The Astrophysical Journal, 915:120 (14pp), 2021 July 10 https://doi.org/10.3847/1538-4357/ac013c © 2021. The American Astronomical Society. All rights reserved. New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project Aaron M. Meisner1 , Adam C. Schneider2,3 , Adam J. Burgasser4 , Federico Marocco5 , Michael R. Line6 , Jacqueline K. Faherty7 , J. Davy Kirkpatrick5 , Dan Caselden8 , Marc J. Kuchner9 , Christopher R. Gelino5, Jonathan Gagné10,11 , Christopher Theissen4,19 , Roman Gerasimov4 , Christian Aganze4 , Chih-chun Hsu4 , John P. Wisniewski12 , Sarah L. Casewell13 , Daniella C. Bardalez Gagliuffi7 , Sarah E. Logsdon1 , Peter R. M. Eisenhardt14, Katelyn Allers15 , John H. Debes16 , Michaela B. Allen9, Nikolaj Stevnbak Andersen17 , Sam Goodman17 , Léopold Gramaize17 , David W. Martin17, Arttu Sainio17 , and Michael C. Cushing18 The Backyard Worlds: Planet 9 Collaboration 1 NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA;
[email protected] 2 United States Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Rd., Flagstaff, AZ 86005, USA 3 Department of Physics and Astronomy, George Mason University, MS3F3, 4400 University Drive, Fairfax, VA 22030, USA 4 Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093, USA 5 IPAC, Mail Code 100-22, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA 6 School of Earth & Space Exploration, Arizona State University,