso-sws, co



Denna post skapades 2010-12-17. Senast ändrad 2015-06-23.
CPL Pubid: 131160

 

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