OBSERVATIONS OF DISKS AROUND BROWN DWARFS IN THE TW HYDRA ASSOCIATION WITH THE SPITZER INFRARED SPECTROGRAPH

摘要: Using SpeX at the NASA Infrared Telescope Facility and Spitzer Spectrograph, we have obtained infrared spectra from 0.7 to 40 μm for three young brown dwarfs in TW Hydra association (τ ~ 10 Myr), 2MASSW J1207334–393254, J1139511–315921, SSSPM J1102–3431. The spectral energy distribution J1139511–315921 is consistent with a stellar photosphere entire wavelength range of our data, whereas other two objects exhibit significant excess emission λ > 5μm. We are able reproduce each dwarf using models irradiated accretion disks. According model fits, both disks experienced high degree dust settling. also find that silicate 20 absent these disks, indicating grains upper disk layers grown sizes larger than ~5 μm. Both characteristics previous observations decreasing lower masses older ages. These trends suggest either (1) growth grains, perhaps planetesimal formation, occurs faster around stars or (2) radii mid-IR-emitting regions smaller stars, grow radii. Finally, note possible detection an unexplained feature near 14 disk-bearing dwarfs.