Magnetically aligned dust and SiO maser polarization in the envelope of
  the red supergiant VY CMa
  We use Atacama Large Millimeter/submillimeter Array Band 5 science
verification observations of the red supergiant VY CMa to study the
polarization of SiO thermal/masers lines and dust continuum at ~1.7 mm
wavelength. We analyse both linear and circular polarization and derive the
magnetic field strength and structure, assuming the polarization of the lines
originates from the Zeeman effect, and that of the dust originates from aligned
dust grains. We also discuss other effects that could give rise to the observed
polarization.
  We detect, for the first time, significant polarization (~3%) of the
circumstellar dust emission at millimeter wavelengths. The polarization is
uniform with an electric vector position angle of $\sim8^\circ$. Varying levels
of linear polarization are detected for the J=4-3 28SiO v=0, 1, 2, and 29SiO
v=0, 1 lines, with the strongest polarization fraction of ~30% found for the
29SiO v=1 maser. The linear polarization vectors rotate with velocity,
consistent with earlier observations. We also find significant (up to ~1%)
circular polarization in several lines, consistent with previous measurements.
We conclude that the detection is robust against calibration and regular
instrumental errors, although we cannot yet fully rule out non-standard
instrumental effects.
  Emission from magnetically aligned grains is the most likely origin of the
observed continuum polarization. This implies that the dust is embedded in a
magnetic field >13 mG. The maser line polarization traces the magnetic field
structure. The magnetic field in the gas and dust is consistent with an
approximately toroidal field configuration, but only higher angular resolution
observations will be able to reveal more detailed field structure. If the
circular polarization is due to Zeeman splitting, it indicates a magnetic field
strength of ~1-3 Gauss, consistent with previous maser observations.
