Characterization of the Most Luminous Star in M33: A Super Symbiotic
  Binary
  We present the first spectrum of the most luminous infrared star in M33, and
use it to demonstrate that the object is almost certainly a binary composed of
a massive O star and a dust-enshrouded Red Hypergiant. This is the most
luminous symbiotic binary ever discovered. Its radial velocity is an excellent
match to that of the hydrogen gas in the disk of M33, supporting our
interpretation that it is a very young and massive binary star.
