  The formation scenario of a gapped disk, i.e., transitional disk, and its
asymmetry is still under debate. Proposed scenarios such as disk-planet
interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity,
and their combinations would result in different radial distributions of the
gas and the small (sub-$\mu$m size) and large (millimeter size) dust grains as
well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging
observations and (sub-)millimeter interferometry can trace small and large dust
grains, respectively; therefore multi-wavelength observations could help
elucidate the origin of complicated structures of a disk. Here we report SMA
observations of the dust continuum at 1.3~mm and $^{12}$CO~$J=2\rightarrow1$
line emission of the pre-transitional protoplanetary disk around the solar-mass
star PDS~70. PDS~70, a weak-lined T Tauri star, exhibits a gap in the scattered
light from its disk with a radius of $\sim$65~AU at NIR wavelengths. However,
we found a larger gap in the disk with a radius of $\sim$80~AU at 1.3~mm.
Emission from all three disk components (the gas and the small and large dust
grains) in images exhibits a deficit in brightness in the central region of the
disk, in particular, the dust-disk in small and large dust grains has
asymmetric brightness. The contrast ratio of the flux density in the dust
continuum between the peak position to the opposite side of the disk reaches
1.4. We suggest the asymmetries and different gap-radii of the disk around
PDS~70 are potentially formed by several (unseen) accreting planets inducing
dust filtration.
