ADAPTIVE OPTICS OBSERVATIONS OF 3 μm WATER ICE IN SILHOUETTE DISKS IN THE ORION NEBULA CLUSTER AND M43

We present the near-infrared images and spectra of four silhouette disks in the Orion Nebula Cluster (M42) and M43 using the Subaru Adaptive Optics system. While d053-717 and d141-1952 show no water ice feature at 3.1 mu m, a moderately deep ([tau] sub(ice) ~ 0.7) water ice absorption is detected toward d132-1832 and d216-0939. Taking into account the water ice so far detected in the silhouette disks, the critical inclination angle to produce a water ice absorption feature is confirmed to be 65[degrees]-75[degrees]. As for d216-0939, the crystallized water ice profile is exactly the same as in the previous observations taken 3.63 years ago. If the water ice material is located at 30 AU, then the observations suggest it is uniform at a scale of about 3.5 AU.