New Cold Subdwarf Discoveries from Backyard Worlds and a Metallicity Classification System for T Subdwarfs
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| Format: | Preprint |
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2024
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| author | Burgasser, Adam J. Schneider, Adam C. Meisner, Aaron M. Caselden, Dan Hsu, Chih-Chun Gerasimov, Roman Aganze, Christian Softich, Emma Karpoor, Preethi Theissen, Christopher A. Brooks, Hunter Bickle, Thomas P. Gagné, Jonathan Artigau, Étienne Marsset, Michaël Rothermich, Austin Faherty, Jacqueline K. Kirkpatrick, J. Davy Kuchner, Marc J. Andersen, Nikolaj Stevnbak Beaulieu, Paul Colin, Guillaume Gantier, Jean Marc Gramaize, Leopold Hamlet, Les Hinckley, Ken Kabatnik, Martin Kiwy, Frank Martin, David W. Massat, Diego H. Pendrill, William Sainio, Arttu Schümann, Jörg Thévenot, Melina Walla, Jim Wędracki, Zbigniew Worlds, the Backyard : Collaboration, Planet 9 |
| author_facet | Burgasser, Adam J. Schneider, Adam C. Meisner, Aaron M. Caselden, Dan Hsu, Chih-Chun Gerasimov, Roman Aganze, Christian Softich, Emma Karpoor, Preethi Theissen, Christopher A. Brooks, Hunter Bickle, Thomas P. Gagné, Jonathan Artigau, Étienne Marsset, Michaël Rothermich, Austin Faherty, Jacqueline K. Kirkpatrick, J. Davy Kuchner, Marc J. Andersen, Nikolaj Stevnbak Beaulieu, Paul Colin, Guillaume Gantier, Jean Marc Gramaize, Leopold Hamlet, Les Hinckley, Ken Kabatnik, Martin Kiwy, Frank Martin, David W. Massat, Diego H. Pendrill, William Sainio, Arttu Schümann, Jörg Thévenot, Melina Walla, Jim Wędracki, Zbigniew Worlds, the Backyard : Collaboration, Planet 9 |
| contents | We report the results of a spectroscopic survey of candidate T subdwarfs identified by the Backyard Worlds: Planet 9 program. Near-infrared spectra of 31 sources with red $J-W2$ colors and large $J$-band reduced proper motions show varying signatures of subsolar metallicity, including strong collision-induced H$_2$ absorption, obscured methane and water features, and weak K I absorption. These metallicity signatures are supported by spectral model fits and 3D velocities, indicating thick disk and halo population membership for several sources. We identify three new metal-poor T subdwarfs ([M/H] $\lesssim$ $-$0.5), CWISE J062316.19+071505.6, WISEA J152443.14$-$262001.8, and CWISE J211250.11-052925.2; and 19 new "mild" subdwarfs with modest metal deficiency ([M/H] $\lesssim$ $-$0.25). We also identify three metal-rich brown dwarfs with thick disk kinematics. We provide kinematic evidence that the extreme L subdwarf 2MASS J053253.46+824646.5 and the mild T subdwarf CWISE J113010.07+313944.7 may be part of the Thamnos population, while the T subdwarf CWISE J155349.96+693355.2 may be part of the Helmi stream. We define a metallicity classification system for T dwarfs that adds mild subdwarfs (d/sdT), subdwarfs (sdT), and extreme subdwarfs (esdT) to the existing dwarf sequence. We also define a metallicity spectral index that correlates with metallicities inferred from spectral model fits and iron abundances from stellar primaries of benchmark T dwarf companions. This expansion of the T dwarf classification system supports investigations of ancient, metal-poor brown dwarfs now being uncovered in deep imaging and spectroscopic surveys. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2411_01378 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | New Cold Subdwarf Discoveries from Backyard Worlds and a Metallicity Classification System for T Subdwarfs Burgasser, Adam J. Schneider, Adam C. Meisner, Aaron M. Caselden, Dan Hsu, Chih-Chun Gerasimov, Roman Aganze, Christian Softich, Emma Karpoor, Preethi Theissen, Christopher A. Brooks, Hunter Bickle, Thomas P. Gagné, Jonathan Artigau, Étienne Marsset, Michaël Rothermich, Austin Faherty, Jacqueline K. Kirkpatrick, J. Davy Kuchner, Marc J. Andersen, Nikolaj Stevnbak Beaulieu, Paul Colin, Guillaume Gantier, Jean Marc Gramaize, Leopold Hamlet, Les Hinckley, Ken Kabatnik, Martin Kiwy, Frank Martin, David W. Massat, Diego H. Pendrill, William Sainio, Arttu Schümann, Jörg Thévenot, Melina Walla, Jim Wędracki, Zbigniew Worlds, the Backyard : Collaboration, Planet 9 Solar and Stellar Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies We report the results of a spectroscopic survey of candidate T subdwarfs identified by the Backyard Worlds: Planet 9 program. Near-infrared spectra of 31 sources with red $J-W2$ colors and large $J$-band reduced proper motions show varying signatures of subsolar metallicity, including strong collision-induced H$_2$ absorption, obscured methane and water features, and weak K I absorption. These metallicity signatures are supported by spectral model fits and 3D velocities, indicating thick disk and halo population membership for several sources. We identify three new metal-poor T subdwarfs ([M/H] $\lesssim$ $-$0.5), CWISE J062316.19+071505.6, WISEA J152443.14$-$262001.8, and CWISE J211250.11-052925.2; and 19 new "mild" subdwarfs with modest metal deficiency ([M/H] $\lesssim$ $-$0.25). We also identify three metal-rich brown dwarfs with thick disk kinematics. We provide kinematic evidence that the extreme L subdwarf 2MASS J053253.46+824646.5 and the mild T subdwarf CWISE J113010.07+313944.7 may be part of the Thamnos population, while the T subdwarf CWISE J155349.96+693355.2 may be part of the Helmi stream. We define a metallicity classification system for T dwarfs that adds mild subdwarfs (d/sdT), subdwarfs (sdT), and extreme subdwarfs (esdT) to the existing dwarf sequence. We also define a metallicity spectral index that correlates with metallicities inferred from spectral model fits and iron abundances from stellar primaries of benchmark T dwarf companions. This expansion of the T dwarf classification system supports investigations of ancient, metal-poor brown dwarfs now being uncovered in deep imaging and spectroscopic surveys. |
| title | New Cold Subdwarf Discoveries from Backyard Worlds and a Metallicity Classification System for T Subdwarfs |
| topic | Solar and Stellar Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2411.01378 |