2025ApJ...981...12H

Grain growth in disks around young stars plays a crucial role in the formation of planets. Early grain growth has been suggested in the HH 212 protostellar disk by previous polarization observations. To confirm it and to determine the grain size, we analyze high-resolution multiband observations of the disk obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) in bands 9 (0.4 mm), 7 (0.9 mm), 6 (1.3 mm), and 3 (3 mm), as well as with the Very Large Array (VLA) in band Ka (9 mm), and we present new VLA data in bands Q (7 mm), K (1.3 cm), and X (3 cm). We adopt a parameterized flared disk model to fit the continuum maps of the disk in these bands and derive the opacities, albedos, and opacity spectral index β of the dust in the disk, taking into account the dust scattering ignored in the previous work modeling the multiband data of this source. For the VLA bands, we only include the band Q data in our modeling to avoid free-free emission contamination. The obtained opacities, albedos, and opacity spectral index β (with a value of ∼1.2) suggest that the upper limit of maximum grain size in the disk should be ∼130 μm, consistent with that implied in the previous polarization observations in band 7, supporting the grain growth in this disk. The values of the absorption opacities further highlight the need for a new dust composition model for Class 0/I disks.