Resolved Multifrequency Radio Observations of GG Tau

TL;DR

This study uses high-resolution multifrequency radio observations to analyze the structure, particle size distribution, and dust mass of the circumbinary ring around GG Tau A, revealing insights into dust properties and potential particle trapping mechanisms.

Contribution

First detailed multifrequency radio imaging of GG Tau's circumbinary ring, constraining dust grain sizes and mass, and proposing a particle trap formation scenario.

Findings

The circumbinary ring has a radius of 235 AU and a width of ~60 AU.

Maximum particle size in the ring is 1-10 mm.

Dust mass in the ring is estimated at 30-300 Earth masses.

Abstract

We present sub-arcsecond resolution observations of continuum emission associated with the GG Tau quadruple star system at wavelengths of 1.3, 2.8, 7.3, and 50 mm. These data confirm that the GG Tau A binary is encircled by a circumbinary ring at a radius of 235 AU with a FWHM width of ~60 AU. We find no clear evidence for a radial gradient in the spectral shape of the ring, suggesting that the particle size distribution is spatially homogeneous on angular scales of ~0.1". A central point source, likely associated with the primary component (GG Tau Aa), exhibits a composite spectrum from dust and free-free emission. Faint emission at 7.3 mm is observed toward the low-mass star GG Tau Ba, although its origin remains uncertain. Using these measurements of the resolved, multifrequency emission structure of the GG Tau A system, models of the far-infrared to radio spectrum are developed to place constraints on the grain size distribution and dust mass in the circumbinary ring. The non-negligible curvature present in the ring spectrum implies a maximum particle size of 1-10 mm, although we are unable to place strong constraints on the distribution shape. The corresponding dust mass is 30-300 M_earth, at a temperature of 20-30 K. We discuss how this significant concentration of relatively large particles in a narrow ring at a large radius might be produced in a local region of higher gas pressures (i.e., a particle "trap") located near the inner edge of the circumbinary disk.