RESOLVED MULTIFREQUENCY RADIO OBSERVATIONS OF GG Tau

Abstract

We present subarcsecond 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 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 ⊕ , 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.

Possible planet formation in the young, low-mass, multiple stellar system GG Tau A

“…We found a value for the spectral index β = 1.0 ± 0.1, which indicates moderate grain growth compared to interstellar dust. Such a grain growth is compatible with a recent analysis of the dust ring performed between 7 and 1.3mm 9 . We found a marginal dependency of β with radius, suggesting that larger dust particles reside near the inner edge of the outer disc (i.e.…”

“…A circumbinary disc was discovered around the young low-mass binary system GGTau-A 7 , which has recently been proven to be a hierarchical triple system 8 . It has one large inner disc 9 around the southern single star and shows small amounts of shocked H 2 gas residing within the central cavity 10 , but other than a weak detection 11 , hitherto the distribution of cold gas in this cavity or in any other binary or multiple star system has never been determined. Here we report imaging of massive CO-emitting gas fragments within the GG Tau-A cavity.…”

“…The continuum image shows cold dust emission from only one circumstellar disc-like structure associated with GGTau-Aa 9,15 . We estimate the minimum dust disc size to be ∼ 7 au while the minimum mass of gas and dust is roughly 10 −3 M ⊙ about Jupiter's mass.…”

“…Such a simple model is valid for the dust distribution since the emission is known to be confined in a ring with sharp edges 9,21 . The derived geometrical parameters are in very good agreement with the previous results 21 .…”

“…closer to the central stars), as observed for some circumstellar discs orbiting young single stars 38 . So far, dust temperatures were derived either from Monte-Carlo dust disc models 39 or one-dimensional thermal models associated to pure mm data 9 . In our case, we are able to directly derive the dust temperature thanks to the deviation from the Rayleigh Jeans regime at 0.45 mm, combined with sufficiently high spatial resolution at 0.45 mm and 1.3 mm.…”