2.12 MICRON MOLECULAR-HYDROGEN EMISSION FROM CIRCUMSTELLAR DISKS EMBEDDED IN THE ORION NEBULA

We present narrowband images of two externally illuminated circumstell ar disks embedded in the Orion Nebula. The images were taken with came ra 2 of the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) as part of the Hubble Space Telescope Early Release Observations prog ram. Molecular hydrogen emission is confined to the silhouettes embedd ed in the objects HST 10 (182-413) and HST 17 (183-419). This emission appears to trace the surfaces of nearly edge-on circumstellar disks a nd is likely to be excited by the intense far-ultraviolet (FUV) radiat ion field produced by nearby O stars. The presence of this emission co nfirms that FUV radiation penetrates to the disk surface. The absence of H-2 emission in the region between the ionization front and the dis k surface provides evidence that this medium is predominantly atomic. Our observations constitute the first demonstration that the dense cir cumstellar disks embedded in the proplyds are predominately molecular. While the central star is marginally detected at 2.15 mu m in HST 10, the central star of HST 17 is clearly detected.