A Spitzer Study of Dusty Disks around Nearby, Young Stars

We have obtained Spitzer Space Telescope MIPS (Multiband Imaging Photometer for Spitzer) observations of 39 A- through M-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 μm observations for a subset of two stars. None of the objects observed with IRAC possess infrared excesses at 3.6-8.0 μm; however, seven objects observed with MIPS possess 24 and/or 70 μm excesses. Four objects (κ Phe, HD 92945, HD 119124, and AU Mic), with estimated ages 12-200 Myr, possess strong 70 μm excesses, ≥100% larger than their predicted photospheres, and no 24 μm excesses, suggesting that the dust grains in these systems are cold. One object (HD 112429) possesses moderate 24 and 70 μm excesses with a color temperature, T_gr = 100 K. Two objects (α¹ Lib and HD 177724) possess such strong 24 μm excesses that their 12, 24, and 70 μm fluxes cannot be self-consistently modeled using a modified blackbody despite a 70 μm excess >2 times greater than the photosphere around α¹ Lib. The strong 24 μm excesses may be the result of emission in spectral features, as observed toward the Hale-Bopp star HD 69830.