CWISE J014611.20-050850.0AB: The Widest Known Brown Dwarf Binary in the Field
Shkolnik, Evgenya; Meisner, Aaron M.; Cushing, Michael C.; Kirkpatrick, J. Davy; Burgasser, Adam J.; Casewell, Sarah L.; Schneider, Adam C.; Faherty, Jacqueline K.; Caselden, Dan; Kuchner, Marc J.; Gagné, Jonathan; Aganze, Christian; Backyard Worlds: Planet 9 Collaboration; Andersen, Nikolaj Stevnbak; Patience, Jennifer; Hsu, Chih-Chun; Thévenot, Melina; Kiwy, Frank; Softich, Emma; Gagliuffi, Daniella Bardalez
United States, Canada, United Kingdom
Abstract
While stars are often found in binary systems, brown dwarf binaries are much rarer. Brown dwarf-brown dwarf pairs are typically difficult to resolve because they often have very small separations. Using brown dwarfs discovered with data from the Wide-field Infrared Survey Explorer (WISE) via the Backyard Worlds: Planet 9 citizen science project, we inspected other, higher-resolution, sky surveys for overlooked cold companions. During this process, we discovered the brown dwarf binary system CWISE J0146-0508AB, which we find has a very small chance alignment probability based on the similar proper motions of the components of the system. Using follow-up near-infrared spectroscopy with Keck/NIRES, we determined component spectral types of L4 and L8 (blue), making CWISE J0146-0508AB one of only a few benchmark systems with a blue L dwarf. At an estimated distance of ~40 pc, CWISE J0146-0508AB has a projected separation of ~129 au, making it the widest-separation brown dwarf pair found to date. We find that such a wide separation for a brown dwarf binary may imply formation in a low-density star-forming region.