Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf
Meisner, Aaron M.; Cushing, Michael C.; Kirkpatrick, J. Davy; Burgasser, Adam J.; Schneider, Adam C.; Marocco, Federico; Faherty, Jacqueline K.; Caselden, Dan; Kuchner, Marc J.; Gagné, Jonathan; Theissen, Christopher; Aganze, Christian; Sainio, Arttu; Backyard Worlds: Planet 9 Collaboration; Vrba, Frederick J.; Munn, Jeffrey A.; Dahm, Scott E.; Bruursema, Justice; Williams, Stephen J.; Rothermich, Austin; Kabatnik, Martin; Vos, Johanna M.; Bickle, Thomas P.; Suárez, Genaro; Hsu, Chih-Chun; Casewell, Sarah; Bardalez Gagliuffi, Daniella
United States, United Kingdom, Canada
Abstract
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 (J - K)MKO color of 2.97 ± 0.03 mag and a J 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 CH4 absorption 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 L8γ-T0γ. We tentatively find that CWISE J0506+0738 is variable at 3-5 μm 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 β Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.