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Astron. Astrophys. 315, L237-L240 (1996)

Detection of far-infrared rotational lines of water vapourtoward W Hydrae*

David A. Neufeld1, Wesley Chen1, Gary J. Melnick2, Thijs de Graauw3, Helmut Feuchtgruber4,5, Leo Haser5, Dieter Lutz5, and Martin Harwit6

1 Department of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
3 SRON Laboratory for Space Research, Groningen University, The Netherlands
4 ISO Science Operations Center, ESA, Villafranca, Spain
5 Max Planck Institute for Extraterrestrial Physics, D-85740 Garching, Germany
6 511 H Street, SW, Washington, DC 20024-2725, USA

Received 1 July 1996 / Accepted 20 August 1996

Abstract. We report the first detection of thermal water vapour emission from a circumstellar outflow. We have observed four far-infrared rotational emission lines of water vapour and one water absorption feature toward the evolved star W Hydrae, using the Short Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). Three of the emission lines were observed in the instrument's Fabry-Perot mode at a resolving power img1.gif of approximately 30,000: the 7 img2.gif line at 29.84 img5.gifm, the 4 img4.gif line at 31.77 img5.gifm, and the img6.gif line at 40.69 img5.gifm. One additional emission line, the img7.gif line at 37.98 img5.gifm, and one absorption feature at 38.08 img5.gif m that we attribute to a blend of the img8.gif and the img9.gif water lines were observed in grating mode at a resolving power of about 2,000. The observed emission line fluxes were img10.gif , img11.gif , img12.gif and img13.gif respectively, and the equivalent width of the absorption feature was img14.gif . To within the possible errors in the flux calibration, the observed emission line fluxes can be accounted for simultaneously by a model similar to that of Chen & Neufeld (1995), given a mass-loss rate in the range img15.gif . This range lies at least a factor img16.gif above an independent estimate of the mass-loss rate that may be derived from dynamical considerations, and at least a factor img17.gif above previous estimates based upon the interpretation of CO observations.

Key words: stars: circumstellar matter - stars: late-type - infrared: stars - molecular processes

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) and with the participation of ISAS and NASA. The SWS is a joint project of SRON and MPE.

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Last change: December 16, 1996
© European Southern Observatory (ESO) 1996