The long wavelength view of GG Tau A: Rocks in the Ring World

TL;DR

This study detects centimeter-wavelength emission from GG Tau A, revealing large dust grains up to centimeters in size, which suggests advanced coagulation and rapid planet formation in this young proto-planetary system.

Contribution

First detection of GG Tau A at 16 GHz, providing new insights into dust grain sizes and coagulation in a proto-planetary disk using a novel MCMC spectral modeling approach.

Findings

Dust grains have grown to centimeter sizes.

Dust opacity index is less than unity.

Estimated dust mass is approximately 0.1 solar masses.

Abstract

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.