Presentation #309.01 in the session Exoplanet-Star Interactions.
The molecular ion H3+ is a potentially powerful tracer of the ionospheres and thermal structures of Jovian planets, but has never been detected in a planetary mass object outside of the solar system. Models predict that H3+ emission driven by EUV flux and solar wind on hot Jupiters, or by powerful aurorae on brown dwarfs, will be between 102 and 105 times more intense than that of Jupiter. If optimal conditions for the production of emission do exist, the emission may be detectable by current ground-based instruments. We present the first search for H3+ line emission in brown dwarfs with Keck/NIRSPEC L' high-resolution spectroscopy. Additionally, we survey select stars hosting giant planets at semi-major axes near 0.1-0.2 au, which models suggest may be the best planetary targets. No candidate H3+ emission is found. The limits we place on the emission of H3+ from brown dwarfs indicates that auroral generation of H3+ in these environments does not linearly scale from the processes found on Jupiter, plausibly due to deeper atmospheric penetration by precipitating auroral electrons. Detection of H3+ emission in brown dwarfs may be possible with the James Webb Space Telescope (JWST), or future thirty-meter class telescopes.