The long-wavelength view of GG Tau A: Rocks in the ring world

Abstract

We present the first detection of GG Tau A at centimetre wavelengths, made with theArcminute Microkelvin Imager Large Array at a frequency of 16 GHz (λ = 1.8 cm). The source is detected at >6 σrms with an integrated flux density of S16 GHz = 249 ± 45 μJy. 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 protoplanetary 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 dustmass ofMd ≈0.1M⊕, constrain the dimensions of the emitting region and find that the opacity index at λ > 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 disc mass, we suggest that this system may provide a useful test case for rapid core accretion planet formation models. © 2013 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.