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 m observations for a subset of two stars. None of the objects observed with IRAC possess infrared excesses at 3.68.0 m; however, seven objects observed with MIPS possess 24 and/or 70 m excesses. Four objects ( Phe, HD 92945, HD 119124, and AU Mic), with estimated ages 12200 Myr, possess strong 70 m excesses, 100% larger than their predicted photospheres, and no 24 m excesses, suggesting that the dust grains in these systems are cold. One object (HD 112429) possesses moderate 24 and 70 m excesses with a color temperature, Tgr = 100 K. Two objects (1 Lib and HD 177724) possess such strong 24 m excesses that their 12, 24, and 70 m fluxes cannot be self-consistently modeled using a modified blackbody despite a 70 m excess >2 times greater than the photosphere around 1 Lib. The strong 24 m excesses may be the result of emission in spectral features, as observed toward the Hale-Bopp star HD 69830.