Evidence for Grain Growth in the Protostellar Disks of Orion

Abstract

We present a Brα (λ=4.05 μm) 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 μm 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 μm, but not >>4 μm.

Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.