Diploma Thesis
Staubbildung in den Hüllen um S-Sterne
Andrea Ferrarotti
Abstract:
S-stars are transition objects at the top of the AGB between M- and C-stars. The third
dredge-up in thermally pulsating AGB-stars transports newly synthesized carbon from the
He burning zone into the stellar atmosphere. If the carbon and oxygen abundance are about
equal the star is classified as being of spectral type S. Stars at the top of the AGB are
subject to large mass-loss caused by a strong stellar wind. At some distance from the star
the temperature of the gas drops below the condensation temperature of some mineral compounds
and soot. This results in optically thick dust shells which are sources of an intense
IR-radiation from warm dust. The composition of the dust formed in the stellar outflow critically
depends on the C/O-ratio. In this work we have investigated the condensation processes for the
peculiar element mixture of the M-S-C transition on the AGB. From thermodynamic equilibrium
calculations we find that the most likely solids to be formed are solid FeSi, metallic iron and
small quantities of forsterite and SiC. Nucleation of dust may be triggered by TiC, ZrC or TiO2.
For these substances, non-equlibrium dust condensation in the outflow is calculated for a simple
wind model. The results of our calculation show that dust condensates in S-Stars.
Thesis: ps.gz file (1255882 Bytes)
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