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Event Number 4807

  Thursday, April 26th, 2018

Astronomy Colloquium
Star formation, polarization, and magnetic fields in the ALMA era
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM. Talk starts at 3:45 PM
Speaker: Chat Hull, NAOJ Fellow, NAO of Japan, NAPJ Chile Observatory, Joint Alma Observatory
Abstract:
The results from the ALMA polarization system have begun both to expand and to confound our understanding of the role of the magnetic field in low-mass star formation. After a brief motivation via CARMA, SMA, and other polarization observations from the prior decade, I will discuss new ALMA results, including the highest resolution and highest sensitivity polarization images made to date of two very young, Class 0 protostellar sources. These new observations achieve ~140 AU resolution, allowing us to probe polarization -- and thus magnetic field orientation -- in the innermost regions surrounding the protostars. First is a Class 0 protostellar source in Serpens known as Ser-emb 8, where a comparison with cutting-edge, moving-mesh AREPO simulations suggests that cloud-scale turbulence -- not a large-scale magnetic field preserved from the source's natal cloud -- is dictating the magnetic field morphology immediately surrounding the protostar. In contrast, in the second source, known as Serpens SMM1, the magnetic field has clearly been shaped by the bipolar outflow emanating from the central source -- a situation that is quite different from the turbulence-dominated morphology of Ser-emb 8. Finally, I will show recent observations of polarization toward IM Lup, a much more evolved, Class II protoplanetary disk. In the case of IM Lup, consistent with previous observations of other disks, the polarization appears to be due to scattering by dust grains, thus complicating the search for magnetic fields in disks, but opening up a new window into dust grain growth and evolution.
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