000002137 001__ 2137
000002137 005__ 20160706150203.0
000002137 0247_ $$2DOI$$a10.1051/0004-6361/201424298
000002137 037__ $$aASTROimport-294
000002137 100__ $$aKhouri, T.
000002137 245__ $$aThe wind of W Hydrae as seen by Herschel. II. The molecular envelope of W Hydrae
000002137 260__ $$c2014
000002137 520__ $$aContext. The evolution of low- and intermediate-mass stars on the asymptotic giant branch (AGB) is mainly controlled by the rate at which these stars lose mass in a stellar wind. Understanding the driving mechanism and strength of the stellar winds of AGB stars and the processes enriching their surfaces with products of nucleosynthesis are paramount to constraining AGB evolution and predicting the chemical evolution of galaxies.  Aims: In a previous paper we have constrained the structure of the outflowing envelope of W Hya using spectral lines of the 12CO molecule. Here we broaden this study by including an extensive set of H2O and 28SiO lines. It is the first time such a comprehensive study is performed for this source. The oxygen isotopic ratios and the 28SiO abundance profile can be connected to the initial stellar mass and to crucial aspects of dust formation at the base of the stellar wind, respectively.  Methods: We model the molecular emission observed by the three instruments on board Herschel Space Observatory using a state-of-the-art molecular excitation and radiative transfer code. We also account for the dust radiation field in our calculations.  Results: We find an H2O ortho-to-para ratio of 2.5 +2.5-1.0, consistent with what is expected for an AGB wind. The O16/O17 ratio indicates that W Hya has an initial mass of about 1.5 M?. Although the ortho- and para-H2O lines observed by HIFI appear to trace gas of slightly different physical properties, we find that a turbulence velocity of 0.7 ± 0.1 km s-1 fits the HIFI lines of both spin isomers and those of 28SiO well. Conclusions: The modelling of H2O and 28SiO confirms the properties of the envelope model of W Hya, as derived from 12CO lines, and allows us to constrain the turbulence velocity. The ortho- and para-H216O and 28SiO abundances relative to H2 are (6+ 3-2)×10-4, (3+ 2-1)×10-4, and (3.3 ± 0.8) × 10-5, respectively, in agreement with expectations for oxygen-rich AGB outflows. Assuming a solar silicon-to-carbon ratio, the 28SiO line emission model is consistent with about one-third of the silicon atoms being locked up in dust particles. Appendices are available in electronic form at http://www.aanda.org
000002137 700__ $$ade Koter, A.
000002137 700__ $$aDecin, L.
000002137 700__ $$aWaters, L. B. F. M.
000002137 700__ $$aMaercker, M.
000002137 700__ $$aLombaert, R.
000002137 700__ $$aAlcolea, J.
000002137 700__ $$aBlommaert, J. A. D. L.
000002137 700__ $$aBujarrabal, V.
000002137 700__ $$aGroenewegen, M. A. T.
000002137 700__ $$aJusttanont, K.
000002137 700__ $$aKerschbaum, F.
000002137 700__ $$aMatsuura, M.
000002137 700__ $$aMenten, K. M.
000002137 700__ $$aOlofsson, H.
000002137 700__ $$aPlanesas, P.
000002137 700__ $$aRoyer, P.
000002137 700__ $$aSchmidt, M. R.
000002137 700__ $$aSzczerba, R.
000002137 700__ $$aTeyssier, D.
000002137 700__ $$aYates, J.
000002137 773__ $$cA67$$pAstronomy and Astrophysics$$v570$$y2014
000002137 85642 $$ahttp://esoads.eso.org/abs/2014A%26A...570A..67K
000002137 905__ $$apublished in
000002137 980__ $$aREFERD