We present deep , near-infrared images of the circumbinary disk surrounding the pre–main-sequence binary star , ( catalog GG Tau ) A , obtained with NICMOS aboard the Hubble Space Telescope .
The spatially resolved proto-planetary disk scatters \sim 1.5 % of the stellar flux , with a near-to-far side flux ratio of \sim 1.4 , independent of wavelength , and colors that are comparable to the central source ( \Delta \left ( M _ { F 110 W } - M _ { F 160 W } \right ) = 0.10 \pm 0.03 , \Delta \left ( M _ { F 160 W } - M _ { F 205 W } \right ) = -0.04 \pm 0.06 ) ; all of these properties are significantly different from the earlier ground-based observations .
New Monte Carlo scattering simulations of the disk emphasize that the general properties of the disk , such as disk flux , near side to far side flux ratio and integrated colors , can be approximately reproduced using ISM-like dust grains , without the presence of either circumstellar disks or large dust grains , as had previously been suggested .
A single parameter phase function is fitted to the observed azimuthal variation in disk flux , providing a lower limit on the median grain size of a > 0.23 µm .
Our analysis , in comparison to previous simulations , shows that the major limitation to the study of grain growth in T Tauri disk systems through scattered light lies in the uncertain ISM dust grain properties .
Without explicit determination of the scattering properties it is not possible to differentiate between geometric , scattering and evolutionary effects .
Finally , we use the 9 year baseline of astrometric measurements of the binary to solve the complete orbit , assuming that the binary is coplanar with the circumbinary ring .
We find that the estimated 1 \sigma range on disk inner edge to semi-major axis ratio , 3.2 < R _ { in } / a < 6.7 , is larger than that estimated by previous SPH simulations of binary-disk interactions .