The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (aka "The Accident")

Abstract

Continued follow-up of WISEA J153429.75-104303.3, announced in Meisner et al (2020), has proven it to have an unusual set of properties. New imaging data from Keck/MOSFIRE and HST/WFC3 show that this object is one of the few faint proper motion sources known with J-ch2 > 8 mag, indicating a very cold temperature consistent with the latest known Y dwarfs. Despite this, it has W1-W2 and ch1-ch2 colors ~1.6 mag bluer than a typical Y dwarf. A new trigonometric parallax measurement from a combination of WISE, Spitzer, and HST astrometry confirms a nearby distance of $16.3_{-1.2}^{+1.4}$ pc and a large transverse velocity of $207.4\pm 15.9$ km/s. The absolute J, W2, and ch2 magnitudes are in line with the coldest known Y dwarfs, despite the highly discrepant W1-W2 and ch1-ch2 colors. We explore possible reasons for the unique traits of this object and conclude that it is most likely an old, metal-poor brown dwarf and possibly the first Y subdwarf. Given that the object has an HST F110W magnitude of 24.7 mag, broad-band spectroscopy and photometry from JWST are the best options for testing this hypothesis.

8 pages, 4 figures, accepted for publication in The Astrophysical Journal Letters

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Cited by in corpus (9)

• unTimely: a Full-sky, Time-Domain unWISE Catalog
• Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs
• Physical properties and trigonometric distance of the peculiar dwarf WISE J181005.5$-$101002.3
• Complete X-ray census of Mdwarfs in the solar Neighborhood I. GJ 745 AB: Coronal-hole Stars in the 10 pc Sample
• Discovery of CWISE J052306.42-015355.4, an Extreme T Subdwarf Candidate
• Silicate Precursor Silane detected in Cold Low-Metallicity Brown Dwarf
• Ammonia-methane ratios from H-band near-infrared spectra of late-T and Y dwarfs
• Ultracool dwarfs candidates based on six years of the Dark Energy Survey data
• Optical constraints on the coldest metal-poor population