Sunday, August 7, 2016

Multiple gaps with large grain deficit in the protoplanetary disk around TW Hya

Multiple gaps with large grain deficit in the protoplanetary disk around TW Hya

Tsukagoshi et al


We report ∼3 au resolution imaging observations of the protoplanetary disk around TW Hya at 138 and 230 GHz with the Atacama Large Millimeter/Submillimeter Array. Our observations revealed two deep gaps (∼25--50 %) at 22 and 37 au and shallower gaps (a few %) at 6, 28, and 44 au, as recently reported by Andrews et al. (2016). The central hole with a radius of ∼3 au was also marginally resolved. The most remarkable finding is that the power-law index of the dust opacity β, derived from the spectral index α between bands 4 and 6, peaks at the 22 au gap with β∼1.7 and decreases toward the disk center to β∼0. Our model fitting suggests that the overall disk structure can be reproduced with the inner hole and the gaps at 22 and 37 au. The most prominent gap at 22~au could be caused by the gravitational interaction between the disk and an unseen planet with a mass of ≲1.5 MNeptune although other origins may be possible. The planet-induced gap is supported by the fact that β is enhanced at the 22 au gap, indicating a deficit of ∼mm-sized grains within the gap due to dust filtration by a planet. Alternatively, the destruction of large dust aggregates due to the sintering of major volatiles might cause the multiple ring structure. We also find weak sinusoidal patterns with wavelengths of 5--10 au, which may be related to dynamical instabilities within the disk.

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