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Astron. Astrophys. 334, 1016-1027 (1998)


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Water vapour in circumstellar envelopes

E. González-Alfonso 1, 2, J. Cernicharo 2, 3, J. Alcolea 2 and M.A. Orlandi 3

1 Universidad de Alcalá de Henares, Departamento de Física, Campus Universitario, E-28871 Alcalá de Henares, Madrid, Spain
2 Observatorio Astronómico Nacional (OAN), E-28800 Alcalá de Henares, Madrid, Spain
3 CSIC, IEM, Dpto. Física Molecular, Serrano 123, E-28006 Madrid, Spain

Received 30 April 1997 / Accepted 8 January 1998

Abstract

We present observations of the [FORMULA] line of p-H2 O at 183 GHz in the direction of the circumstellar envelopes of 23 O-rich evolved stars. The 183 GHz data are complemented with observations of CO [FORMULA] @ p-H2 O [FORMULA] at 325 GHz, o-H2 O [FORMULA] at 22 GHz and SiO v =1 [FORMULA] @ The line profiles of these transitions are compared and discussed in terms of the regions where they are formed. We have also made time variability studies of the 183 GHz water line. The changes of the line profile and flux from one epoch to another are small in comparison with those of the o-H2 O line at 22 GHz and the SiO v =1 [FORMULA] line as reported in the literature.

The main characteristics of the 183 GHz emission can be summarized as follows: a) the 183 GHz line is of maser nature; b) in stars with low mass loss rates ([FORMULA]) the emission peaks at a velocity similar to that of the star, whilst in stars with high [FORMULA] the emission peaks at velocities close to the terminal velocity of the envelope; c) in stars with high [FORMULA] the blue-shifted emission -relative to the stellar velocity- is often more intense than the red-shifted emission; d) the full width at zero power of the 183 GHz line relative to the terminal velocity of the envelope increases with [FORMULA] ; e) the power emitted in the line and [FORMULA] are also linearly correlated.

The latter empirical relationship is compatible with the emission of a saturated maser line and with small variations of H2 O abundance from object to object.

Key words: masers – stars: AGB – circumstellar matter – radio lines: stars

Send offprint requests to: E. González-Alfonso

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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