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Haifeng Yang (THU)
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A remote talk by the distinguished fellow
2021-01-19 13:30 - 14:30
(Sub)millimeter dust thermal emission is a traditional and successful method to study the magnetic fields on scales larger than disks. Thanks to the recent development of interferometric polarimetry, especially ALMA, we have been able to study resolved polarization image on disk scales. The results, however, have been surprising. Instead of dichroic thermal emission from grains aligned with magnetic fields, disks show mostly scattering-induced polarization pattern, especially at shorter wavelengths. In this talk, I will first discuss the feasibility of the alignment of dust grains with magnetic fields in PPDs, with the so-called superparamagnetic inclusions taken into account. I will show that large millimeter-sized dust grains can hardly be aligned with magnetic fields, due to the dense environment and frequent gas bombardment. With similar grain alignment analysis, we perform synthetic polarimetric observation using a disk formation simulation. Our results show a transition from magnetically aligned polarization to scattering-induced polarization going from the envelope scale to the disk scale. This is in agreement with a recent polarization survey in the Perseus molecular cloud. At last, I will present some preliminary results on the explanation of a non-detection of polarization from a debris disk system and discuss its implication on grain alignment theory.
