Highly Ordered and Pinched Magnetic Fields in the Class 0 Protobinary System L1448 IRS 2

Woojin Kwon, Ian W. Stephens, John J. Tobin, Leslie W. Looney, Zhi Yun Li, Floris F.S. Van Der Tak, Richard M. Crutcher

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Abstract

We have carried out polarimetric observations with the Atacama Large Millimeter/submillimeter Array toward the Class 0 protostellar system L1448 IRS 2, which is a protobinary 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 on the cloud core scale. Our high-sensitivity and high-resolution (∼100 au) observations show a clear hourglass magnetic field morphology centered on the protostellar system, but the central pattern is consistent with a toroidal field indicative of a circumstellar disk; though, other interpretations are also possible, including field lines dragged by an equatorial accretion flow into a configuration parallel to the midplane. If a relatively large disk does exist, it would suggest that the magnetic braking catastrophe is averted in this system, not through a large misalignment between the magnetic and rotation axes, but rather through some other mechanisms, such as nonideal magnetohydrodynamic effects and/or turbulence. We have also found a relationship of decreasing polarization fractions with intensities and the various slopes of this relationship can be understood as multiple polarization mechanisms and/or depolarization from a changing field morphology. In addition, we found a prominent clumpy depolarization strip crossing the center perpendicular to the bipolar outflow. Moreover, a rough estimate of the magnetic field strength indicates that the field is strong enough to hinder formation of a rotationally supported disk, which is inconsistent with the feature of a central toroidal field. This also suggests that early disk formation can happen even in young stellar objects with a strong primordial magnetic field.

Original languageEnglish (US)
Article number25
JournalAstrophysical Journal
Volume879
Issue number1
DOIs
StatePublished - Jul 1 2019

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Keywords

  • Magnetic Fields
  • Stars: Formation
  • Stars: Protostars
  • Submillimeter: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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