The Spitzer Census of Transition Disks

First Author:
James Muzerolle
Email: jmuzerolle AT
University of Arizona, Steward Observatory
933 N Cherry Ave
Tucson, AZ 85721 USA

Spitzer is making great strides in our understanding of disk evolution. In particular, detailed studies of transition disks, protoplanetary disks with AU-scale inner "holes", are now possible, with Spitzer's sensitivity and efficient mapping providing statistically significant samples for the first time. I will present the latest results on transition disk statistics, showing trends as a function of stellar properties such as mass, age, accretion, and environment. There are significant dependences with stellar mass and age, which suggest that multiple mechanisms may be responsible for inner disk clearing. I will review the leading possibilities, including dust grain growth, viscous evolution, photoevaporation, and dynamical clearing from a binary companion or newly formed giant planet. I will also touch upon nomenclature, particularly what "transition" really means and whether it represents a universal phase of disk evolution connecting protoplanetary and debris disks. Time permitting, I will present new observations of mid-infrared variability in some transition objects and discuss implications for following changes in disk structure, possibly as a result of dynamical interactions with stellar or planetary companions.
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