First detection of c-C3H2 in a circumstellar disk
  We report the first detection of c-C3H2 in a circumstellar disk. The c-C3H2
J=6-5 line (217.882 GHz) is detected and imaged through Atacama Large
Millimeter Array (ALMA) Science Verification observations toward the disk
around the Herbig Ae star HD 163296 at 0.8" resolution. The emission is
consistent with that arising from a Keplerian rotating disk. Two additional
c-C3H2 transitions are also tentatively detected, bolstering the identification
of this species, but with insufficient signal-to-noise ratio to constrain the
spatial distribution. Using a previously developed model for the physical
structure of this disk, we fit a radial power-law distribution model to the
c-C3H2 6-5 emission and find that c-C3H2 is present in a ring structure from an
inner radius of about 30 AU to an outer radius of about 165 AU. The column
density is estimated to be 1e12-1e13 cm-2. The clear detection and intriguing
ring structure suggest that c-C3H2 has the potential to become a useful probe
of radiation penetration in disks.
