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

Abstract

Schneider et al. (2020) 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.

arXiv commentaccepted for publication in ApJ; models available at https://doi.org/10.7910/DVN/SJRXUO

References in corpus (68)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The James Webb Space Telescope
• Overview of the DESI Legacy Imaging Surveys
• The VizieR database of Astronomical Catalogues
• A Method of Correcting Near-Infrared Spectra for Telluric Absorption
• The UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
• The WFCAM Science Archive
• ExoMol: molecular line lists for exoplanet and other atmospheres
• ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K
• The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• A variationally computed line list for hot NH3
• unWISE: unblurred coadds of the WISE imaging
• The 2MASS Wide-Field T Dwarf Search. III. Seven New T Dwarfs and Other Cool Dwarf Discoveries
• The CatWISE2020 Catalog
• H- Opacity and Water Dissociation in the Dayside Atmosphere of the Very Hot Gas Giant WASP-18 b
• ExoMol Molecular linelists -- XXXIII. The spectrum of Titanium Oxide
• ExoMol line lists XVIII. The high temperature spectrum of VO
• The VISTA Science Archive
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets
• Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun
• ExoMol line lists VII: The rotation-vibration spectrum of phosphine up to 1500 K
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• The UKIRT Hemisphere Survey: Definition and J-band Data Release
• The DECam Plane Survey: Optical photometry of two billion objects in the southern Galactic plane
• ExoMol line lists II: The ro-vibrational spectrum of SiO
• New study of the line profiles of sodium perturbed by H2
• ExoMol molecular line lists V: The ro-vibrational spectra of NaCl and KCl
• New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown dwarfs
• A Study of the Diverse T Dwarf Population Revealed by WISE
• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• Treatment of overlapping gaseous absorption with the correlated-k method in hot Jupiter and brown dwarf atmosphere models
• The CatWISE Preliminary Catalog: Motions from $WISE$ and $NEOWISE$ Data
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs II: Properties of 11 T-dwarfs
• A theoretical look at the direct detection of giant planets outside the Solar System
• A HST/WFC3 Thermal Emission Spectrum of the Hot Jupiter HAT-P-7b
• CRIRES spectroscopy and empirical line-by-line identification of FeH molecular absorption in an M dwarf
• Time-resolved WISE/NEOWISE Coadds
• The First Brown Dwarf Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
• The Exemplar T8 Subdwarf Companion of Wolf 1130
• A Uniform Retrieval Analysis of Ultracool Dwarfs. III. Properties of Y-Dwarfs
• ExoMol line lists XXVIII: The rovibronic spectrum of AlH
• A transition between the hot and the ultra-hot Jupiter atmospheres
• A Proper Motion Survey Using the First Sky Pass of NEOWISE-Reactivation Data
• Ground- and Space-based Detection of the Thermal Emission Spectrum of the Transiting Hot Jupiter KELT-2Ab
• Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
• A H13CN/HN13C linelist, model atmospheres and synthetic spectra for carbon stars
• Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
• WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?
• Primeval very low-mass stars and brown dwarfs - IV. New L subdwarfs, Gaia astrometry, population properties, and a blue brown dwarf binary
• Retrieval of SDSS J1416+1348AB
• The Influence of H2O Pressure Broadening in High Metallicity Exoplanet Atmospheres
• A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project
• Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Luminous Infrared Galaxy Candidates
• A deep WISE search for very late type objects and the discovery of two halo/thick-disk T dwarfs: WISE 0013+0634 and WISE 0833+0052
• WISEA J083011.95+283716.0: A Missing Link Planetary-Mass Object
• An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Sub-Solar Water Abundance
• First Data Release of the All-sky NOAO Source Catalog
• WISE2150-7520AB: A very low mass, wide co-moving brown dwarf system discovered through the citizen science project Backyard Worlds: Planet 9
• The discovery of a T6.5 subdwarf
• CWISEP J193518.59$-$154620.3: An Extremely Cold Brown Dwarf in the Solar Neighborhood Discovered with CatWISE
• Spectroscopic Follow-Up of Discoveries from the NEOWISE Proper Motion Survey
• The TESS Phase Curve of KELT-1b Suggests a High Dayside Albedo
• Understanding Fundamental Properties and Atmospheric Features of Subdwarfs via a Case Study of SDSS J125637.13-022452.4

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• Overview of the DESI Milky Way Survey
• unTimely: a Full-sky, Time-Domain unWISE Catalog
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• Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf
• Discovery of CWISE J052306.42-015355.4, an Extreme T Subdwarf Candidate
• Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project
• A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late-T Dwarfs
• WISEA J052305.94-015356.1: A New EsdT Candidate