Water vapour and ammonia in circumstellar envelopes of C-rich evolved stars

Schmidt, Miroslaw R.

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https://hdl.handle.net/2142/100639 Copy

Description

Title

Water vapour and ammonia in circumstellar envelopes of C-rich evolved stars

Author(s)

Schmidt, Miroslaw R.

Issue Date

2018-06-21

Keyword(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 ν2 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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100639

DOI

10.15278/isms.2018.RI07

Copyright and License Information

Copyright 2018 Miroslaw R. Schmidt

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