Radial mixing in protoplanetary accretion disks - V. Models with different element mixtures

Protoplanetary disks as birth places of planets as well as of their host stars bear different element mixtures owing to the different chemical compositions of the environments where they are born. The chemical composition affects the structure and evolution of the disks, particularly the composition and abundance of the dust. In this work we perform one-zone model calculations of vertically selfgravitating protoplanetary accretion disks with the beta-prescription for the viscosity with different element mixtures. The models consider the chemical equilibrium condensation of the most important dust species in the disk as well as annealing of interstellar silicate dust and combustion of carbon dust. Also a new inner boundary condition is introduced which avoids the unphysical decline of the surface density Sigma of the frequently adopted no-torque (Sigma = 0) condition. The main result of the model calculations is that with decreasing metallicity the disks become less opaque and hence colder as a consequence of the reduced dust-to-gas ratio. Further we give a rough estimate for the critical value of the metallicity below which the formation of terrestrial planets is inhibited.