Substructure Formation in a Protostellar Disk of L1527 IRS
  We analyze multi-frequency, high-resolution continuum data obtained by ALMA
and JVLA to study detailed structure of the dust distribution in the infant
disk of a Class~0/I source, L1527 IRS. We find three clumps aligning in the
north-south direction in the $7 {\rm \,mm}$ radio continuum image. The three
clumps remain even after subtracting free-free contamination, which is
estimated from the $1.3{\rm \,cm}$ continuum observations. The northern and
southern clumps are located at a distance of $\sim 15{\rm \,au}$ from the
central clump and are likely optically thick at $7{\rm \,mm}$ wavelength. The
clumps have similar integrated intensities. The symmetric physical properties
could be realized when a dust ring or spiral arms around the central protostar
is projected to the plane of the sky. We demonstrates for the first time that
such substructure may form even in the disk-forming stage, where the
surrounding materials actively accrete toward a disk-protostar system.
