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The TRENDS High-contrast Imaging Survey. VI. Discovery of a Mass, Age, and Metallicity Benchmark Brown Dwarf

Crepp, Justin R. and Gonzales, Erica J. and Bechter, Eric B. and Montet, Benjamin T. and Johnson, John Asher and Piskorz, Danielle and Howard, Andrew W. and Isaacson, Howard (2016) The TRENDS High-contrast Imaging Survey. VI. Discovery of a Mass, Age, and Metallicity Benchmark Brown Dwarf. Astrophysical Journal, 831 (2). Art. No. 136. ISSN 0004-637X.

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The mass and age of substellar objects are degenerate parameters leaving the evolutionary state of brown dwarfs ambiguous without additional information. Theoretical models are normally used to help distinguish between old, massive brown dwarfs and young, low-mass brown dwarfs but these models have yet to be properly calibrated. We have carried out an infrared high-contrast imaging program with the goal of detecting substellar objects as companions to nearby stars to help break degeneracies in inferred physical properties such as mass, age, and composition. Rather than using imaging observations alone, our targets are pre-selected based on the existence of dynamical accelerations informed from years of stellar radial velocity (RV) measurements. In this paper, we present the discovery of a rare benchmark brown dwarf orbiting the nearby (d = 18.69 ± 0.19 pc), solar-type (G9V) star HD 4747 ([Fe/H] = −0.22 ± 0.04) with a projected separation of only ρ = 11.3 ± 0.2 au (θ = 0”.6). Precise Doppler measurements taken over 18 years reveal the companion's orbit and allow us to place strong constraints on its mass using dynamics (m sin i = 55.3 ± 1.9M_(Jup)). Relative photometry (ΔK_s = 9.05 ± 0.14, M_K_s = 13.00 ± 0.14, K_s – L’ = 1.34 ± 0.46) indicates that HD 4747 B is most likely a late-type L-dwarf and, if near the L/T transition, an intriguing source for studying cloud physics, variability, and polarization. We estimate a model-dependent mass of m = 72^(+3)_(-13) M_(Jup) for an age of 3.3^(+2.3)_(-1.9) Gyr based on gyrochronology. Combining astrometric measurements with RV data, we calculate the companion dynamical mass (m = 60.2 ± 3.3M_(Jup)) and orbit (e = 0.740 ± 0.002) directly. As a new mass, age, and metallicity benchmark, HD 4747 B will serve as a laboratory for precision astrophysics to test theoretical models that describe the emergent radiation of brown dwarfs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Crepp, Justin R.0000-0003-0800-0593
Montet, Benjamin T.0000-0001-7516-8308
Johnson, John Asher0000-0001-9808-7172
Piskorz, Danielle0000-0003-4451-2342
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Additional Information:© 2016 American Astronomical Society. Received 2016 March 26; revised 2016 May 20; accepted 2016 June 3; published 2016 November 3. We thank the many California Planet Search observers for help over the years securing precise RV measurements that ultimately led to the direct imaging discovery of HD 4747 B. Chris Matthews estimated the L' apparent magnitude of HD 4747 A by fitting an SED to its flux measured at visible and near-infrared wavelengths. 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. B.T.M. is supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE-1144469. The TRENDS high-contrast imaging program is supported in part by NASA Origins grant NNX13AB03G and PI Crepp's NASA Early Career Fellowship. We are also grateful for the vision and support of the Potenziani family.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1144469
Subject Keywords:astrometry – stars: individual (HD 4747) – techniques: high angular resolution – techniques: radial velocities
Issue or Number:2
Record Number:CaltechAUTHORS:20161102-133237424
Persistent URL:
Official Citation:Justin R. Crepp et al 2016 ApJ 831 136
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71678
Deposited By: Tony Diaz
Deposited On:02 Nov 2016 23:17
Last Modified:09 Mar 2020 13:18

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