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New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project

Meisner, Aaron M. and Schneider, Adam C. and Burgasser, Adam J. and Marocco, Federico and Line, Michael R. and Faherty, Jacqueline K. and Kirkpatrick, J. Davy and Caselden, Dan and Kuchner, Marc J. and Gelino, Christopher R. and Gagné, Jonathan and Theissen, Christopher and Gerasimov, Roman and Aganze, Christian and Hsu, Chih-chun and Wisniewski, John P. and Casewell, Sarah L. and Bardalez Gagliuffi, Daniella C. and Logsdon, Sarah E. and Eisenhardt, Peter R. M. and Allers, Katelyn and Debes, John H. and Allen, Michaela B. and Stevnbak Andersen, Nikolaj and Goodman, Sam and Gramaize, Léopold and Martin, David W. and Sainio, Arttu and Cushing, Michael C. (2021) New Candidate Extreme T Subdwarfs from the Backyard Worlds: Planet 9 Citizen Science Project. Astrophysical Journal, 915 (2). Art. No. 120. ISSN 0004-637X. doi:10.3847/1538-4357/ac013c.

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Schneider et al. presented the discovery of WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5, which appear to be the first examples of extreme T-type subdwarfs (esdTs; metallicity ≤−1 dex, T_(eff) ≾ 1400 K). Here, we present new discoveries and follow-up of three T-type subdwarf candidates, with an eye toward expanding the sample of such objects with very low metallicity and extraordinarily high kinematics, properties that suggest membership in the Galactic halo. Keck/NIRES near-infrared spectroscopy of WISEA J155349.96+693355.2, a fast-moving object discovered by the Backyard Worlds: Planet 9 citizen science project, confirms that it is a mid-T subdwarf. With H_(W₂) = 22.3 mag, WISEA J155349.96+693355.2 has the largest W2 reduced proper motion among all spectroscopically confirmed L and T subdwarfs, suggesting that it may be kinematically extreme. Nevertheless, our modeling of the WISEA J155349.96+693355.2 near-infrared spectrum indicates that its metallicity is only mildly subsolar. In analyzing the J155349.96+693355.2 spectrum, we present a new grid of low-temperature, low-metallicity model atmosphere spectra. We also present the discoveries of two new esdT candidates, CWISE J073844.52−664334.6 and CWISE J221706.28−145437.6, based on their large motions and colors similar to those of the two known esdT objects. Finding more esdT examples is a critical step toward mapping out the spectral sequence and observational properties of this newly identified population.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Meisner, Aaron M.0000-0002-1125-7384
Schneider, Adam C.0000-0002-6294-5937
Burgasser, Adam J.0000-0002-6523-9536
Marocco, Federico0000-0001-7519-1700
Line, Michael R.0000-0002-2338-476X
Faherty, Jacqueline K.0000-0001-6251-0573
Kirkpatrick, J. Davy0000-0003-4269-260X
Caselden, Dan0000-0001-7896-5791
Kuchner, Marc J.0000-0002-2387-5489
Gagné, Jonathan0000-0002-2592-9612
Theissen, Christopher0000-0002-9807-5435
Gerasimov, Roman0000-0003-0398-639X
Aganze, Christian0000-0003-2094-9128
Hsu, Chih-chun0000-0002-5370-7494
Wisniewski, John P.0000-0001-9209-1808
Casewell, Sarah L.0000-0003-2478-0120
Bardalez Gagliuffi, Daniella C.0000-0001-8170-7072
Logsdon, Sarah E.0000-0002-9632-9382
Allers, Katelyn0000-0003-0580-7244
Debes, John H.0000-0002-1783-8817
Stevnbak Andersen, Nikolaj0000-0003-4714-3829
Goodman, Sam0000-0003-2236-2320
Gramaize, Léopold0000-0002-8960-4964
Sainio, Arttu0000-0003-4864-5484
Cushing, Michael C.0000-0001-7780-3352
Additional Information:© 2021. The American Astronomical Society. Received 2021 April 30; revised 2021 May 11; accepted 2021 May 12; published 2021 July 15. The Backyard Worlds: Planet 9 team would like to thank the many Zooniverse volunteers who have participated in this project, from providing feedback during the beta review stage to classifying flipbooks to contributing to the discussions on TALK. We would also like to thank the Zooniverse web development team for their work creating and maintaining the Zooniverse platform and the Project Builder tools. This research was supported by NASA grant 2017-ADAP17-0067. This material is based upon work supported by the National Science Foundation under grant No. 2007068, 2009136, and 2009177. F.M. acknowledges support from grant 80NSSC20K0452 under the NASA Astrophysics Data Analysis Program. S.L.C. acknowledges the support of a STFC Ernest Rutherford Fellowship. The CatWISE effort is led by the Jet Propulsion Laboratory, California Institute of Technology, with funding from NASA's Astrophysics Data Analysis Program. Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51447.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. The work of P.R.M.E. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. The UHS is a partnership between the UK STFC, The University of Hawaii, The University of Arizona, Lockheed Martin and NASA. The VISTA Data Flow System pipeline processing and science archive are described in Irwin et al. (2004), Hambly et al. (2008), and Cross et al. (2012). We have used data from VHS DR6. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Based on observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigacion y Desarrollo (Chile), Ministerio de Ciencia, Tecnologia e Innovacion (Argentina), Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (DOI: 10.26093/cds/vizier). The original description of the VizieR service was published in Ochsenbein et al. (2000). This research has made use of the SVO Filter Profile Service ( supported from the Spanish MINECO through grant AYA2017-84089. Facilities: Keck(NIRES - , MOSFIRE) - , WISE - , Spitzer(IRAC) - , Gemini North(NIRI). - Software: WiseView (Caselden et al. 2018), IRAF (Tody 1986), SPLAT (Burgasser & Splat Development Team 2017).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
NASA Hubble FellowshipHST-HF2-51447.001-A
W. M. Keck FoundationUNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2017-84089
Subject Keywords:Brown dwarfs; T dwarfs; T subdwarfs
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Brown dwarfs (185); T dwarfs (1679); T subdwarfs (1680)
Record Number:CaltechAUTHORS:20210727-161800166
Persistent URL:
Official Citation:Aaron M. Meisner et al 2021 ApJ 915 120
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110022
Deposited By: Tony Diaz
Deposited On:28 Jul 2021 19:29
Last Modified:28 Jul 2021 19:29

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