Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project
Debes, John H.; Gonzales, Eileen C.; Kiman, Rocio; Meisner, Aaron M.; Line, Michael R.; Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R.; Burgasser, Adam J.; Casewell, Sarah L.; Schneider, Adam C.; Marocco, Federico; Faherty, Jacqueline K.; Caselden, Dan; Kuchner, Marc J.; Gagné, Jonathan; Theissen, Christopher; Gerasimov, Roman; Aganze, Christian; Gramaize, Léopold; Backyard Worlds: Planet 9 Collaboration; Vrba, Frederick J.; Rothermich, Austin; Brooks, Hunter; Popinchalk, Mark; Hsu, Chih-Chun; Ayala, Andrew; Bardalez Gagliuffi, Daniella
United States, Canada, United Kingdom
Abstract
Through the Backyard Worlds: Planet 9 citizen science project, we have identified a wide-separation (~10', ~9900 au projected) substellar companion to the nearby (~17.5 pc), mid-M dwarf Ross 19. We have developed a new formalism for determining chance alignment probabilities based on the BANYAN Σ tool, and find a 100% probability that this is a physically associated pair. Through a detailed examination of Ross 19A, we find that the system is metal-poor ([Fe/H] = -0.40 ± 0.12) with an age of ${7.2}_{-3.6}^{+3.8}$ Gyr. Combining new and existing photometry and astrometry, we find that Ross 19B is one of the coldest known wide-separation companions, with a spectral type on the T/Y boundary, an effective temperature of ${500}_{-100}^{+115}$ K, and a mass in the range 15-40 MJup. This new, extremely cold benchmark companion is a compelling target for detailed characterization with future spectroscopic observations using facilities such as the Hubble Space Telescope or James Webb Space Telescope.