  We present observations of the 51 Ophiuchi circumstellar disk made with the
Keck interferometer operating in nulling mode at N-band. We model these data
simultaneously with VLTI-MIDI visibility data and a Spitzer IRS spectrum using
a variety of optically-thin dust cloud models and an edge-on optically-thick
disk model. We find that single-component optically-thin disk models and
optically-thick disk models are inadequate to reproduce the observations, but
an optically-thin two-component disk model can reproduce all of the major
spectral and interferometric features. Our preferred disk model consists of an
inner disk of blackbody grains extending to ~4 AU and an outer disk of small
silicate grains extending out to ~1200 AU. Our model is consistent with an
inner "birth" disk of continually colliding parent bodies producing an extended
envelope of ejected small grains. This picture resembles the disks around Vega,
AU Microscopii, and Beta Pictoris, supporting the idea that 51 Ophiuchius may
be a Beta Pictoris analog.
