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

Creators: Dupuy, Trent J.; Liu, Michael C.; Best, William M. J.; Mann, Andrew W.; Tucker, Michael A.; Zhang, Zhoujian; Baraffe, Isabelle; Chabrier, Gilles; Forveille, Thierry; Metchev, Stanimir A.; Tremblin, Pascal; Do, Aaron; Payne, Anna V.; Shappee, B. J.; Bond, Charlotte Z.; Cetre, Sylvain; Chun, Mark; Delorme, Jacques-Robert; Jovanovic, Nemanja; Lilley, Scott; Mawet, Dimitri; Ragland, Sam; Wetherell, Ed; Wizinowich, Peter

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^(+0.05)_(−0.06) pc) and orbit (8.06^(+0.24)_(−0.25) yr period) for this system composed of a low-mass star and brown dwarf. We find a moderately eccentric orbit (e = 0.240^(+0.009)_(−0.010)), 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.

Additional Information

© 2019 The American Astronomical Society. Received 2019 June 7; revised 2019 August 11; accepted 2019 August 18; published 2019 October. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on data obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, at the Canada–France–Hawaii Telescope, which is operated by the National Research Council of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. T.J.D. acknowledges research support from Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Brazil, Canada, Chile, the Republic of Korea, and the United States of America. M.C.L. acknowledges National Science Foundation (NSF) grant AST-1518339. The near-infrared pyramid wavefront sensor is supported by NSF grant AST-1611623. The camera used with the pyramid wavefront sensor is provided by Don Hall with support from the National Science Foundation under grant AST-1106391. M.A.T. acknowledges support from the DOE CSGF through grant DE-SC0019323. Our research has employed NASA ADS; SIMBAD; VizieR; and J. R. A. Davenport's IDL implementation of the cubehelix color scheme (Green 2011). Facilities: Keck:II (LGS AO - , NIRC2 - , PyWFS AO) - , CFHT (WIRCam) - , IRTF (SpeX) - , UH:2.2 m (SNIFS). - Software: Spextool (Cushing et al. 2004), emcee (Foreman-Mackey et al. 2013), M_-M_K- (Mann et al. 2019).

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