Volume 521, October 2010
Herschel/HIFI: first science highlights
|Number of page(s)||5|
|Published online||01 October 2010|
Letter to the Editor
A HIFI preview of warm molecular gas around χ Cygni: first detection of H2O emission toward an S-type AGB star *
Onsala Space Observatory, Chalmers University of Technology,
Dept. Radio & Spece Science, 439 92 Onsala, Sweden e-mail: email@example.com
2 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
3 Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 Amsterdam, The Netherlands
4 University of Bonn, Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
5 European Southern Observatory, Karl Schwarzschild Str. 2, Garching bei München, Germany
6 Department of Astronomy, AlbaNova University Center, Stockholm University, 10691 Stockholm, Sweden
7 Observatorio Astronómico Nacional. Ap 112, 28803 Alcalá de Henares, Spain
8 European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
9 Observatorio Astronómico Nacional (IGN), Alfonso XII N°3, 28014 Madrid, Spain
10 CAB, INTA-CSIC, Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
11 Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
12 Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
13 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
14 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
15 Johns Hopkins University, Baltimore, MD 21218, USA
16 Joint ALMA Observatory, El Golf 40, Las Condes, Santiago, Chile
17 N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland
18 Atacama Large Millimeter/Submillimeter Array, Joint ALMA Office, Santiago, Chile
19 Experimental Physics Dept., National University of Ireland Maynooth, Co. Kildare, Ireland
20 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
21 KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
22 Northrop Grumman Aerospace Systems, 1 Space Park, Redondo Beach, CA 90278, USA
Accepted: 9 June 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 χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ 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 H2) is (1.1±0.2) × 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.
Key words: stars: AGB and post-AGB / circumstellar matter / stars: kinematics and dynamics / stars: individual: χ Cyg / stars: late-type / stars: mass-loss
© ESO, 2010
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