Brown Dwarfs as Exoplanet Analogs

The recent discovery of young, late-L or early-T type brown dwarfs provides a unique opportunity for detailed study of exoplanet atmospheres. These newly-discovered objects have colors, spectra and luminosities that are remarkably similar to the directly-imaged exoplanets around beta Pic, HR 8799, and 2MASS J1207. Several of these objects can be tied to local young kinematic groups, which allows a determination of age and implies planetary masses. These isolated brown dwarfs provide an interesting analog to young, dusty exoplanets in a context where detailed study of the atmospheric dust/cloud properties is possible. Using near-IR spectroscopy, we characterize the spectral type and surface gravities of these objects. We determine the effective temperatures inferred by the spectral types, atmospheric models, and luminosities of extremely red objects. At a given spectral type, we find that extremely red, young L dwarfs are cooler than field objects. The temperatures inferred by atmospheric models lead to physically implausible radii, similar to the discord seen in model atmosphere fits of young, dusty planets.