# # Program information file # PROGRAM_ID 2021B118 PROGRAM_TITLE Characterizing New Ultracool Dwarfs with IRTF/SpeX PROGRAM_INV1 Benjamin Rackham PROGRAM_INV2 Julien de Wit PROGRAM_INV3 Maximilian Guenther PROGRAM_INV4 Daniel Sebastian PROGRAM_INV5 Adam Burgasser PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Planetary transits of ultracool dwarfs [UCDs, T_eff < 3000 K] provide our only opportunity to characterize terrestrial exoplanets in detail in the next 20 years. The SPECULOOS Transit Survey is leading the effort to discover these worlds transiting nearby UCDs using a network of six 1-meter telescopes on three continents. Of the 366 highest-priority SPECULOOS targets, those for which JWST observations would best probe the atmospheres of any detected transiting planets, roughly a quarter are candidate ultracool dwarfs that have only recently been identified with Gaia DR2 and lack spectra suitable for stellar characterization. Here we propose to address this need by collecting medium-resolution NIR spectra of 79 equatorial and northern targets with SpeX/IRTF. These spectra will allow us to probe binarity, assign spectral types, and measure molecular band strengths and equivalent widths of atomic lines for each of our targets, providing useful discriminators of temperature, mass, gravity, metallicity, and condensation chemistry. The final output of this program will be a catalog of spectral types and fundamental physical parameters that will fill in a major gap in our understanding of the nearby ultracool dwarf population. Complementary observations for southern targets are being carried out on Magellan/FIRE, and our full sample of published spectra will be made available in an online archive. PROGRAM_ABSTRACT_END