WISEA J041451.67–585456.7 and WISEA J181006.18–101000.5: The First Extreme T-type Subdwarfs?

Creators: Schneider, Adam C.; Burgasser, Adam J.; Gerasimov, Roman; Marocco, Federico; Gagné, Jonathan; Goodman, Sam; Beaulieu, Paul; Pendrill, William; Rothermich, Austin; Sainio, Arttu; Kuchner, Marc J.; Caselden, Dan; Meisner, Aaron M.; Faherty, Jacqueline K.; Mamajek, Eric E.; Hsu, Chih-Chun; Greco, Jennifer J.; Cushing, Michael C.; Kirkpatrick, J. Davy; Bardalez-Gagliuffi, Daniella C.; Logsdon, Sarah E.; Allers, Katelyn; Debes, John H.; Backyard Worlds: Planet 9 Collaboration

Abstract

We present the discoveries of WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5, two low-temperature (1200–1400 K), high proper motion T-type subdwarfs. Both objects were discovered via their high proper motion (>0".5 yr⁻¹); WISEA J181006.18−101000.5 as part of the NEOWISE proper motion survey and WISEA J041451.67−585456.7 as part of the citizen science project Backyard Worlds; Planet 9. We have confirmed both as brown dwarfs with follow-up near-infrared spectroscopy. Their spectra and near-infrared colors are unique among known brown dwarfs, with some colors consistent with L-type brown dwarfs and other colors resembling those of the latest-type T dwarfs. While no forward model consistently reproduces the features seen in their near-infrared spectra, the closest matches suggest very low metallicities ([Fe/H] ⩽ −1), making these objects likely the first examples of extreme subdwarfs of the T spectral class (esdT). WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5 are found to be part of a small population of objects that occupy the "substellar transition zone," and have the lowest masses and effective temperatures of all objects in this group.

Additional Information

© 2020. The American Astronomical Society. Received 2020 April 16; revised 2020 May 19; accepted 2020 June 4; published 2020 July 24. This research was supported by NASA Astrophysics Data Analysis Program grant NNH17AE75I. 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. This work used the Extreme Science and Engineering Discovery Environment (XSEDE) Comet cluster at the San Diego Supercomputer Center (program AST190045). XSEDE is supported by National Science Foundation grant number ACI-1548562 (Towns et al. 2014). 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, and NEOWISE, which is a project of the Jet Propulsion Laboratory/California Institute of Technology. WISE and NEOWISE are funded by the National Aeronautics and Space Administration. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

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Accepted Version - 2007.03836.pdf

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