Brown Dwarf Retrievals on FIRE! Medium Resolution Retrieval of a T9 Dwarf

Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Recently, atmospheric retrieval approaches have been successfully applied to a number of low-resolution (R≈100) spectra of T and Y dwarfs, yielding constraints on the abundances of chemical species and temperature structures of these atmospheres. Medium-resolution spectra of brown dwarfs may offer additional insight, as molecular features should be more easily disentangled from one another and the thermal structure of the upper atmosphere is more readily probed. Furthermore, kinematic information such as the radial and rotation velocities of these objects can be retrieved directly from the spectra. We present preliminary results from applying the CHIMERA retrieval framework to a high signal-to-noise, medium-resolution (R≈6000) FIRE spectrum of a T9 dwarf from 0.85-2.5 microns. At 60x higher spectral resolution than previous retrievals, a number of novel challenges arise, which we explore. We compare these retrieval results to those obtained for a R≈100 spectrum of the same object, revealing how constraints on atmospheric abundances greatly improve with increased spectral resolution. We discuss lessons learned from this work in preparation for JWST observations of substellar objects at medium (R≈2700) spectral resolution.