Oral Presentation

ALMA observations of compact dust disks stagnating at an innermost region of transitional disks

Author(s): Ryuta Orihara (Ibaraki University), Munetake Momose (Ibaraki University)

Presenter: Ryuta Orihara (Ibaraki University)

Protoplanetary disks are composed of gas and dust around young stars. Among them, disks with a depletion of dust close to the central star have been identified and are called transitional disks. Recent high-resolution imaging observations with ALMA have detected compact dust disk with a size of a few au that are stagnant in the innermost region of the transitional disk. The existence of compact dust disks is mysterious, because dust in a typical viscous accretion disk immediately falls to the parent star.
The compact disks formed also affect subsequent disk formation. A velocity information from molecular line emissions such as CO show that the rotation axis of the compact disk is tilted with respect to one of the outer disk. This tilted compact disk may absorb a light of the central star in only certain directions, making non-axisymmetry in the intensity distribution.
We observed the transitional disk around SY Cha (distance: 180.7 pc) with a spatial resolution of 7 au and detected the compact dust disk, but could not obtain sufficient resolution to understand its stracture. We constructed a model assuming the inner diameter of the compact disk to be 1 au and performed a mock observation at a wavelength of 0.44 mm, which resulted in a spatial resolution of 2 au and the detection of two intensity peaks coming from the ring structure. The detailed spatial distribution of compact dust disks obtained by such high-resolution observations is expected to provide constraints on dust retention mechanisms.
It is important to elucidate the formation mechanism of compact dust disks with a size of a few au and its impact on the subsequent disk evolution in order to understand the evolutionary process of planets. In this presentation, we review the observations of compact dust disks to date and discuss future plans for high-resolution observations based on the evolutionary process.