Paper: astro-ph/0606361
Date: Thu, 15 Jun 2006 16:58:30 GMT (324kb)

Title: Fragmentation of gravitationally unstable gaseous protoplanetary disks
with radiative transfer

Authors: Lucio Mayer (ETH Zurich), Graeme Lufkin (University of Maryland),
Thomas Quinn (University of Washington), James Wadsley (McMaster University)

Comments: 5 pages, 3 figures, submitted to ApJ Letters
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We report on the results of the first 3D SPH simulation of massive,
gravitationally unstable protoplanetary disks with radiative transfer. We adopt
a flux-limited diffusion scheme justified by the high opacity of most of the
disk. The optically thin surface of the disk cools as a blackbody. The disks
grow slowly in mass starting from a Toomre-stable initial condition to the
point at which they become marginally unstable. We find that gravitationally
bound clumps with masses close to a Jupiter mass can arise. Fragmentation
appears to be driven by vertical convective-like motions capable of
transporting the heat from the disk midplane to its surface on a timescale of
only about 40 years at 10 AU. A larger or smaller cooling efficiency of the
disk at the optically thin surface can promote or stifle fragmentation by
affecting the vertical temperature profile, which determines whether convection
can happen or not, and by regulating the accretion flow from optically thin
regions towards overdense regions. We also find that the chances of
fragmentation increase for a higher mean molecular weight $\mu$ since
compressional heating is reduced. Around a star with mass $1 M_{\odot}$ only
disks with $\mu \ge 2.4$, as expected for gas with a metallicity comparable to
solar or higher, fragment. This suggests that disk instability, like
core-accretion, should be more effective in forming gas giants at higher gas
metallicities, consistent with the observed correlation between metallicity of
the planet-hosting stars and frequency of planets

\\ ( http://arXiv.org/abs/astro-ph/0606361 , 324kb)