Title: Millimeter Spectral Indices and Dust Trapping By Planets in Brown Dwarf Disks
Authors: Pinilla, P.; Quiroga-Nuñez, L. H.; Benisty, M.; Natta, A.; Ricci, L.; Henning, Th.; van der Plas, G.; Birnstiel, T.; Testi, L.; Ward-Duong, K.
First Author’s Institution: Department of Astronomy/Steward Observatory, The University of Arizona (USA)
Status: Published in Astrophysical Journal
ADS link: 2017ApJ...846...70P
Disks around brown dwarfs (BDs) are excellent laboratories to study the first steps of planet formation in cold and low-mass disk conditions. The radial-drift velocities of dust particles in BD disks higher than in disks around more massive stars. Therefore, BD disks are expected to be more depleted in millimeter-sized grains compared to disks around T Tauri or Herbig Ae/Be stars.
However, recent millimeter observations of BD disks revealed low millimeter spectral indices, indicating the presence of large grains in these disks and challenging models of dust evolution.
We present 3 mm photometric observations carried out with the IRAM/Plateau de Bure Interferometer (PdBI) of three BD disks in the Taurus star-forming region, which have been observed with ALMA at 0.89 mm. The disks were not resolved and only one was detected with enough confidence (∼3.5σ) with PdBI.
Based on these observations, we obtain the values and lower limits of the spectral index and find low values (α mm ≲ 3.0). We compare these observations in the context of particle trapping by an embedded planet, a promising mechanism to explain the observational signatures in more massive and warmer disks. We find, however, that this model cannot reproduce the current millimeter observations for BD disks, and multiple-strong pressure bumps globally distributed in the disk remain as a favorable scenario to explain observations. Alternative possibilities are that the gas masses in the BD disk are very low (∼2 × 10-3 M Jup) such that the millimeter grains are decoupled and do not drift, or fast growth of fluffy aggregates.