Surface brightness of brown dwarfs (BDs) is not uniform in the presence of clouds and/or spots. The surface non-uniformity poses a severe challenge in spectral modeling of BDs and directly imaged exoplanets. However, the surface non-uniformity provides a window to gain insights into the underlying physical processes taking place in BDs. To address these questions, we propose to map the surface non-uniformities of nearby BDs using the Doppler imaging technique with Keck/NIRSPEC.
As a surface feature (spot or cloud) rotates in and out of view, it subsequently blocks the blue shift and the red shift part of a rotating body, or vice versa. As a result, spectral line profile exhibits periodical red and blue shift that modulates with rotation. By monitoring spectral line profile variation, one can infer surface non-uniformity distribution. This is the underlying method for Doppler imaging.
The Doppler Imaging technique may one day be used for remote sensing of a habitable world in combination with the high dispersion coronagraphy technique.