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

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, wi...

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Published in:The Astrophysical journal 2021-07, Vol.915 (2), p.120
Main Authors: Meisner, Aaron M., Schneider, Adam C., Burgasser, Adam J., Marocco, Federico, Line, Michael R., Faherty, Jacqueline K., Kirkpatrick, J. Davy, Caselden, Dan, Kuchner, Marc J., Gelino, Christopher R., Gagné, Jonathan, Theissen, Christopher, Gerasimov, Roman, Aganze, Christian, Hsu, Chih-chun, Wisniewski, John P., Casewell, Sarah L., Bardalez Gagliuffi, Daniella C., Logsdon, Sarah E., Eisenhardt, Peter R. M., Allers, Katelyn, Debes, John H., Allen, Michaela B., Stevnbak Andersen, Nikolaj, Goodman, Sam, Gramaize, Léopold, Martin, David W., Sainio, Arttu, Cushing, Michael C.
Format: Article
Language:English
Subjects:
Astrophysics
Atmospheric models
Brown dwarfs
Extrasolar planets
Galactic halos
Infrared analysis
Infrared spectra
Infrared spectroscopy
Kinematics
Low temperature
Metallicity
Near infrared radiation
Near infrared spectroscopy
Planets
Spectrum analysis
T dwarfs
T subdwarfs
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Summary: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.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ac013c