Program: GN-2023B-Q-324

The carbon-to-oxygen ratio in brown dwarfs and gas-giant exoplanets 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 expanding our recently published ATMO 2020 atmosphere model grid to include non-solar carbon-to-oxygen ratios, benefitting from a range 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 a sample of cool brown dwarfs and free-floating planets. These measurements will shed light on compositions and formation mechanisms through the substellar regime down to 2 Jupiter masses, and will be a valuable stepping stone in validating our ability determine the carbon-to-oxygen ratio of gas-giant exoplanets.