Journal ArticleRedder than Red: Discovery of an Exceptionally Red L/T Transition DwarfSchneider, Adam C.; Burgasser, Adam J.; Bruursema, Justice; Munn, Jeffrey A.; Vrba, Frederick J.; Caselden, Dan; Kabatnik, Martin; Rothermich, Austin; Sainio, Arttu; Bickle, Thomas P.; Dahm, Scott E.; Meisner, Aaron M.; Kirkpatrick, J. Davy; Suárez, Genaro; Gagné, Jonathan; Faherty, Jacqueline K.; Vos, Johanna M.; Kuchner, Marc J.; Williams, Stephen J.; Gagliuffi, Daniella Bardalez; Aganze, Christian; Hsu, Chih-Chun; Theissen, Christopher; Cushing, Michael C.; Marocco, Federico; Casewell, Sarah<title>Abstract</title> <p>We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (<italic>J</italic>−<italic>K</italic>)_MKOcolor of 2.97 ± 0.03 mag and a<italic>J</italic>_MKO− W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH₄absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8<italic>γ</italic>–T0<italic>γ</italic>. We tentatively find that CWISE J0506+0738 is variable at 3–5<italic>μ</italic>m based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in the<italic>β</italic>Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.</p>The Astrophysical Journal Letters2023-01-3110468215The Astrophysical Journal Letters9432L162041-8205https://doi.org/10.3847/2041-8213/acb0cd2009177; 2009136National Science Foundation