Probing Dust in the Atmosphere of Brown Dwarfs through Polarization

Theoretical analysis and observational evidences indicate that a brown dwarf with effective temperature greater than 1300 K would have dust cloud in its atmosphere. In this letter, we show that dust scattering should yield polarized continuum radiation from the relatively warm brown dwarfs and the polarized flux profile could be a potential diagnosis tool for the optical and the physical properties of dust grains. The degree of polarization due to multiple scattering will be more in the optical region if the particle size is small while significant polarization should be detected in the infra-red region if the particle size is large. It is pointed out that the departure from sphericity in the shape of the object due to rapid rotation and due to tidal effect by the companion in a binary system ensures the disc integrated polarization to be non-zero. Subject headings: radiative transfer scattering polarization stars:atmosphere stars:brown dwarfs