ALMA Band 3 observations of PDS 70 reveal asymmetric dust accumulation outside the planets

Kiyoaki Doi  (NAOJ/SOKENDAI)

PDS 70 is a unique target due to the two planets within the disc, making it an ideal candidate for studying the effect of planets on dust accumulation, growth, and planet formation.

Here, we present high-resolution (0.07 arcsec=10 au) dust continuum observations of PDS 70 in ALMA Band 3 (3.0 mm). Contrary to the almost symmetric dust ring observed in Band 7, our Band 3 observations revealed distinct asymmetry in the northwest direction, where the intensity is 2.5 times larger than the other directions. The difference indicates that the ring is optically thick in Band 7, suggesting the necessity of long wavelength observations to characterize the dust properties. The spectral index between Band 3 and 7 at the asymmetric peak is alpha~2.2, indicating that the region is optically thick even in Band 3, suggesting a substantial dust mass. These observations show that the planets accumulate dust grains both radially and azimuthally outside the planets and make suitable conditions for dust growth and planet formation.