  The disk surrounding SAO 206462, an 8 Myr-old Herbig Ae star, has recently
been reported to exhibit spiral arms, an asymmetric dust continuum, and a
dust-depleted inner cavity. By carrying out two-dimensional, two-fluid
hydrodynamic calculations, we find that a planetary-mass companion located at
the outer disk could be responsible for these observed structures. In this
model, the planet excites primary and secondary arms interior to its orbit. It
also carves a gap and generates a local pressure bump at the inner gap edge
where a vortex forms through Rossby wave instability. The vortex traps radially
drifting dust particles, forming a dust-depleted cavity in the inner disk. We
propose that the vortex is responsible for the brightest southwestern peak seen
in infrared scattered light and sub-millimeter dust continuum emission. In
particular, it is possible that the scattered light is boosted as one of the
spiral arms passes through the high density vortex region, although the vortex
alone may be able to explain the peak. We suggest that a planetary companion
with a mass of 10-15 M_J is orbiting SAO 206462 at 100-120 au. Monitoring of
the brightest peak over the next few years will help reveal its origin because
the spiral arms and vortex will show distinguishable displacement.
