Adaptive optics imaging of Vy Canis Majoris at 2-5 μm with LBT/LMIRCam

We present adaptive optics images of the extreme red supergiant VY Canis Majoris in the K_s , L′, and M bands (2.15-4.8 μm) made with LMIRCam on the Large Binocular Telescope. The peculiar "Southwest Clump" previously imaged from 1 to 2.2 μm 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 5 × 10^-3 M_⊙ to 2.5 × 10^-2 M _⊙ 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 CMa's history of asymmetric high-mass-loss events.