The disk fractions of brown dwarfs in IC 348 and Chamaeleon I

Using the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope, we have obtained mid-infrared photometry for 25 and 18 low-mass members of the IC 348 and Chamaeleon I star-forming clusters, respectively (> M6, M less than or similar to 0.08 M-circle dot). We find that 42% +/- 13% and 50% +/- 17% of the two samples exhibit excess emission indicative of circumstellar disks. In comparison, the disk fractions for stellar members of these clusters are 33% +/- 4% and 45% +/- 7% (M0-M6, 0.7 M-circle dot greater than or similar to M greater than or similar to 0.1 M-circle dot). The similarity in the disk fractions of stars and brown dwarfs is consistent with a common formation mechanism and indicates that the raw materials for planet formation are available around brown dwarfs as often as around stars.