Can Photoevaporation Trigger Planetesimal Formation?

We propose that UV radiation can stimulate the formation of planetesimals inexternally-illuminated protoplanetary disks. We present a numerical model ofdisk evolution including vertical sedimentation and photo-evaporation by anexternal O or B star. As solid material grows and settles toward the diskmidplane, the outer layers of the disk become dust depleted. When such a diskis exposed to UV radiation, heating drives photo-evaporative mass-loss from itssurface, generating a dust-depleted outflow. The dust:gas surface density ratioin the disk interior grows until dust in the disk midplane becomesgravitationally unstable. Thus, UV radiation fields may induce the rapidformation of planetesimals in disks where sedimentation has occurred.Comment: 4 pages, 1 figure. Revised and accepted by ApJ