Gijs D. Mulders, Carsten Dominik
Dust settling and grain growth are the first steps in the planet-formation
process in protoplanetary disks. These disks are observed around stars with
different spectral types, and there are indications that the disks around lower
mass stars are significantly flatter, which could indicate that they settle and
evolve faster, or in a different way.
We aim to test this assumption by modeling the median spectral energy
distributions (SEDs) of three samples of protoplanetary disks: around Herbig
stars, T Tauri stars and brown dwarfs. We focus on the turbulent mixing
strength to avoid a strong observational bias from disk and stellar properties
that depend on stellar mass.
We generated SEDs with the radiative transfer code MCMax, using a hydrostatic
disk structure and settling the dust in a self-consistent way with the
alpha-prescription to probe the turbulent mixing strength.
We are able to fit all three samples with a disk with the same input
parameters, scaling the inner edge to the dust evaporation radius and disk mass
to millimeter photometry. The Herbig stars require a special treatment for the
inner rim regions, while the T-Tauri stars require viscous heating, and the
brown dwarfs lack a good estimate of the disk mass because only few millimeter
detections exist.
We find that the turbulent mixing strength does not vary across the stellar
mass range for a fixed grain size distribution and gas-to-dust ratio. Regions
with the same temperature have a self-similar vertical structure independent of
stellar mass, but regions at the same distance from the central star appear
more settled in disks around lower mass stars. We find a relatively low
turbulent mixing strength of alpha = 10^(-4) for a standard grain size
distribution, but our results are also consistent with alpha = 0.01 for a grain
size distribution with fewer small grains or a lower gas-to-dust ratio.
View original:
http://arxiv.org/abs/1201.1453
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