Astrophys. J., 846, 70-70 (2017/September-1)
Millimeter spectral indices and dust trapping by planets in brown dwarf disks.
PINILLA P., QUIROGA-NUNEZ L.H., BENISTY M., NATTA A., RICCI L., HENNING T., VAN DER PLAS G., BIRNSTIEL T., TESTI L. and WARD-DUONG K.
Abstract (from CDS):
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 (αmm <= 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 x 10–3 MJup) such that the millimeter grains are decoupled and do not drift, or fast growth of fluffy aggregates.
© 2017. The American Astronomical Society. All rights reserved.
brown dwarfs - circumstellar matter - planets and satellites: formation - protoplanetary disks - protoplanetary disks
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