http://arxiv.org/abs/1805.07348
Previous observations and ideal magneto-hydrodynamic (MHD) simulations have reported that magnetic fields aligned with the rotation axis, often the bipolar outflow direction, in the youngest protostellar systems prevent a rotationally supported disk from being formed due to efficient magnetic braking, which is known as the magnetic braking catastrophe. We carried out polarimetric observations of the Atacama Large Millimeter/submillimeter Array (ALMA) toward the youngest protostellar system L1448 IRS 2, which is a proto-binary embedded within a flattened, rotating structure, and for which a hint of a central disk has been suggested, but whose magnetic fields are aligned with the bipolar outflow. Our high sensitivity observations show a beautiful hourglass morphology of magnetic fields in the protostellar system, with a toroidal field at the center, which is strong evidence for a circumstellar disk. We have also found a relationship between polarization fractions and intensities, which has various slopes that can be understood through multiple polarization mechanisms, optical depth effects, and depolarization due to field changes. In addition, we found clumpy strips crossing the center perpendicular to the bipolar outflow. Moreover, the magnetic field strength estimated by the Davis-Chandrasekhar-Fermi method is strong enough to hinder formation of a rotationally supported disk, which is inconsistent with the central toroidal field. We conclude that in this source the magnetic braking is not so catastrophic and that non-ideal MHD effects should be considered for a better understanding of early disk and companion star formation in young stellar objects.
W. Kwon, I. Stephens, J. Tobin, et. al.
Mon, 21 May 18
38/71
Comments: 12 pages, submitted to ApJL
You must be logged in to post a comment.