1.3mm polarized emission in the circumstellar disk of a massive
  protostar
  We present the first resolved observations of the 1.3mm polarized emission
from the disk-like structure surrounding the high-mass protostar Cepheus A HW2.
These CARMA data partially resolve the dust polarization, suggesting an uniform
morphology of polarization vectors with an average position angle of 57 degrees
and an average polarization fraction of 2.0%. The distribution of the
polarization vectors can be attributed to (1) the direct emission of
magnetically aligned grains of dust by a uniform magnetic field, or (2) the
pattern produced by the scattering of an inclined disk. We show that both
models can explain the observations, and perhaps a combination of the two
mechanisms produce the polarized emission. A third model including a toroidal
magnetic field does not match the observations. Assuming scattering is the
polarization mechanism, these observations suggest that during the first few
10000 years of high-mass star formation, grain sizes can grow from 1 to several
10s micron.
