Probing Dust in the Atmosphere of Brown Dwarfs through Polarization

Abstract

The theoretical analysis and observational evidence indicate that a brown dwarf with an effective temperature greater than 1300 K would have a 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 that the polarized flux profile could be a potential diagnostic tool for the physical properties of dust grains. The degree of polarization that is 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 infrared 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 the tidal effect by the companion in a binary system ensures that the disk-integrated polarization is nonzero.