BROWN DWARF DISKS AT AGES OF 5-10 Myr

Abstract

We present Spitzer/IRAC and MIPS 24 mu m observations for 28 brown dwarfs in the Upper Scorpius (UppSco) region. We find a disk fraction of 10.7%-(+ 8.7%)(3.3%) . One object shows a small excess at 24 mu m but none at shorter wavelengths, and may be a candidate transition disk. Three objects show emission in the 10 mu m silicate feature and we present compositional fits for these sources. Flat structures are observed for all disk sources in UppSco. Also presented are the MIPS/70 mu m observations for the TW Hydrae Association brown dwarf 2MASS J1139511-315921. We discuss the structure and chemistry of brown dwarf disks at ages of similar to 5-10 Myr, and consider the possible effects of the brown dwarf densities in these clusters on the disk lifetimes.