Dissertation
Staubbildung in Sternwinden
(Formation of Dust in Stellar Winds)
Andrea Ferrarotti
Abstract:
During the final stages of their evolution most stars become efficient
dust factories. On the Asymptotic Giant Branch (AGB) low or intermediate
mass stars loose most of their initial mass in a massive stellar wind
and develop optically very thick dust shells. Dust is very important for stellar
evolution since only dust particles cause efficient gas cooling during the
protostellar collaps. Therefore dust formation influences directly the evolution
of stars and further evolution of galaxies.
In this work condensation of dust grains were investigated under mass
loss conditions for stars with different element abundances and metallicities.
The process of dust formation for S stars were studied. It could be shown,
that FeSi, metallic iron, and small features of quartz in the infrared spectrum
of the dust shell.
Further the condensation of Fe and Mg oxide and of the solid solution
magnesiowüstite in the stellar wind of ABG giants and RGB supergiants
with oxygen rich element mixture were studied. Calculations show, that magnesiowüstite
is a likely condensate. The calculated wavelength of the
magnesiowüstite resonance corresponds to a unidentified dust feature
found in some oxygen rich circumstellar dust shells.
Finally mass loss on the AGB and dust formation rate as well as the quantities
of dust produced by evolved stars were investigated via synthetic
AGB evolutions.
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