Evidence for grain growth in the protostellar disks of Orion

We present a Bralpha (lambda = 4.05 mum) image of the largest silhouette proplyd in Orion (114-426) using the facility near-IR spectrometer NIRSPEC at the Keck Observatory. This is the longest wavelength observation of a silhouette disk to date. The diameter of the disk at 4 mum is only marginally smaller than that observed in the optical with the Hubble Space Telescope. This may be the first signature of chromatic extinction for the translucent outer edges of the disk, suggesting that the near- IR opacity is dominated by processed grains with typical sizes greater than 1.9 mum, but not >>4 mum.