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WISE J072003.20-084651.2B is a Massive T Dwarf

Abstract : We present individual dynamical masses for the nearby M9.5+T5.5 binary WISE J072003.20-084651.2AB, a.k.a. Scholz’s star. Combining high-precision Canada-France-Hawaii Telescope/WIRCam photocenter astrometry and Keck adaptive optics resolved imaging, we measure the first high-quality parallactic distance ({6.80}-0.06+0.05 pc) and orbit ({8.06}-0.25+0.24yr period) for this system composed of a low-mass star and brown dwarf. We find a moderately eccentric orbit (e={0.240}-0.010+0.009), incompatible with previous work based on less data, and dynamical masses of 99 ± 6 {M}Jup} and 66 ± 4 {M}Jup} for the two components. The primary mass is marginally inconsistent (2.1σ) with the empirical mass-magnitude-metallicity relation and models of main-sequence stars. The relatively high mass of the cold ({T}eff}=1250+/- 40 K) brown dwarf companion indicates an age older than a few gigayears, in accord with age estimates for the primary star, and is consistent with our recent estimate of ≈70 {M}Jup} for the stellar/substellar boundary among the field population. Our improved parallax and proper motion, as well as an orbit-corrected system velocity, improve the accuracy of the system’s close encounter with the solar system by an order of magnitude. WISE J0720-0846AB passed within 68.7 ± 2.0 kau of the Sun 80.5 ± 0.7 kyr ago, passing through the outer Oort cloud where comets can have stable orbits.
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https://hal-insu.archives-ouvertes.fr/insu-03702950
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Submitted on : Thursday, June 23, 2022 - 2:58:20 PM
Last modification on : Saturday, June 25, 2022 - 3:06:19 AM

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Trent J. Dupuy, Michael C. Liu, William M. J. Best, Andrew W. Mann, Michael A. Tucker, et al.. WISE J072003.20-084651.2B is a Massive T Dwarf. The Astronomical Journal, 2019, 158, ⟨10.3847/1538-3881/ab3cd1⟩. ⟨insu-03702950⟩

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