Helical Magnetic Fields in the NGC1333 IRAS 4A Protostellar Outflows
  We present Submillimeter Array (SMA) polarization observations of the CO $J$
= 3--2 line toward the NGC1333 IRAS 4A. The CO Stokes $I$ maps at an angular
resolution of $\sim$1$\arcsec$ reveal two bipolar outflows from the binary
sources of the NGC 1333 IRAS 4A. The kinematic features of the CO emission can
be modeled by wind-driven outflows at $\sim$ 20$\arcdeg$ inclined from the
plane of the sky. Close to the protostars the CO polarization, at an angular
resolution of $\sim$$2\farcs3$, has a position angle approximately parallel to
the magnetic field direction inferred from the dust polarizations. The CO
polarization direction appears to vary smoothly from an hourglass field around
the core to an arc-like morphology wrapping around the outflow, suggesting a
helical structure of magnetic fields that inherits the poloidal fields at the
launching point and consists of toroidal fields at a farther distance of
outflow. The helical magnetic field is consistent with the theoretical
expectations for launching and collimating outflows from a magnetized rotating
disk. Considering that the CO polarized emission is mainly contributed from the
low-velocity and low-resolution data, the helical magnetic field is likely a
product of the wind-envelope interaction in the wind-driven outflows. The CO
data reveal a PA of $\sim$ 30$\arcdeg$ deflection in the outflows. The
variation in the CO polarization angle seems to correlate with the deflections.
We speculate that the helical magnetic field contributes to $\sim$ 10$\arcdeg$
deflection of the outflows by means of Lorenz force.
