Structural evolution of protoplanetary disks

The collapse of rotating molecular cloud cores leads to the formation of massive accretion disks that evolve to more tenuous protoplanetary disks. Disk evolution is driven by a combination of viscous evolution, grain coagulation, photoevaporation, and accretion to the star. The pace of disk evolution can vary substantially, but massive accretion disks are thought to be typical for stars with ages 1 Myr and lower-mass protoplanetary disks with reduced or no accretion rates are usually 1-8 Myr old. Disks older than 10 Myr are almost exclusively non-accreting debris disks (see Figs. 1.3 and 1.5). 

The fundamental initial parameters of protoplanetary disk evolution are the masses and sizes of the disks. Optical silhouettes of disks in the Orion Nebula Cluster (McCaughrean O Dell 1996), scattered light imagery (e.g. Grady et al. 1999), interferometric maps in millimeter continuum or line emission (e.g. Rodmann et al. 2006 Dutrey et al. 2007), and disk spectral energy distributions 

The thermal structure of the disks plays a central role in determining the chemistry and the observable spectrum. The thermal structure, in turn, is set by the disk geometry and accretion rate, an important heat source. As a function of these parameters the mid-plane temperature of the disk can vary between the mild T r 1//2 for a flared disk to the rapidly declining of T r 3/4 for a flat disk. The highest temperatures in the static disk are reached at its innermost edge, directly exposed to the star. 

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