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Abstract We present three new brown dwarf spectral-binary candidates: CWISE J072708.09−360729.2, CWISE J103604.84−514424.4, and CWISE J134446.62−732053.9, discovered by citizen scientists through the Backyard Worlds: Planet 9 project. Follow-up near-infrared spectroscopy shows that each of these objects is poorly fit by a single near-infrared standard. We constructed binary templates and found significantly better fits, with component types of L7+T4 for CWISE J072708.09−360729.2, L7+T4 for CWISE J103604.84−514424.4, and L7+T7 for CWISE J134446.62−732053.9. However, further investigation of available spectroscopic indices for evidence of binarity and large amplitude variability suggests that CWISE J072708.09−360729.2 may instead be a strong variability candidate. Our analysis offers tentative evidence and characterization of these peculiar brown dwarf sources, emphasizing their value as promising targets for future high-resolution imaging or photometric variability studies. 

Abstract We present the discovery of 118 new ultracool dwarf candidates, discovered using a new machine-learning tool, namedSMDET, applied to time-series images from the Wide-field Infrared Survey Explorer. We gathered photometric and astrometric data to estimate each candidate’s spectral type, distance, and tangential velocity. This sample has a photometrically estimated spectral class distribution of 28 M dwarfs, 64 L dwarfs, and 18 T dwarfs. We also identify a T-subdwarf candidate, two extreme T-subdwarf candidates, and two candidate young ultracool dwarfs. Five objects did not have enough photometric data for any estimations to be made. To validate our estimated spectral types, spectra were collected for two objects, yielding confirmed spectral types of T5 (estimated T5) and T3 (estimated T4). Demonstrating the effectiveness of machine-learning tools as a new large-scale discovery technique. 

Abstract We report the identification of 89 new systems containing ultracool dwarf companions to main-sequence stars and white dwarfs, using the citizen science project Backyard Worlds: Planet 9 and cross-reference between Gaia and CatWISE2020. 32 of these companions and 33 host stars were followed up with spectroscopic observations, with companion spectral types ranging from M7–T9 and host spectral types ranging from G2–M9. These systems exhibit diverse characteristics, from young to old ages, blue to very red spectral morphologies, potential membership to known young moving groups, and evidence of spectral binarity in nine companions. 20 of the host stars in our sample show evidence for higher-order multiplicity, with an additional 11 host stars being resolved binaries themselves. We compare this sample’s characteristics with those of the known stellar binary and exoplanet populations, and find our sample begins to fill in the gap between directly imaged exoplanets and stellar binaries on mass ratio–binding energy plots. With this study, we increase the population of ultracool dwarf companions to FGK stars by ∼42%, and more than triple the known population of ultracool dwarf companions with separations larger than 1000 au, providing excellent targets for future atmospheric retrievals.