A Spitzer study of dusty disks around nearby, young stars

We have obtained Spitzer Space Telescope MIPS (Multiband Imaging Photometer for Spitzer) observations of 39A-throughM-type dwarfs, with estimated ages between 12 and 600 Myr; IRAC observations for a subset of 11 stars; and follow-up CSO SHARC II 350 mu m observations for a subset of two stars. None of the objects observed with IRAC possess infrared excesses at 3.6 - 8.0 mu m; however, seven objects observed with MIPS possess 24 and/or 70 mu m excesses. Four objects ( k Phe, HD 92945, HD 119124, and AU Mic), with estimated ages 12 - 200 Myr, possess strong 70 mu m excesses, >= 100% larger than their predicted photospheres, and no 24 mu m excesses, suggesting that the dust grains in these systems are cold. One object ( HD 112429) possesses moderate 24 and 70 mu m excesses with a color temperature, T-gr = 100K. Two objects (alpha(1)Lib and HD 177724) possess such strong 24 mu m excesses that their 12, 24, and 70 mu m fluxes cannot be self-consistently modeled using a modified blackbody despite a 70 mu m excess > 2 times greater than the photosphere around alpha(1)Lib. The strong 24 mu m excesses may be the result of emission in spectral features, as observed toward the Hale-Bopp star HD 69830.