Circumbinary Ring, Circumstellar disks and accretion in the binary
  system UY Aurigae
  Recent exo-planetary surveys reveal that planets can orbit and survive around
binary stars. This suggests that some fraction of young binary systems which
possess massive circumbinary disks (CB) may be in the midst of planet
formation. However, there are very few CB disks detected. We revisit one of the
known CB disks, the UY Aurigae system, and probe 13CO 2-1, C18O 2-1, SO
5(6)-4(5) and 12CO 3-2 line emission and the thermal dust continuum. Our new
results confirm the existence of the CB disk. In addition, the circumstellar
(CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral
indices between the wavelengths of 0.85 mm and 6 cm are found to be
surprisingly low, being 1.6 for both CS disks. The deprojected separation of
the binary is 1.26" based on our 1.4 mm continuum data. This is 0.07" (10 AU)
larger than in earlier studies. Combining the fact of the variation of UY Aur B
in $R$ band, we propose that the CS disk of an undetected companion UY Aur Bb
obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is
observed due to a mixing of Keplerian rotation of the CB disk, the infall and
outflow gas. The streaming gas accreting from the CB ring toward the CS disks
and possible outflows are also identified and resolved. The SO emission is
found to be at the bases of the streaming shocks. Our results suggest that the
UY Aur system is undergoing an active accretion phase from the CB disk to the
CS disks. The UY Aur B might also be a binary system, making the UY Aur a
triple system.
