A GAP WITH A DEFICIT OF LARGE GRAINS IN THE PROTOPLANETARY DISK AROUND TW Hya

Abstract

We report ∼3 au resolution imaging observations of the protoplanetary disk around TW Hya at 145 and 233 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 percent) at 6, 28, and 44 au, as recently reported by Andrews et al. The central hole with a radius of ∼3 au was also marginally resolved. The most remarkable finding is that the spectral index between bands 4 and 6 peaks at the 22 au gap. The derived power-law index of the dust opacity is ∼1.7 at the 22 au gap and decreases toward the disk center to ∼0. 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  M Neptune , although other origins may be possible. The planet-induced gap is supported by the fact that is enhanced at the 22 au gap, indicating a deficit of ∼millimeter-sized grains within the gap due to dust filtration by a planet.