The rich far-infrared water vapour spectrum of W Hya (original) (raw)

We present an ISO Long Wavelength Spectrometer (LWS) grating spectrum of the oxygen-rich AGB star W Hya from 43-197μm. The spectrum is dominated by a forest of water vapour emission lines, confirming that H_2_O molecules are the dominant coolants of the winds of these stars. We have constructed an outflow model for the H_2_O spectrum of W Hya, which successfully matches the fluxes of most of the observed H_2_O lines, using an adopted wind temperature profile. These fits are sensitive to the mass loss rate, to the H_2_O abundance and to the inner radius of the H_2_O emitting region. The best fit parameters correspond to a mass loss rate of 6x10^-7^Msun_/yr, inner and outer radii for the emitting region of 1.5x10^14^ and 1x10^16^cm, and a H_2_O/H_2_ abundance of 8x10^-4^ for r <=4.5x10^14^cm and 3x10^-4^ at large radii. A decrease of the H_2_O/H_2_ abundance in the outer envelope is consistent with the predictions of photochemical models. The availability for the first time of obse...