TY - JOUR
T1 - New Candidate Extreme T Subdwarfs from the Backyard Worlds
T2 - Planet 9 Citizen Science Project
AU - The Backyard Worlds: Planet 9 Collaboration
AU - Meisner, Aaron M.
AU - Schneider, Adam C.
AU - Burgasser, Adam J.
AU - Marocco, Federico
AU - Line, Michael R.
AU - Faherty, Jacqueline K.
AU - Kirkpatrick, J. Davy
AU - Caselden, Dan
AU - Kuchner, Marc J.
AU - Gelino, Christopher R.
AU - Gagné, Jonathan
AU - Theissen, Christopher
AU - Gerasimov, Roman
AU - Aganze, Christian
AU - Hsu, Chih Chun
AU - Wisniewski, John P.
AU - Casewell, Sarah L.
AU - Bardalez Gagliuffi, Daniella C.
AU - Logsdon, Sarah E.
AU - Eisenhardt, Peter R.M.
AU - Allers, Katelyn
AU - Debes, John H.
AU - Allen, Michaela B.
AU - Stevnbak Andersen, Nikolaj
AU - Goodman, Sam
AU - Gramaize, Léopold
AU - Martin, David W.
AU - Sainio, Arttu
AU - Cushing, Michael C.
N1 - Publisher Copyright:
© 2021. The American Astronomical Society. All rights reserved..
PY - 2021/7/10
Y1 - 2021/7/10
N2 - 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.
AB - 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.
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UR - http://www.scopus.com/inward/citedby.url?scp=85111292750&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/ac013c
DO - 10.3847/1538-4357/ac013c
M3 - Article
AN - SCOPUS:85111292750
SN - 0004-637X
VL - 915
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 120
ER -