On massive dust clumps in the envelope of the red supergiant VY Canis
  Majoris
  The envelope of the red supergiant VY CMa has long been considered an extreme
example of episodic mass loss that is possibly taking place in other cool and
massive evolved stars. Recent submm observations of the envelope revealed
massive dusty clumps within 800 mas from the star which reinforce the picture
of drastic mass-loss phenomena in VY CMa. We present new ALMA observations at
an angular resolution of 0.1" and at an unprecedented sensitivity that reveal
further details about the dusty clumps. We resolve more discrete features and
identify a submm counterpart of a more distant Clump SW known from visual
observations. The brightest clump, named C, is resolved in the observations.
Gas seen against the resolved continuum emission of clump C produces a
molecular spectrum in absorption. Except for SW Clump, no molecular emission is
found to be associated with the dusty clumps and we propose that the dusty
structures have an atypically low gas content. We attempt to reproduce the
properties of the dusty clumps through three-dimensional radiative-transfer
modeling. Although a clump configuration explaining the observations is found,
it is not unique. A very high optical depth of all clumps to the stellar
radiation make the modeling very challenging and requires unrealistically high
dust masses. It is suggested that the dusty features have substructures, e.g.
porosity, that allows deeper penetration of stellar photons within the clumps
than in a homogeneous configuration. A comparison of the estimated clumps ages
to variations in the stellar visual flux for over a century suggests that the
mechanism responsible for their formation is not uniquely manifested by
enhanced or strongly diminished visual light. The study demonstrates that the
dusty mass-loss episodes of VY CMa are indeed unparalleled among all known
non-explosive stars. The origin of these episodes remains an unsolved problem.
