VARIATIONS ON DEBRIS DISKS: ICY PLANET FORMATION AT 30-150 AU FOR 1-3 M⊙ MAIN-SEQUENCE STARS

We describe calculations for the formation of icy planets and debris disks at 30-150 AU around 1-3 M-circle dot stars. Debris disk formation coincides with the formation of planetary systems. As protoplanets grow, they stir leftover planetesimals to large velocities. A cascade of collisions then grinds the leftovers to dust, forming an observable debris disk. Stellar lifetimes and the collisional cascade limit the growth of protoplanets. The maximum radius of icy planets, r(max) approximate to 1750 km, is remarkably independent of initial disk mass, stellar mass, and stellar age. These objects contain less than or similar to 3%-4% of the initial mass in solid material. Collisional cascades produce debris disks with maximum luminosity similar to 2 x 10(-3) times the stellar luminosity. The peak 24 mu m excess varies from similar to 1% times the stellar photospheric flux for 1M(circle dot) stars to similar to 50 times the stellar photospheric flux for 3M(circle dot) stars. The peak 70-850 mu m excesses are similar to 30-100 times the stellar photospheric flux. For all stars, the 24-160 mu m excesses rise at stellar ages of 5-20 Myr, peak at 10-50 Myr, and then decline. The decline is roughly a power law, f alpha t(-n) with n approximate to 0.6-1.0. This predicted evolution agrees with published observations of A-type and solar-type stars. The observed far-IR color evolution of A-type stars also matches model predictions.