HIGH-RESOLUTION NEAR-INFRARED IMAGING OF THE ORION-114-426 SILHOUETTEDISK

We present the first high-resolution near-infrared images of the edge- on silhouette circumstellar disk, Orion 114-426, made using NICMOS on the Hubble Space Telescope. Images taken against the bright nebular ba ckground of the ionized hydrogen Pa alpha line at 1.87 mu m show the m ajor axis of the disk to be approximately 20% smaller than at 0.6 mu m , from which we deduce the structure of the edge of the disk. Continuu m images of diffuse polar lobes above and below the plane of the disk show a morphology and evolution with wavelength consistent with predic tions for reflection nebulae in a diffuse envelope with large polar ca vities, surrounding a thin, massless, Keplerian disk, centered on an o therwise hidden central star. We make use of our observations and reas onable assumptions about the underlying disk structure to show that th e disk mass is at least 10 M+ and plausibly greater than or equal to 5 x 10(-4) M-..