title: Millimeter-wave Observations of Protoplanetary Transition Disks

authors: Sean M. Andrews, David J. Wilner, A. Meredith Hughes

abstract: Circumstellar disks are thought to experience a rapid "transition" phase in
their evolution that can have a considerable impact on the formation and early
development of planetary systems. I will present high angular resolution (0.3"
= 20-60 AU) millimeter-wave observations from a survey of such transition disks
in nearby star-forming regions. With those data, we directly resolve
dust-depleted disk cavities on scales comparable to the extent of our Solar
System. Surprisingly, these large cavities are common, comprising at least 1 in
5 (20%) of the disks at the high end of the disk mass distribution.  Utilizing
these results, I will briefly assess the physical mechanisms proposed to
account for transition disk structures.  I will argue that neither
photoevaporation or particle growth {\it alone} can reproduce the observations.
Instead, the data are more commensurate with the substantial disk structure
perturbations expected from dynamical interactions with low-mass (planetary?)
companions.  Finally, I comment on observations of the cold gas content in
these disks and highlight some updates to our approach for modeling such data.