  We present the first multi-epoch N-band spectro-interferometric observations
of the carbon-rich Mira variable V Oph using MIDI at the ESO's Very Large
Telescope Interferometer. Our MIDI observations were carried out at three
different phases 0.18, 0.49, and 0.65, using three different baselines
configurations (UT2-UT4, UT1-UT4, and UT2-UT3) with projected baseline lengths
of 42-124 m. The wavelength dependence of the uniform-disk diameters obtained
at all epochs is characterized by a roughly constant region between 8 and 10
micron with a slight dip centered at ~9.5 micron and a gradual increase
longward of 10 micron. These N-band angular sizes are significantly larger than
the estimated photospheric size of V Oph. The angular sizes observed at
different epochs reveal that the object appears smaller at phase 0.49 (minimum
light) with uniform-disk diameters of ~5-12 mas than at phases 0.18 (~12-20
mas) and 0.65 (~9-15 mas). We interpret these results with a model consisting
of optically thick C2H2 layers and an optically thin dust shell. Our modeling
suggests that the C2H2 layers around V Oph are more extended (~1.7-1.8 Rstar)
at phases 0.18 and 0.65 than at phase 0.49 (~1.4 Rstar) and that the C2H2
column densities appear to be the smallest at phase 0.49. We also find that the
dust shell consists of amorphous carbon and SiC with an inner radius of ~2.5
Rstar, and the total optical depths at phases 0.18 and 0.65 are higher than
that at phase 0.49. Our MIDI observations and modeling indicate that
carbon-rich Miras also have extended layers of polyatomic molecules as
previously confirmed in oxygen-rich Miras.
