Orbit and Dynamical Mass of the Late-T Dwarf GL 758 B

Creators: Bowler, Brendan P.; Dupuy, Trent J.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Fulton, Benjamin J.; Petigura, Erik A.; Howard, Andrew W.; Hirsch, Lea; Kratter, Kaitlin M.; Crepp, Justin R.; Biller, Beth A.; Johnson, Marshall C.; Wittenmyer, Robert A.

Abstract

Gl 758 B is a late-T dwarf orbiting a metal-rich Sun-like star at a projected separation of ρ ≈ 1farcs6 (25 au). We present four epochs of astrometry of this system with NIRC2 at Keck Observatory spanning 2010 to 2017 together with 630 radial velocities (RVs) of the host star acquired over the past two decades from McDonald Observatory, Keck Observatory, and the Automated Planet Finder at Lick Observatory. The RVs reveal that Gl 758 is accelerating with an evolving rate that varies between 2 and 5 m s^(−1) yr^(−1), consistent with the expected influence of the imaged companion Gl 758 B. A joint fit of the RVs and astrometry yields a dynamical mass of 42_(-7)^(+19) M_(Jup) for the companion with a robust lower limit of 30.5 M_(Jup) at the 4-σ level. Gl 758 B is on an eccentric orbit (e = 0.26–0.67 at 95% confidence) with a semimajor axis of a = 21.1_(-1.3)^(+2.7) au and an orbital period of P = 96_(-9)^(+21) yr, which takes it within ≈9 au from its host star at periastron passage. Substellar evolutionary models generally underpredict the mass of Gl 758 B for nominal ages of 1–6 Gyr that have previously been adopted for the host star. This discrepancy can be reconciled if the system is older—which is consistent with activity indicators and recent isochrone fitting of the host star—or alternatively if the models are systematically overluminous by ≈0.1–0.2 dex. Gl 758 B is currently the lowest-mass directly imaged companion inducing a measured acceleration on its host star. In the future, bridging RVs and high-contrast imaging with the next generation of extremely large telescopes and space-based facilities will open the door to the first dynamical mass measurements of imaged exoplanets.

Additional Information

© 2018. The American Astronomical Society. Received 2018 January 1; revised 2018 February 21; accepted 2018 February 23; published 2018 March 21. We are especially grateful to the many dedicated observers and support staff at McDonald Observatory, Keck, and APF who contributed to this expansive data set over the years, in particular S. Barnes, I. Ramirez, E. Brugamyer, C. Caldwell, K. Gullikson, P. Robertson, G. Marcy, H. Isaacson, D. Fischer, K. Peek, E. Sinukoff, J. Johnson, L. Weiss, G. Torres, G. Bakos, T. Morton, J. Brewer, S. Pineda, J. Wang, C. Clanton, M. Bottom, and J. Curtis. This study would not have been possible without this communal assistance and resourcefulness. We thank Chris Sneden for many helpful discussions on the properties of the host star and Ricky Nilsson for sharing the spectrum of Gl 758 B from P1640. The McDonald Observatory Planet Search is supported by the National Science Foundation through grant AST-1313075. This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Support for this work was provided by NASA through Hubble Fellowship grants HST-HF2-51365.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Keck:II (NIRC2) - , Keck:I (HIRES) - , Smith (Tull Coudé Spectrograph) - , APF (Levy). -

Attached Files

Published - Bowler_2018_AJ_155_159.pdf

Accepted Version - 1802.10126

Files

Bowler_2018_AJ_155_159.pdf

Files (6.2 MB)

Name	Size	Download all
1802.10126 md5:d0c7b5882c31715a9990d575e65d7ddd	3.2 MB	Download
Bowler_2018_AJ_155_159.pdf md5:8f6e0c6ca75535d508bb8220dd5f28ca	3.0 MB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes