|Time:||Wednesday, January 24, 2018, 10:30am|
|Title:||Origins of (sub) millimeter disk polarization (informal talk)|
|Speaker:||Mr. Haifeng Yang (Univ. of Virginia)|
Polarized (sub)millimeter emission from dust grains has long been established as a reliable way to probe magnetic fields, which are known to be very important in the formation and evolution of stars and protoplanetary disks. However, the first spatially resolved polarization observations of the protoplanetary disk HL Tau revealed a dust polarization pattern that, if interpreted as originating from magnetically-aligned dust grains, yielded a completely unphysical magnetic field configuration. This result was very surprising and left us with an outstanding question: what is the origin of (sub)millimeter disk polarization? My work has centered on exploring the "self-scattering" of dust grains as a promising answer to this question, and one that has successfully explained many of ALMA disk polarization observations made to date. On the pessimistic front, this new interpretation means that it is very difficult to probe magnetic fields using only (sub)millimeter disk polarization, though we have found suggestive evidence that the old interpretation may still be relevant for some systems. On the bright side, polarization arising from self-scattering depends strongly on various properties of the observed system -- including grain size distribution, optical depth, and the thickness of the dust disks -- and thus gives us observational access to many new and important topics, such as grain growth and dust settling.