Discovery of Toroidal Magnetic Fields around Protostars in NGC1333 IRAS 4A from Dust Polarization Measurements Shih-Ping Lai Institute of Astronomy, National Tsing Hua University, Taiwan, Hsinchu, Taiwan
The magnetic field in the low-mass protostellar core NGC1333 IRAS4A (hereafter IRAS4A) have an hourglass morphology in the scale of few thousands AU (Girart et al. 2006, Science). Here we further explore the magnetic field structure within the central 1000 AU region of IRAS4A with the sub-arcsecond resolution dust polarization data taken with SMA at 345 GHz. The SMA observations reveal that except for the regions perpendicular to the center of IRAS4A1, the magnetic field appears to be parallel the protostellar binary, IRAS4A1 and IRAS4A2, and perpendicular to the large scale hourglass structure. We model the observed polarization with a large-scale poloidal (hourglass-like) field and a small-scale toroidal field within central 1000 AU, and show that the toroidal component is necessary for producing the observed polarization pattern. This modified geometry is in agreement with the expectation of star formation theories with ideal MHD conditions and nonzero angular momentum.
Collaborators: Tao-Chung Ching, NTHU, Taiwan Josep Miquel Girart, CSIC-IEEC, Spain Ramprasad Rao, ASIAA, Taiwan