A SPHEREx Pipeline and Spectral Library for Ultracool Dwarfs

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Abstract We present a Python spectrophotometry extraction tool tailored for fast-moving point sources detected in the SPHEREx mission and use it to construct a set of 0.75–5.0 μ m low-resolution ( λ /Δ λ ≈ 50) spectrophotometry data products based on the SPHEREx Quick Release 2 (QR2) for a set of 6003 L0–Y1 ultracool dwarfs: 2050 known ultracool dwarfs, 3008 known photometric ultracool dwarf candidates, and 945 newly identified ultracool dwarfs. This work more than doubles the number of ultracool dwarfs with spectroscopy, from 3449 to 7402. We provide SPHEREx templates for each spectral subtype and a set of tools to assign automated spectral types. The QR2 data release generates spectrophotometry with an average signal-to-noise per spectral channel above ≈10 for most objects with WISE W2 magnitudes of 14.0 mag and brighter. The compiled data set is made available publicly at https://mocadb.ca , where new spectral compilations from future data releases will also be made available as they are published. These new data provide a significant increase in the number of substellar objects for which the 2.4–5.0 μ m window is now accessible, making it possible to probe important molecular chemistry of key CNOS-bearing species for the coolest brown dwarfs. We flag 2668 ultracool dwarfs as candidate young brown dwarfs, 250 as candidate subdwarfs, and 865 as possibly otherwise peculiar spectroscopic features of interest for future investigation. The SPIFF library presented here opens the door to efficient confirmation of candidate substellar objects and follow-up studies of population-level atmospheric properties of cold brown dwarfs.

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