# # Program information file # PROGRAM_ID 2022A047 PROGRAM_TITLE Characterizing New Nearby Ultracool Dwarfs with IRTF/SpeX PROGRAM_INV1 Benjamin Rackham PROGRAM_INV2 Adam Burgasser PROGRAM_INV3 Elisabeth Newton PROGRAM_INV4 Julien de Wit PROGRAM_INV5 Daniel Sebastian 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. Large efforts to discover these worlds transiting nearby UCDs are ongoing with ground- and space-based platforms. However, of the 366 highest-priority targets, those for which JWST observations would best probe the atmospheres of any detected transiting planets, roughly a quarter are candidate UCDs 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 53 equatorial and northern targets with SpeX/IRTF. The primary goal of this program will be guide ongoing transit searches by identifying high-priority [e.g., metal-rich] and low priority [e.g., false positives, binaries, or metal-poor] targets. 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. Combining spectra from IRTF/SpeX and Lick/KAST in the north and Magellan/FIRE and Magellan/LDSS3 in the south, the final output of this program will be a catalog of spectral types and fundamental physical parameters that will guide planet searches, fill in a major gap in our understanding of nearby UCDs, and support future studies of this population. PROGRAM_ABSTRACT_END