2022ApJ...941...66H

The azimuthal asymmetries of dust rings in protoplanetary disks such as a crescent around young stars are often interpreted as dust traps, and thus as ideal locations for planetesimal and planet formations. Whether such dust traps effectively promote planetesimal formation in disks around very low-mass stars (VLM; a mass of ≲0.2 M_☉) is debatable, as the dynamical and grain growth timescales in such systems are long. To investigate grain growth in such systems, we studied the dust ring with a crescent around the VLM star ZZ Tau IRS using the Karl G. Jansky Very Large Array at centimeter wavelengths. Significant signals were detected around ZZ Tau IRS. To estimate the maximum grain size (${a}_{\max }$) in the crescent, we compared the observed spectral energy distribution (SED) with SEDs for various ${a}_{\max }$ values predicted by radiative transfer calculations. We found ${a}_{\max }\,\gtrsim $ 1 mm and ≲60 μm in the crescent and ring, respectively, though our modeling efforts rely on uncertain dust properties. Our results suggest that grain growth occurred in the ZZ Tau IRS disk, relative to the sub-micron-sized interstellar medium. Planet formation in a crescent with millimeter-sized pebbles might proceed more efficiently than in other regions with submillimeter-sized pebbles via pebble accretion scenarios.