Abstract
We are carrying out a study of disk populations in young stellar regions spanning an age range from few Myr to ∼10 Myr. Using the unprecedented sensitivity and spatial resolution provided by the Spitzer Space Telescope with its instruments IRAC and MIPS, we have identified and characterized protoplanetary disks around young stellar objects (spanning a wide range of stellar masses) in several stellar groups. We find that for stellar groups of ∼5 Myr or older the disk frequency in intermediate mass stars (with spectral types from late B to early F) is higher than for low mass stars (with spectral types K and M). This is in contradiction with the observed trend for primordial disks evolution, in which stars with higher stellar masses dissipate their primordial disks faster. At 3 Myr the disk frequency in intermediate mass stars is still lower than for low mass stars indicating that second generation dusty disks start to dominate the disk population at 5 Myr for intermediate mass stars. This result agrees with models of evolution of solids in the region of the disk where icy object form, which suggest that at 5-10 Myr collisions start to produce large amount of dust during the transition from runaway to oligarchic growth and then dust production peaks at 10-20 Myr, when objects reach their maximum sizes.
