A HIFI preview of warm molecular gas around chi Cygni: first detection of H2O emission toward an S-type AGB star
Artikel i vetenskaplig tidskrift, 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.

stars: mass-loss

rotational line-profiles

circumstellar matter

mass-loss rates

stars: AGB and post-AGB

circumstellar water-vapor


carbon stars

evolved stars

giant branch stars


stars: kinematics and



loss history

stars: late-type

stars: individual: chi Cyg


Kay Justtanont

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

L. Decin

Universiteit Van Amsterdam

KU Leuven

Fredrik Schöier

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

Matthias Maercker

Universität Bonn

European Southern Observatory

Hans Olofsson

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

V. Bujarrabal

Observatorio Astronomico Nacional

A. P. Marston

European Space Astronomy Centre

D. Teyssier

European Space Astronomy Centre

J. Alcolea

Observatorio Astronomico Nacional

J. Cernicharo

CSIC-INTA - Centro de Astrobiologia (CAB)

C. Dominik

Radboud University Nijmegen

Universiteit Van Amsterdam

A. de Koter

Sterrekundig Instituut Utrecht

Universiteit Van Amsterdam

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

K. Menten

Max Planck-institutet

D. A. Neufeld

Johns Hopkins University

P. Planesas

European Space Astronomy Centre

Atacama Large Millimeter-submillimeter Array

M. Schmidt

Observatorio Astronomico Nacional

R. Szczerba

Atacama Large Millimeter-submillimeter Array

R. Waters

Universiteit Van Amsterdam

KU Leuven

T. de Graauw

Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences

N. Whyborn

Atacama Large Millimeter-submillimeter Array

T. Finn

Maynooth University

F. Helmich

SRON Netherlands Institute for Space Research

O. Siebertz

Universitat zu Koln

F. Schmulling

Universitat zu Koln

V. Ossenkopf

Universitat zu Koln

R. Lai

Northrop Grumman corporation

Astronomy and Astrophysics

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

Vol. 521 Article Number: L6- L6


Astronomi, astrofysik och kosmologi