Dissertation
2-dimensionaler Stofftransport
in protoplanetaren Akkretionsscheiben
(2-dimensional Transport of Tracers in Protoplanetary Accretion Disks)
Michael Wehrstedt
Abstract:
Crystalline silicates and aliphatic hydrocarbons in comets as well as deuterated
species in several solar system bodies indicate an extensive radial mixing
in the primordial solar nebula, i.e. the protoplanetary accretion disk of
our solar system. To study the radial transport of matter within protoplanetary
disks it is essential to resolve the vertical direction since matter is
mixed radially outward by the complex 2-dimensional flow of the disk. In
this work I perform numerical models of protoplanetary accretion disks with
radial and vertical mixing by solving a set of 2-dimensional transport-reaction
equations for different tracers self-consistently together with the set of
disk equations in the 1+1-dimensional approximation. The global velocity
field of the disk is given by an analytical approximation of the meridional
flow pattern. The meridional flow pattern in disks which was first deduced
by Urpin (1984) exhibits an inward drift in the upper layers and an outward
drift in the midplane in most parts of the disk.
The turbulent diffusity is expressed by the beta-prescription of the viscosity.
The vertical self-gravity of the disk is included within the model. Tracers
are silicate grains (forsterit, enstatit) which anneal in the warm inner
parts of the disk and carbonaceous grains which combust by surface reactions
with OH molecules. Considerable fractions of crystallized silicates and methan
as a product of carbon combustion are transported to the site of comet formation
afar from the protosun. The 2-dimensional transport of tracers in the solar
nebula therefore offers an explanation for the crystalline silicates and
methan in the comets.
Thesis: ps.gz file (751989
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