Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
C. Helling and J.M. Winters:
Circumstellar dust shells around long-period
variables:
IX. Molecular layers resulting from shocked carbon-rich atmospheres
Astronomy and Astrophysics 366, 229-240 (2000)
Abstract.
The existence of warm zones of an enhanced molecular content
surrounding the photospheres of AGB stars has been postulated to
explain
observed molecular absorption/emission components which are in excess
of
the results obtained from classical hydrostatic model atmospheres. We
have analyzed the chemical equilibrium molecular composition of
time-dependent models of carbon-rich circumstellar envelopes for
various
combinations of the stellar parameters and found that groups of
molecules appear to be present in different zones with temporally
varying temperature and density. The regions of enhanced
molecular abundances are situated between the stellar photosphere and
the circumstellar dust shell. In the models, these zones are produced
by the levitation of the atmospheric gas due to the dissipation of
shock
waves and/or due to radiation pressure on molecules and dust.
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