ALMA observations of rho-Oph 102: grain growth and molecular gas in the disk around a young Brown Dwarf

TL;DR

This study uses ALMA observations to reveal that brown dwarf disks contain millimeter-sized grains and substantial molecular gas, challenging existing models of dust evolution in such low-density environments.

Contribution

It provides the first evidence of mm-sized grains and gas-rich disks around brown dwarfs, expanding understanding of disk composition and evolution in low-mass objects.

Findings

Detection of dust emission at 0.89 mm and 3.2 mm wavelengths.

Evidence for mm-sized grains in the outer disk regions.

Confirmation of a gas-rich disk with a mass 0.3-1% of the brown dwarf's mass.

Abstract

We present ALMA continuum and spectral line observations of the young Brown Dwarf rho-Oph 102 at about 0.89 mm and 3.2 mm. We detect dust emission from the disk at these wavelengths and derive an upper limit on the radius of the dusty disk of ~ 40 AU. The derived variation of the dust opacity with frequency in the mm provides evidence for the presence of mm-sized grains in the disk outer regions. This result demonstrates that mm-grains are found even in the low density environments of Brown Dwarf disks and challenges our current understanding of dust evolution in disks. The CO map at 345 GHz clearly reveals molecular gas emission at the location of the Brown Dwarf, indicating a gas-rich disk as typically found for disks surrounding young pre-Main Sequence stars. We derive a disk mass of ~ 0.3-1% of the mass of the central Brown Dwarf, similar to the typical values found for disks around more massive young stars.