Dust grain growth in rho-Ophiuchi protoplanetary disks

TL;DR

This study uses new millimeter observations of young stellar objects in rho-Ophiuchi to demonstrate rapid grain growth to mm/cm sizes in protoplanetary disks, highlighting the need for mechanisms to slow inward particle drift.

Contribution

First detailed analysis of grain growth in rho-Ophiuchi disks using 3.3 mm data, showing rapid growth and comparing properties with Taurus-Auriga disks.

Findings

Disks show shallower mm slopes than ISM, indicating grain growth.

Grain growth to mm/cm sizes occurs quickly in these disks.

No correlation between mm slope and micron-sized grain indicators.

Abstract

We present new ATCA observations at 3.3 mm of 27 young stellar objects in the rho-Oph young cluster. 25 of these sources have been detected. We analyze the sub-millimeter and millimeter SED for a subsample of 17 isolated class II protoplanetary disks and derive constraints on the grain growth and total dust mass in the disk outer regions. All the disks in our sample show a mm slope of the SED which is significantly shallower than the one observed for the ISM at these long wavelengths. This indicates that 1) class II disks in Ophiuchus host grains grown to mm/cm-sizes in their outer regions, 2) formation of mm/cm-sized pebbles is a fast process and 3) a mechanism halting or slowing down the inward radial drift of solid particles is required to explain the data. These findings are consistent with previous results in other star forming regions. We compare the dust properties of this sample with those of a uniformly selected sample in Taurus-Auriga and find no statistical evidence of any difference in terms of grain growth between the two regions. Finally, in our sample the mm slope of the SED is not found to correlate with indicators of grain growth to micron sizes in the surface layers of the inner disk.