Sunday, August 30, 2015

How Large are the Dust Grains Around HL Tauri?

Grain size constraints on HL Tau with polarization signature


Kataoka et al


We report a new interpretation of the millimeter-wave polarization of the protoplanetary disk around HL Tau with self-polarization. We successfully reproduce the observed polarization signature with self-scattered light of dust grains. The detected polarization can be explained only if dust grains have a maximum size of around 150 μm. This is a strong constraint on grain size in the early stage of a circumstellar disk. The obtained grain size contradicts to previously expected grain size, which is millimeter. The inferred grain size is too small to be trapped at gas pressure bumps, and therefore it requires planet formation theory to explain the mechanism to stop the grain growth or it might suggest the dust grains are no longer spherical but highly porous.

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