Polarimetry for the Disks around Young Brown Dwarfs

We report the near-infrared (NIR) polarimetry of 34 young brown dwarfs (YBDs). This is the first NIR linear polarization survey for YBDs in the Taurus, rho Ophiuchi, and Chamaeleon dark clouds. The observations were conducted with SIRPOL on the IRSF 1.4-m telescope in South Africa. SIRPOL is a polarimeter which has the capability to conduct the JHKs simultaneous imaging polarimetry. Our targets are inferred to have circumstellar disks based on optical and NIR spectroscopy and their spectral energy distribution (SED). The spectral types of these targets range from M6.25 to M9.5 and the masses range from about 80 to 10 M-Jupiter. We have detected significant linear polarization from 16 YBDs. In previous studies for YBD disks, the observed SEDs have been well fit by the flat or flared disk models, thus we consider significant polarization of three YBDs is due to photon scattering by the dust in circumstellar disks rather than in envelopes. Highly polarized sources serve as 'direct' evidence for possible disk systems, and thus, YBDs with significant intrinsic polarization are best targets for future high-resolution telescopes.