(Proposal ID) S15B-002 (PI) Hashimoto, Jun (Proposal Title) Is the Multi-Ring Disk of HL Tau Excited by Planet(s) ? (Abstract) The 1.3~mm dust continuum image of HL~Tau made public by ALMA in November 2014 has surprised astronomers especially in the research field of the protoplanetary disk because a multi-ring structure was clearly detected in the HL~Tau's disk. Although the mechanism ultimately responsible for the multi-ring disk remains unclear, disk-planet interaction potentially opening a gap in a disk may create such structures. Here, I propose angular-differential- imaging (ADI) observations of HL~Tau with IRCS+LGSAO in the L' band (3.8~mu m). My ultimate goal is to detect any planetary mass companions present in the gap to test the hypothesis that disk-planet interaction creates the multi-ring structures in the disk around HL~Tau. If young planets have already formed in such a very young HL~Tau system, it will challenge and revolutionize the current theory of planet formation. Thereby, identifying and characterizing any planets present in the gap around HL~Tau is clearly important to understand planet formation. If I detect planetary mass companions, the multi-ring disk could be formed by disk-planet interactions; conversely, if I fail, other mechanisms such as a secular gravitational instability might be responsible for the multi-ring structures.