We present 2 - 5 micron adaptive optics (AO) imaging and polarimetry of the famous hypergiant stars IRC +10420 and VY Canis Majoris. The imaging polarimetry of IRC +10420 with MMT-Pol at 2.2 micron resolves nebular emission with intrinsic polarizatio
n of 30%, with a high surface brightness indicating optically thick scattering. The relatively uniform distribution of this polarized emission both radially and azimuthally around the star confirms previous studies that place the scattering dust largely in the plane of the sky. Using constraints on scattered light consistent with the polarimetry at 2.2 micron, extrapolation to wavelengths in the 3 - 5 micron band predicts a scattered light component significantly below the nebular flux that is observed in our LBT/LMIRCam 3 - 5 micron AO imaging. Under the assumption this excess emission is thermal, we find a color temperature of ~ 500 K is required, well in excess of the emissivity-modified equilibrium temperature for typical astrophysical dust. The nebular features of VY CMa are found to be highly polarized (up to 60%) at 1.3 micron, again with optically thick scattering required to reproduce the observed surface brightness. This stars peculiar nebular feature dubbed the Southwest Clump is clearly detected in the 3.1 micron polarimetry as well, which, unlike IRC+10420, is consistent with scattered light alone. The high intrinsic polarizations of both hypergiants nebulae are compatible with optically thick scattering for typical dust around evolved dusty stars, where the depolarizing effect of multiple scatters is mitigated by the grains low albedos.
We present adaptive optics images of the extreme red supergiant VY Canis Majoris in the Ks, L and M bands (2.15 to 4.8 micron) made with LMIRCam on the Large Binocular Telescope (LBT). The peculiar Southwest Clump previously imaged from 1 to 2.2 micr
on appears prominently in all three filters. We find its brightness is due almost entirely to scattering, with the contribution of thermal emission limited to at most 25%. We model its brightness as optically thick scattering from silicate dust grains using typical size distributions. We find a lower limit mass for this single feature of 5E-03 Msun to 2.5E-02 Msun depending on the assumed gas-to-dust ratio. The presence of the Clump as a distinct feature with no apparent counterpart on the other side of the star is suggestive of an ejection event from a localized region of the star and is consistent with VY CMas history of asymmetric high mass loss events.
