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 Title: WATER VAPOUR AND AMMONIA IN CIRCUMSTELLAR ENVELOPES OF C-RICH EVOLVED STARS Author(s): Schmidt, Miroslaw R. Subject(s): Mini-symposium: Far-Infrared Spectroscopy Abstract: HIFI survey for water vapor and ammonia in a sample of the carbon-rich Asymptotic Giant Branch (AGB) stars has shown that their presence in circumstellar envelopes is almost universal. Models for thermochemical equilibrium in the photospheres of the carbon-rich stars predict abundances of water and ammonia many orders below the observed values. Modeling of emission lines suggests, that both molecules should be formed very close to the photospheres of the central stars. The mechanism of formation of these molecules is uncertain, and the proposed hypotheses include shock chemistry, photochemistry driven by the UV radiation leaking into the inner part of clumpy envelope and formation on dust grains. We present the results of a detailed modeling of the lowest rotational transitions observed with the Herschel/HIFI instrument in the sample of C-rich AGB stars. The aim of this analysis is to constrain their abundances and, where possible, their formation radius. Excitation of both molecules is governed by the radiative pumping, mainly in their $\nu_2$ vibrational modes. Models of molecules include a large number of levels in the ground and the first excited vibrational states. Ortho and para species of both molecules are treated separately. The transitions intensities are adopted from the BYTe (Yurchenko et al. 2011) and HITRAN (Rothman et al. 2009) databases for ammonia and water, respectively. Issue Date: 06/21/18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/100639 DOI: 10.15278/isms.2018.RI07 Other Identifier(s): RI07 Date Available in IDEALS: 2018-08-172018-12-12
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