Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project

Adam C. Schneider, Aaron M. Meisner, Jonathan Gagné, Jacqueline K. Faherty, Federico Marocco, Adam J. Burgasser, J. Davy Kirkpatrick, Marc J. Kuchner, Léopold Gramaize, Austin Rothermich, Hunter Brooks, Frederick J. Vrba, Daniella Bardalez Gagliuffi, Dan Caselden, Michael C. Cushing, Christopher R. Gelino, Michael R. Line, Sarah L. Casewell, John H. Debes, Christian AganzeAndrew Ayala, Roman Gerasimov, Eileen C. Gonzales, Chih Chun Hsu, Rocio Kiman, Mark Popinchalk, Christopher Theissen

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


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 M Jup. 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.

Original languageEnglish (US)
Article number140
JournalAstrophysical Journal
Issue number2
StatePublished - Nov 10 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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