A HIFI preview of warm molecular gas around chi Cygni: first detection of H2O emission toward an S-type AGB star
Journal article, 2010

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.

loss history

circumstellar water-vapor

stars: AGB and post-AGB

circumstellar matter

evolved stars



rotational line-profiles

carbon stars

giant branch stars

stars: individual: chi Cyg

stars: late-type



stars: mass-loss

stars: kinematics and

mass-loss rates


Kay Justtanont

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

L. Decin

KU Leuven

University of Amsterdam

Fredrik Schöier

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Matthias Maercker

University of Bonn

European Southern Observatory (ESO)

Hans Olofsson

Chalmers, Earth and Space Sciences, Onsala Space Observatory

V. Bujarrabal

Spanish National Observatory (OAN)

A. P. Marston

European Space Astronomy Centre (ESAC)

D. Teyssier

European Space Astronomy Centre (ESAC)

J. Alcolea

Spanish National Observatory (OAN)

J. Cernicharo

Centro de Astrobiologia (CAB)

C. Dominik

Radboud University

University of Amsterdam

A. de Koter

Sterrekundig Instituut Utrecht

University of Amsterdam

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

K. Menten

Max Planck Society

D. A. Neufeld

Johns Hopkins University

P. Planesas

Atacama Large Millimeter-submillimeter Array (ALMA)

European Space Astronomy Centre (ESAC)

M. Schmidt

Spanish National Observatory (OAN)

R. Szczerba

Atacama Large Millimeter-submillimeter Array (ALMA)

R. Waters

KU Leuven

University of Amsterdam

T. de Graauw

Polish Academy of Sciences

N. Whyborn

Atacama Large Millimeter-submillimeter Array (ALMA)

T. Finn

Maynooth University

F. Helmich

Netherlands Institute for Space Research (SRON)

O. Siebertz

University of Cologne

F. Schmulling

University of Cologne

V. Ossenkopf

University of Cologne

R. Lai

Northrop Grumman corporation

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 521 1 Article Number: L6- L6

Subject Categories

Astronomy, Astrophysics and Cosmology



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