Dust crystallinity in protoplanetary disks: the effect of diffusion/viscosity ratio
Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: pavyar@mpia.de
Received:
16
February
2007
Accepted:
27
May
2007
The process of turbulent radial mixing in protoplanetary disks has
strong relevance to the analysis of the spatial distribution of
crystalline dust species in disks around young stars and to studies of
the composition of meteorites and comets in our own solar system.
A debate has gone on in the recent literature on the ratio of the
effective viscosity coefficient ν (responsible for accretion)
to the turbulent diffusion coefficient D (responsible for mixing).
Numerical magneto-hydrodynamic simulations have yielded values between
(Carballido et al. 2005, MNRAS, 358, 1055)
and 
(Johansen & Klahr 2005, ApJ, 634, 1353).
Here we present two analytic arguments for the ratio 
which
are based on elegant, though strongly simplified assumptions. We argue
that whichever of these numbers comes closest to reality may be determined
observationally by using spatially resolved mid-infrared
measurements of protoplanetary disks around Herbig stars. If meridional
flows are present in the disk, then we expect less abundance of
crystalline dust in the surface layers, a prediction which can likewise
be observationally tested with mid-infrared interferometers.
Key words: accretion, accretion disks / radiative transfer / diffusion
© ESO, 2007