Dust trapping accelerates the coagulation of dust particles , and thus it represents an initial step toward the formation of planetesimals .
We report H -band ( 1.6 \mu m ) linear polarimetric observations and 0.87 mm interferometric continuum observations toward a transitional disk around LkH \alpha 330 .
As results , a pair of spiral arms were detected in the H -band emission and an asymmetric ( potentially arm-like ) structure was detected in the 0.87 mm continuum emission .
We discuss the origin of the spiral arm and the asymmetric structure , and suggest that a massive unseen planet is the most plausible explanation .
The possibility of dust trapping and grain growth causing the asymmetric structure was also investigated through the opacity index ( \beta ) by plotting the observed SED slope between 0.87 mm from our SMA observation and 1.3 mm from literature .
The results imply that grains are indistinguishable from ISM-like dust in the east side ( \beta = 2.0 \pm 0.5 ) , but much smaller in the west side \beta = 0.7 ^ { +0.5 } _ { -0.4 } , indicating differential dust size distribution between the two sides of the disk .
Combining the results of near-infrared and submillimeter observations , we conjecture that the spiral arms exist at the upper surface and an asymmetric structure resides in the disk interior .
Future observations at centimeter wavelengths and differential polarization imaging in other bands ( Y to K ) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disk .