Abundant Crystalline Silicates in the Disk of a Very Low Mass Star

We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the "Cores to Disks" Spitzer Legacy Program from mid-infrared, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5-35 mu m spectrum taken with the IRS, and it shows strong 10 and 20 mu m silicate features with high feature-to-continuum ratios and clear crystalline features out to 33 mu m. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot ( similar to 300 K) dust responsible for the 10 mu m feature consists of a roughly equal mix of small ( similar to 0.1 mu m) and large ( similar to 1.5 mu m) grains, whereas the cold ( similar to 70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (>1 mu m). Since the cold dust emission arises from deeper layers in the inner (