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Astron. Astrophys. 315, L241-L244 (1996)

The rich far-infrared water vapour spectrum of W Hya

M.J. Barlow1, Nguyen-Q-Rieu2, Truong-Bach2, J. Cernicharo3, E. González-Alfonso4, X.-W. Liu1, P. Cox5, R.J. Sylvester1, P.E. Clegg6, M.J. Griffin6, B.M. Swinyard7, S.J. Unger7, J.-P. Baluteau8, E. Caux9, M. Cohen10, R.J. Cohen11, R.J. Emery7, J. Fischer12, I. Furniss1, W.M. Glencross1, M.A. Greenhouse13, C. Gry8,20, M. Joubert15, T. Lim20, D. Lorenzetti14, B. Nisini16, A. Omont17, R. Orfei16, D. Péquignot18, P. Saraceno16, G. Serra9, C.J. Skinner19, H.A. Smith13, H.J. Walker7, C. Armand20, M. Burgdorf20, D. Ewart20, A. Di Giorgio20, S. Molinari20, M. Price20, S. Sidher20, D. Texier20, and N. Trams20

1 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2 Observatoire de Paris, 61 avenue de l'Observatoire, F-75014 Paris, France
3 IEM, Dpto Fisica Molecular, CSIC, Serrano 123, E-28006 Madrid, Spain, Also at OAN, Apartado 1143, E-28800 Alcalá de Henares, Spain
4 Universidad de Alcalá de Henares, Dpto Física, Campus Universitario, E-28871 Alcalá de Henares, Madrid, Spain
5 Institut d'Astrophysique Spatiale, Bât. 120, Université Paris XI, F-91405 Orsay, France
6 Department of Physics, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK
7 Space Science Department, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, UK
8 Laboratoire d'Astronomie Spatiale, CNRS, BP 8, F-13376 Marseille Cedex 12, France
9 Centre d'Etude Spatiale des Rayonnements, CESR/CNRS-UPS, BP 4346, F-31029 Toulouse Cedex, France
10 Radio Astronomy Laboratory, 601 Campbell Hall, University of California, Berkeley, CA 94720, USA
11 Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, UK
12 Naval Research Laboratory, Remote Sensing Division, 4555 Overlook Ave, SW, Washington, DC 20375, USA
13 National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA
14 Osservatorio Astronomico di Roma, I-00040 Monte Porzio, Italy
15 CNES, 2 place Maurice Quentin, F-75001 Paris, France
16 CNR-Instituto di Fisica dello Spazio Interplanetario, Casella Postale 27 I-00044 Frascati, Italy
17 Institut d'Astrophysique, 98bis boulevard Arago, F-75014 Paris, France
18 Observatoire de Paris-Meudon, F-92190 Meudon, France
19 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
20 The LWS Instrument-Dedicated Team, ISO Science Operations Centre, P.O. Box 50727, E-28080 Madrid, Spain

Received 1 August 1996 / Accepted 29 August 1996

Abstract. We present an ISO Long Wavelength Spectrometer (LWS) grating spectrum of the oxygen-rich AGB star W Hya from 43-197 img1.gifm. The spectrum is dominated by a forest of water vapour emission lines, confirming that H2O molecules are the dominant coolants of the winds of these stars. We have constructed an outflow model for the H2O spectrum of W Hya, which successfully matches the fluxes of most of the observed H2O lines, using an adopted wind temperature profile. These fits are sensitive to the mass loss rate, to the H2O abundance and to the inner radius of the H2O emitting region. The best fit parameters correspond to a mass loss rate of 6 img3.gif Mimg4.gif yr-1, inner and outer radii for the emitting region of img6.gif and img7.gifcm, and a H2O/H2 abundance of img8.gif for img9.gif cm and img10.gif at large radii. A decrease of the H2O/H2 abundance in the outer envelope is consistent with the predictions of photochemical models. The availability for the first time of observations of the line fluxes from the dominant coolant species should enable improved models of the wind temperature distribution to be produced. [1]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.

Key words: stars: general - stars: individual: W Hya - stars: mass loss - stars: AGB and post-AGB

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