Department of Astronomy 2018-2019 Colloquium Series
Dr. Sarah Sadavoy, Hubble Fellow, Smithsonian Astrophysical Observatory
Title: Polarization and Protostars: Evidence of a magnetized disk around a young protostar
Abstract: Magnetic fields are expected to impact the formation of protostars and their planet-forming disks. We typically use observations of dust polarization to infer the plane-of-the-sky magnetic field, but these observations are nontrivial on the scales of protostellar disks. In particular, there are several alternative mechanisms that produce detectable dust polarization signatures in disks and previous observations appear to favor these mechanisms over magnetic fields. In this talk, I present evidence of a magnetized, Keplerian disk around VLA 1623-A using new ALMA Band 6 dust polarization observations at ~30 au resolution. VLA 1623-A is a young protostellar source with a large Keplerian disk of ~ 360 au diameter. The ALMA data show highly ordered dust polarization, with two distinct polarization structures between the inner and the outer regions of the large disk. We find that that the inner dust polarization is well matched by models of dust self-scattering, whereas the polarization in the outer regions are well fit by a flux-frozen magnetic field disk model. Thus, the VLA 1623-A Keplerian disk has evidence of magnetization due to a poloidal magnetic field aligned with the collimated bipolar outflow. As a consequence of this magnetic field, we propose that either turbulence or non-ideal MHD processes are necessary to circumvent magnetic braking and produce the disk around VLA 1623-A.
Please note: Should you require any reasonable accommodations to ensure equal access and opportunity related to this event please contact Stacy Tiburzi at 734-764-3440 or stibu@umich.edu.
Abstract: Magnetic fields are expected to impact the formation of protostars and their planet-forming disks. We typically use observations of dust polarization to infer the plane-of-the-sky magnetic field, but these observations are nontrivial on the scales of protostellar disks. In particular, there are several alternative mechanisms that produce detectable dust polarization signatures in disks and previous observations appear to favor these mechanisms over magnetic fields. In this talk, I present evidence of a magnetized, Keplerian disk around VLA 1623-A using new ALMA Band 6 dust polarization observations at ~30 au resolution. VLA 1623-A is a young protostellar source with a large Keplerian disk of ~ 360 au diameter. The ALMA data show highly ordered dust polarization, with two distinct polarization structures between the inner and the outer regions of the large disk. We find that that the inner dust polarization is well matched by models of dust self-scattering, whereas the polarization in the outer regions are well fit by a flux-frozen magnetic field disk model. Thus, the VLA 1623-A Keplerian disk has evidence of magnetization due to a poloidal magnetic field aligned with the collimated bipolar outflow. As a consequence of this magnetic field, we propose that either turbulence or non-ideal MHD processes are necessary to circumvent magnetic braking and produce the disk around VLA 1623-A.
Please note: Should you require any reasonable accommodations to ensure equal access and opportunity related to this event please contact Stacy Tiburzi at 734-764-3440 or stibu@umich.edu.
| Building: | West Hall |
|---|---|
| Event Type: | Lecture / Discussion |
| Tags: | Astronomy, Physics, Science |
| Source: | Happening @ Michigan from Department of Astronomy, Department of Physics, Michigan Institute for Research in Astrophysics |
