Program: GN-2021A-FT-113

The carbon-to-oxygen ratio in brown dwarfs and giant extra-solar planets provides a link between present atmospheric composition and formation pathway, allowing studies into the complex and uncertain origins of these objects. Measurements of the carbon-to-oxygen ratio in brown dwarfs are severely lacking, in large part due to past deficiencies in atmosphere models. To address this, we have been utilizing the brand-new ATMO 2020 atmosphere model grid to include non-solar carbon-to-oxygen ratios, benefitting from a decade of improvements to the molecular opacities and chemistry. Crucially, these new models reveal that we cannot reliably disentangle the C/O ratio of cool brown dwarfs from other atmospheric processes with the spectral resolution, signal-to-noise and/or incomplete wavelength coverage of spectra currently available in the literature. We therefore propose for high-quality Gemini/GNIRS spectroscopy that, combined with our state- of-the-art atmosphere models, will enable us for the first time to determine the carbon-to-oxygen ratios for two benchmark brown dwarfs, GJ 570D and Ross 458C. These measurements will shed light on compositions and formation mechanisms through the substellar regime, and will be a valuable stepping stone in validating our ability determine the carbon-to-oxygen ratio of gas giant exoplanets.