Program: GN-2017B-Q-56

We propose high-dispersion near-infrared spectroscopy to measure the projected rotational velocities and spin axis orientations of eight L and T dwarfs with accurately known photometric periods. Given degenerate equations of state, brown dwarfs attain nearly constant 0.9-1.0 Jupiter radii at ages older than 500 Myr. Rotation period and v sin i measurements thus reveal the viewing geometry. Assuming spin-orbit alignment between the host brown dwarf and any surrounding planetary system, brown dwarfs viewed equator-on are excellent targets for the detection of rocky transiting planets. A low host-star luminosity and a tight habitable zone offer the highest probability of detecting transits of Earth-like planets. The optimal contrast between planetary atmospheric lines and the host star’s continuum then offer the best prospects for the detection of biosignatures with JWST. The proposed observations will thus allow us to identify the best targets for exoplanet detection and characterization based on the expected viewing geometry.