Oral Presentation

Radiative grain alignment in protoplanetary disks: Implications for polarimetric observations

Author(s): Ryo Tazaki (Kyoto university), Alexandre Lazarian (University of Wisconsin, Madison), Hideko Nomura (Tokyo Institute of Technology)

Presenter: Ryo Tazaki (Kyoto university)

We apply the theory of radiative torque (RAT) alignment for studying protoplanetary disks around a T-Tauri star and perform 3D radiative transfer calculations to provide the expected maps of polarized radiation to be compared with observations, such as ALMA. We revisit the issue of grain alignment for large grains expected in the protoplanetary disks and find that mm sized grain at midplane does not align with magnetic field as the Larmor precession timescale for such large grains gets longer than the gaseous damping timescale. Hence, for these grains the RAT theory predicts that the alignment axis is determined by the grain precession in respect to the radiative flux. As a result, we expect that the polarization in the azimuthal direction for the face-on disk. It is also shown that if dust grains have superparamagnetic inclusions, magnetic field alignment is possible for (sub)micron grains at the surface layer of disks, and this can be tested by mid-infrared polarimetric observations.