Paper: astro-ph/0508354
Date: Tue, 16 Aug 2005 13:41:20 GMT (126kb)

Title: The Effects of Metallicity and Grain Size on Gravitational Instabilities
in Protoplanetary Disks

Authors: Kai Cai, Richard H. Durisen, Scott Michael, Aaron C. Boley, Annie C.
Mej\'ia, Megan K. Pickett, Paola D'Alessio

Comments: 8 pages, 2 figures, used AASTeX, to be submitted to ApJ Letter; for
related movies, see http://westworld.astro.indiana.edu/Movies/internal/kai/
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Observational studies show that the probability of finding gas giant planets
around a star increases with the star's metallicity. Our latest simulations of
disks undergoing gravitational instabilities (GI's) with realistic radiative
cooling indicate that protoplanetary disks with lower metallicity generally
cool faster and thus show stronger overall GI-activity. Moreover, the global
cooling times in our simulations appear to be too long for disk fragmentation
to occur, and, so far, we find no evidence for formation of persistent dense
protoplanetary clumps. Our results run counter to the observed metallicity
trend for any scenario where gas giant planet formation requires strong GI's
and suggest that direct gas giant planet formation via disk instabilities is
unlikely to be the mechanism that produced most observed planets. Nevertheless,
GI's may still play an important role in a hybrid scenario, compatible with the
observed metallicity trend, where structure created by GI's accelerates planet
formation by core accretion.

\\ ( http://arXiv.org/abs/astro-ph/0508354 , 126kb)