Volume 521, October 2010
Herschel/HIFI: first science highlights
|Number of page(s)||4|
|Published online||01 October 2010|
Letter to the Editor
Discovery of water vapour in the carbon star V Cygni from observations with Herschel/HIFI*
The Johns Hopkins University, 3400 North Charles St, Baltimore, MD 21218, USA e-mail: email@example.com
2 Departamento de Física, Universidad de Alcalá de Henares, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
3 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
4 N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland
5 Observatorio Astronómico Nacional (IGN), Ap 112, 28803 Alcalá de Henares, Spain
6 Observatorio Astronómico Nacional (IGN), Alfonso XII No. 3, 28014 Madrid, Spain
7 CAB, INTA-CSIC, Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
8 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
9 Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 Amsterdam, The Netherlands
10 Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
11 Onsala Space Observatory, Dept. of Radio and Space Science, Chalmers University of Technology, 43992 Onsala, Sweden
12 Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
13 European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
14 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
15 Department of Astronomy, AlbaNova University Center, Stockholm University, 10691 Stockholm, Sweden
16 Joint ALMA Observatory, El Golf 40, Las Condes, Santiago, Chile
17 University of Waterloo, and University of Western Ontario, Canada
18 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
19 Atacama Large Millimeter/Submillimeter Array, Joint ALMA Office, Santiago, Chile
20 KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
Accepted: 6 July 2010
We report the discovery of water vapour toward the carbon star V Cygni. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 111–000 para-water transition at 1113.3430 GHz in the upper sideband of the Band 4b receiver. The observed spectral line profile is nearly parabolic, but with a slight asymmetry associated with blueshifted absorption, and the integrated antenna temperature is 1.69 ± 0.17 K km s-1. This detection of thermal water vapour emission, carried out as part of a small survey of water in carbon-rich stars, is only the second such detection toward a carbon-rich AGB star, the first having been obtained by the Submillimeter Wave Astronomy Satellite toward IRC+10216. For an assumed ortho-to-para ratio of 3 for water, the observed line intensity implies a water outflow rate ~3–6 × 10-5 Earth masses per year and a water abundance relative to H2 of ~2–5 × 10-6. This value is a factor of at least 104 larger than the expected photospheric abundance in a carbon-rich environment, and – as in IRC+10216 – raises the intriguing possibility that the observed water is produced by the vapourisation of orbiting comets or dwarf planets. However, observations of the single line observed to date do not permit us to place strong constraints upon the spatial distribution or origin of the observed water, but future observations of additional transitions will allow us to determine the inner radius of the H2O-emitting zone, and the H2O ortho-to-para ratio, and thereby to place important constraints upon the origin of the observed water emission.
Key words: stars: AGB and post-AGB / circumstellar matter / submillimeter: stars
© ESO, 2010
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