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Dust trapping accelerates the coagulation of dust particles, and thus itrepresents an initial step toward the formation of planetesimals. We report$H$-band (1.6 um) linear polarimetric observations and 0.87 mm interferometriccontinuum observations toward a transitional disk around LkHa 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 continuumemission. We discuss the origin of the spiral arm and the asymmetric structure,and suggest that a massive unseen planet is the most plausible explanation. Thepossibility of dust trapping and grain growth causing the asymmetric structurewas also investigated through the opacity index (beta) by plotting the observedSED 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 theeast 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 thetwo sides of the disk. Combining the results of near-infrared and submillimeterobservations, we conjecture that the spiral arms exist at the upper surface andan asymmetric structure resides in the disk interior. Future observations atcentimeter wavelengths and differential polarization imaging in other bands (Yto K) with extreme AO imagers are required to understand how large dust grainsform and to further explore the dust distribution in the disk.

Spiral Structure and Differential Dust Size Distribution in the LkHa 330 Disk