A High Resolution H- and K-Band Spectroscopic Sequence of Ultracool Dwarfs

Brown dwarfs are substellar objects too low mass to initiate the hydrogen fusion necessary to be considered stars. Ultracool dwarfs, objects with spectral types of M7 or later, are a mix of low mass stars and brown dwarfs. We have obtained the first high-resolution (R ∼ 45, 000) H- and K-band spectral sequence of ultracool dwarfs with spectral types ranging from M1.5 V to T6, including known low-gravity objects at six spectral types (M9, L0, L1, L2, L3, L5). All spectra were obtained using the Immersion Grating INfrared Spectrometer (IGRINS) at a resolving power of R ∼ 45,000. We compared 22 of our objects to synthetic spectra created from the atmospheric models of Saumon & Marley (2008), to measure specific properties including effective temperature, cloud properties, rotational velocities, and surface gravity.