  We present multi-epoch high-angular resolution observations of 22 GHz H2O
masers toward the silicate carbon star EU And to probe the spatio-kinematic
distribution of oxygen-rich material. EU And was observed at three epochs
(maximum time interval of 14 months) with the Very Long Baseline Array (VLBA).
Our VLBA observations of the 22 GHz H2O masers have revealed that the maser
spots are distributed along a straight line across ~20 mas, with a slight hint
of an S-shaped structure. The observed spectra show three prominent velocity
components at V_LSR = -42, -38, and -34 km s^-1, with the masers in SW
redshifted and those in NE blueshifted. The maser spots located in the middle
of the overall distribution correspond to the component at V_LSR = -38 km s^-1,
which approximately coincides with the systemic velocity. These observations
can be interpreted as either an emerging helical jet or a disk viewed almost
edge-on (a circumbinary or circum-companion disk). However, the outward motion
measured in the VLBA images taken 14 months apart is much smaller than that
expected from the jet scenario. Furthermore, the mid-infrared spectrum obtained
with the Spitzer Space Telescope indicates that the 10 micron silicate emission
is optically thin and the silicate grains are of sub-micron size. This lends
support to the presence of a circum-companion disk, because an optically thin
circumbinary disk consisting of such small grains would be blown away by the
intense radiation pressure of the primary (carbon-rich) star. If we assume
Keplerian rotation for the circum-companion disk, the mass of the companion is
estimated to be 0.5--0.8 M_sun. We also identify CO2 emission features at
13--16 micron in the Spitzer spectrum of EU And--the first unambiguous
detection of CO2 in silicate carbon stars.
