# # Program information file # PROGRAM_ID 2024B056 PROGRAM_TITLE Characterization of Benchmark Ultracool M Dwarfs with FGK Wide Binaries PROGRAM_INV1 Chih-Chun Hsu PROGRAM_INV2 PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Ultracool dwarfs [UCDs] are the lowest-mass stars and brown dwarfs with surface temperatures of less than 3,000 K. UCDs cover the effective temperatures of known directly imaged exoplanets, and some are also well-known exoplanet hosts, especially TRAPPIST-1. More UCD exoplanet hosts are expected to be uncovered once the next-generation near-infrared transit instruments are available. However, there exists no empirical and robust abundance calibration for UCDs, making inferring the formation history using abundances of exoplanets challenging. Inconsistent abundances were commonly reported using the popular spectral inversion [retrieval] method among low-mass stars or brown dwarf companions around sun-like stars. To resolve this issue, we are constructing an empirical abundance calibration for M6 to L5 dwarfs that are companions in FGK wide binaries using optical and near-infrared high-resolution spectra. To enable precise calibration as a function of spectral subtype, we propose to classify a subset of 11 UCDs in this sample using IRTF/SpeX spectrograph. PROGRAM_ABSTRACT_END