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Millimeter Spectral Indices and Dust Trapping By Planets in Brown Dwarf Disks

Abstract : 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.
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Submitted on : Friday, April 8, 2022 - 9:40:51 AM
Last modification on : Saturday, April 9, 2022 - 3:42:09 AM

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P. Pinilla, L. H. Quiroga-Nuñez, M. Benisty, A. Natta, L. Ricci, et al.. Millimeter Spectral Indices and Dust Trapping By Planets in Brown Dwarf Disks. The Astrophysical Journal, 2017, 846, ⟨10.3847/1538-4357/aa816f⟩. ⟨insu-03634942⟩

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