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arXiv · 2310.09524

CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES

Grady Robbins·Aaron M. Meisner·Adam C. Schneider·Adam J. Burgasser·J. Davy Kirkpatrick·Jonathan Gagne·Chih-Chun Hsu·Leslie Moranta·Sarah Casewell·Federico Marocco·Roman Gerasimov·Jacqueline K. Faherty·Marc J. Kuchner·Dan Caselden·Michael C. Cushing·Sherelyn Alejandro·The Backyard Worlds·:·Planet 9 Collaboration·Cool Neighbors Collaboration
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Abstract

Y dwarfs, the coolest known spectral class of brown dwarfs, overlap in mass and temperature with giant exoplanets, providing unique laboratories for studying low-temperature atmospheres. However, only a fraction of Y dwarf candidates have been spectroscopically confirmed. We present Keck/NIRES near-infrared spectroscopy of the nearby ($d \approx 6-8$ pc) brown dwarf CWISE J105512.11+544328.3. Although its near-infrared spectrum aligns best with the Y0 standard in the $J$-band, no standard matches well across the full $YJHK$ wavelength range. The CWISE J105512.11+544328.3 NH$_3$-$H$ = 0.427 $\pm$ 0.0012 and CH$_4$-$J$ = 0.0385 $\pm$ 0.0007 absorption indices and absolute Spitzer [4.5] magnitude of 15.18 $\pm$ 0.22 are also indicative of an early Y dwarf rather than a late T dwarf. CWISE J105512.11+544328.3 additionally exhibits the bluest Spitzer [3.6]$-$[4.5] color among all spectroscopically confirmed Y dwarfs. Despite this anomalously blue Spitzer color given its low luminosity, CWISE J105512.11+544328.3 does not show other clear kinematic or spectral indications of low metallicity. Atmospheric model comparisons yield a log(g) $\le$ 4.5 and $T_{\rm eff} \approx 500 \pm 150$ K for this source. We classify CWISE J105512.11+544328.3 as a Y0 (pec) dwarf, adding to the remarkable diversity of the Y-type population. JWST spectroscopy would be crucial to understanding the origin of this Y dwarf's unusual preference for low-gravity models and blue 3-5 $\mu$m color.

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Grady Robbins, Aaron M. Meisner, Adam C. Schneider, Adam J. Burgasser, J. Davy Kirkpatrick, Jonathan Gagne, Chih-Chun Hsu, Leslie Moranta, Sarah Casewell, Federico Marocco, Roman Gerasimov, Jacqueline K. Faherty, Marc J. Kuchner, Dan Caselden, Michael C. Cushing, Sherelyn Alejandro, The Backyard Worlds, :, Planet 9 Collaboration, Cool Neighbors Collaboration. 2023-10-14. CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES. https://arxiv.org/abs/2310.09524

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