Deriving Parameters of Ultracool Dwarfs Using High-Resolution Spectroscopy

Ultracool dwarfs, a mix of the lowest mass stars and brown dwarfs (substellar object too low mass to initiate stable hydrogen fusion), are the lowest mass products of star formation. The lack of a stable internal energy source causes brown dwarfs to cool as they age, causing them to exhibit a mass-luminosity-age relation, which complicates efforts to measure their fundamental parameters (e.g. M, Teff). We have obtained the first high-resolution (R˜45,000) H- and K-band spectral sequence of ultracool dwarfs using the Immersion Grating INfrared Spectrometer (IGRINS). Our sequence spans the spectral types from M1.5V to T6, and includes known low-gravity objects at six spectral types ranging (M9, L0, L1, L2, L3, L5), which we plan to use to empirically search for gravity sensitive features. We have compared 22 of our objects to synthetic spectra created from the model atmospheres of Saumon & Marley (2008) to measure specific properties including effective temperature, cloud properties, rotational velocities, and surface gravity.