Spectro-Polarimetry of Brown Dwarfs

Artist's rendition of cloud band structures detected on Luhman 16A, the second component of close-by binary brown dwarf system (Luhman 16B) is seen in the background). This detection was enabled using a technique called polarimetry.

Understanding clouds and weather in exoplanet and brown dwarf atmospheres is one of the most active and fascinating areas of research in the fast-moving field of extra-solar planetary system science. The stakes are high for two main reasons: clouds represent a crucial element of exoplanets and brown dwarf atmosphere dynamics, but they can also form a veil preventing us from remote sensing molecular species deeper in the atmosphere. Emitted light from cloudy exoplanet atmospheres can be highly polarized, while starlight itself is virtually unpolarized. When two images taken with orthogonal polarization filters are subtracted, unpolarized starlight is removed, revealing the polarized astrophysical signal, and providing a significant contrast gain. Polarimetry is still largely unexploited despite its information-rich content. Indeed, the direction and amplitude of the emergent polarization signal as a function of color and time enable detailed characterization of the composition, morphology, and dynamics of the scattering clouds.