The Rapidly Evolving AGB Star, V Hya: ALMA finds a Multi-Ring Circus
  with High-Velocity Outflows
  We have observed the mass-losing carbon star V Hya that is apparently
transitioning from an AGB star to a bipolar planetary nebula, at an
unprecedented angular resolution of ~0".4-0".6 with the Atacama Large
Millimeter/submillimeter Wave Array (ALMA). Our 13CO and 12CO (J=3-2 and J=2-1)
images have led to the discovery of a remarkable set of six expanding rings
within a flared, warped Disk structure Undergoing Dynamical Expansion (DUDE)
that lies in the system's equatorial plane. We also find, for the first time,
several bipolar, high-velocity outflows, some of which have parabolic
morphologies, implying wide opening angles, while one (found previously) is
clumpy and highly collimated. The latter is likely associated with the
high-velocity bullet-like ejections of ionized gas from V Hya; a possible
molecular counterpart to the oldest of the 4 bullets can be seen in the 12CO
images. We find a bright, unresolved central source of continuum emission (FWHM
size <~165 au); about 40% of this emission can be produced in a standard radio
photosphere, while the remaining 60% is likely due to thermal emission from
very large (mm-sized) grains, having mass >~10^{-5} Msun. We have used a
radiative transfer model to fit the salient characteristics of the DUDE's 13CO
and 12CO emission out to a radius of 8" (3200 au) with a flared disk of mass
1.7 x 10^{-3} Msun, whose expansion velocity increases increases very rapidly
with radius inside a central region of size ~200 au, and then more slowly
outside it, from 9.5 to 11.5 km/s. The DUDE's underlying density decreases
radially, interspersed with local increases that represent the observationally
well-characterised innermost three rings.
