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H. B. Throop (SWRI), J. Bally (Colorado / CASA)
A significant fraction of stars forming today are born in dense OB associations such as Orion. Photo-evaporation by the UV radiation of nearby O and B stars can destroy disks around low-mass stars on 105-106 yr time-scales. Therefore, it has been suggested that the formation of planets may be difficult in OB associations.
We have developed a disk evolution model which includes photo-evaporation, grain growth, and vertical sedimentation. Solid material condenses to the midplane as in the model of Sekiya (1998). When this disk is exposed to UV radiation, the dust-depleted outer gas layers are removed, leaving behind higher concentrations of midplane dust. Continued photo-evaporation increases the gas:dust ratio until the disk mid-plane becomes gravitationally unstable according to the criteria of Youdin & Shu (2002). Gas drag no impedes rapid grain growth. Therefore, instead of preventing planetesimal formation, exposure to intense UV radiation fields may actually stimulate the rapid growth of planetesimals.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.