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

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5. Summary

In this paper, we have studied the emission of p-H2 O at 183 GHz in CEs. From the spectral appearance of the emission, the observed sources were divided into three different groups. The spectra in objects belonging to Group III, which in general coincide with those with the highest [FORMULA] values, show features shifted to velocities around [FORMULA] [FORMULA] [FORMULA], whereas the absolute maximum of the emission is also shifted, in most cases, toward the blue. The blue-shift of the emission peak is also observed in the stars from the Group II. We have shown the correlation between the magnitude of this shift and the mass loss rate of the star. The full width of the emission normalized to 2 [FORMULA] and [FORMULA] are also correlated. These characteristics are readily explained in terms of the 183 GHz line originating at larger distances from the star while [FORMULA] increases. The predominance of the blue-shifted feature more intense than the red-shifted one can be explained upon the amplification of the stellar emission by the gas approaching the observer (González-Alfonso & Cernicharo, 1998).

We have also found that the integrated line intensity corrected for the distance (and hence the power emitted in the line if we assume isotropic emission) and [FORMULA] are linearly correlated. In this instance the slope of the least square fit yields a value compatible with saturated maser emission and with a similar water vapour abundance in the various objects. In a forthcoming paper (González-Alfonso & Cernicharo, 1998) we will analyze more quantitatively these relations with the use of radiative transfer models, in order to obtain an estimate of the water abundance in O-rich evolved stars.

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© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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