Name/Affiliation: Paul B. Rimmer (University of St Andrews)
Cloud Formation, Quenching and Chemistry in Electrified Brown Dwarf Atmospheres
Paul B. Rimmer, Christiane Helling, Craig R. Stark, Camille Bilger Brown dwarf atmospheres are dynamic, engaged in a complicated interplay between gas-phase chemistry, dust and cloud formation, and bombardment by electromagnetic radiation and energetic charged particles. Variable X-ray and radio emission in some brown dwarfs suggests that the atmosphere may be periodically electrified, making way for various hypothetical atmospheric discharge processes. In this presentation, we discuss how cloud formation in DRIFT-PHOENIX model atmospheres is found to enhance the C/O ratio within the cloud layer, and we predict that chemical quenching can transport the carbon-rich chemistry above the cloud top. Atmospheric electrification, whether by cosmic rays and ultraviolet photons in the upper atmosphere, dust-dust collisions in the cloud layer or Alfvén ionization, results in the formation of various ions, and opens up pathways for ion-neutral non-equilibrium chemistry. We predict that atmospheric electrification by cosmic rays can enhance the abundances of complex hydrocarbons and ammonia. These abundances will in turn affect the radiative transfer, the resulting temperature profile, and therefore cloud formation. Progress toward a self-consistent non-equilibrium chemical model will be presented at the end.