EPoS Contribution
EPoS Contribution
Magnetic Field Effects in the Youngest Protostars

Leslie Looney
UIUC, Urbana, US
Magnetic fields likely play an important role in the early stages of disk evolution. During disk formation, magnetic braking could limit the size of the disk R<15 AU until the late Class I stage. In this talk, we will discuss the current status of high resolution polarization observations and their possible impact on young disk formation. For example, our VLA Nascent Disk and Multiplicity Survey (VANDAM) observations at 8 mm of 94 Class 0 and Class I protostars in Perseus detected 15 candidate disks R>15 AU. In all but one of these sources with known magnetic fields, the average magnetic field direction is misaligned with the rotation axis (as traced by the outflow), suggesting that magnetic braking may be minimal and allowing disks to form early. On the other hand, the other 79 sources do not have R>15 AU disks, which could mean that magnetic fields are suppressing early disk formation. In addition, the morphology of magnetic fields on small scales directly tests theoretical models of accretion drivers since the magnetorotational instability requires predominately toroidal fields while disks winds require predominately poloidal. VANDAM polarization observations of the Class 0 protostar IRAS4A implies an inferred magnetic field with circular morphology, which is expected for a magnetized rotating disk. While there is not yet a confirmed disk in IRAS4A, our observations reveal a toroidal field that is being wrapped by a rotating disk (nearly face-on, which is still allowed by the outflow) or inner envelope. At first glance, our results seem inconsistent with the lower resolution observations of hourglass field morphology seen in the 850 micron continuum. However, as material falls from the large scale envelope to the small scale disk, the frozen-in magnetic field lines are dragged along. This transition changes the morphology so that the magnetic field mirrors the disk or inner envelope rotation.
Caption: The inferred magnetic field in IRAS4A from VLA Observations at 8mm and 1 cm wavelengths. The circular field is shown as line segments, and the continuum emission is shown by contours.
J. Tobin, Leiden, NL
E. Cox, UIUC, US
R. Harris, UIUC, US
D. Segura-Cox, UIUC, US
S. Sadavoy, MPIA, DE
Z-.Y. Li, VA, US
Key publication

Suggested Session: Magnetic Fields