The long wavelength view of GG Tau A: Rocks in the Ring World
  We present the first detection of GG Tau A at centimeter-wavelengths, made
with the Arcminute Microkelvin Imager Large Array (AMI-LA) at a frequency of 16
GHz ({\lambda} = 1.8 cm). The source is detected at > 6 {\sigma}_{rms} with an
integrated flux density of S = 249+/-45 {\mu}Jy. We use these new
centimetre-wave data, in conjunction with additional measurements compiled from
the literature, to investigate the long wavelength tail of the dust emission
from this unusual proto-planetary system. We use an MCMC based method to
determine maximum likelihood parameters for a simple parametric spectral model
and consider the opacity and mass of the dust contributing to the microwave
emission. We derive a dust mass of approximately 0.1 solar masses, constrain
the dimensions of the emitting region and find that the opacity index at
{\lambda} > 7mm is less than unity, implying a contribution to the dust
population from grains exceeding 4 cm in size. We suggest that this indicates
coagulation within the GG Tau A system has proceeded to the point where dust
grains have grown to the size of small rocks with dimensions of a few
centimetres. Considering the relatively young age of the GG Tau association, in
combination with the low derived disk mass, we suggest that this system may
provide a useful test case for rapid core accretion planet formation models.
