Abstract
We present the most complete picture to date of magnetic field structure around protostars on scales ~50–3,000AU with SMA dust polarization measurements obtained from all four array configurations. Our target, NGC1333 IRAS4A, is a Class 0 proto-binary system, and its magnetic field in the circumbinary envelope is consistent with an hourglass morphology on the scales of few thousand AU (Girart et al. Science 313:812–814, 2006). Here we further explore the magnetic field structure down to ~50AU with sub-arcsecond resolution SMA polarization data at 345 GHz. Our results show the magnetic field structure varies significantly at different spatial scales. At scales larger than ~1,000AU, the magnetic field again shows hourglass geometry, consistent with previous work. At the scale where the binary A1 and A2 can be resolved (<800AU), we start to see a significant magnetic field component parallel to the circumbinary envelope. We have modeled this field component and interpreted this component to be a toroidal field. This is the first ever map of toroidal fields in circumbinary envelope.