The Leech exoplanet imaging survey: Characterization of the coldest directly imaged exoplanet, GJ 504 b, and evidence for superstellar metallicity

Andrew J. Skemer, Caroline V. Morley, Neil T. Zimmerman, Michael F. Skrutskie, Jarron Leisenring, Esther Buenzli, Mickael Bonnefoy, Vanessa Bailey, Philip M Hinz, Denis Defrére, Simone Esposito, Daniel Apai, Beth Biller, Wolfgang Brandner, Laird M Close, Justin R. Crepp, Robert J. De Rosa, Silvano Desidera, Joshua A Eisner, Jonathan FortneyRichard Freedman, Thomas Henning, Karl Heinz Hofmann, Taisiya Kopytova, Roxana Lupu, Anne Lise Maire, Jared R. Males, Mark Marley, Katie Morzinski, Apurva Oza, Jenny Patience, Abhijith Rajan, George H. Rieke, Dieter Schertl, Joshua Schlieder, Jordan Stone, Kate Su, Amali Vaz, Channon Visscher, Kimberly Ward-Duong, Gerd Weigelt, Charles E. Woodward

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

As gas giant planets and brown dwarfs radiate away the residual heat from their formation, they cool through a spectral type transition from L to T, which encompasses the dissipation of cloud opacity and the appearance of strong methane absorption. While there are hundreds of known T-type brown dwarfs, the first generation of directly imaged exoplanets were all L type. Recently, Kuzuhara et al. announced the discovery of GJ 504 b, the first T dwarf exoplanet. GJ 504 b provides a unique opportunity to study the atmosphere of a new type of exoplanet with a ∼500 K temperature that bridges the gap between the first directly imaged planets (∼1000 K) and our own solar system's Jupiter (∼130 K). We observed GJ 504 b in three narrow L-band filters (3.71, 3.88, and 4.00 μm), spanning the red end of the broad methane fundamental absorption feature (3.3 μm) as part of the LBTI Exozodi Exoplanet Common Hunt (LEECH) exoplanet imaging survey. By comparing our new photometry and literature photometry with a grid of custom model atmospheres, we were able to fit GJ 504 b's unusual spectral energy distribution for the first time. We find that GJ 504 b is well fit by models with the following parameters: Teff = 544 ± 10 K, g <600 m s-2, [M/H] = 0.60 ± 0.12, cloud opacity parameter of fsed = 2-5, R = 0.96 ± 0.07 RJup, and log(L) = -6.13 ± 0.03 Lo, implying a hot start mass of 3-30 Mjup for a conservative age range of 0.1-6.5 Gyr. Of particular interest, our model fits suggest that GJ 504 b has a superstellar metallicity. Since planet formation can create objects with nonstellar metallicities, while binary star formation cannot, this result suggests that GJ 504 b formed like a planet, not like a binary companion.

Original languageEnglish (US)
Article number166
JournalAstrophysical Journal
Volume817
Issue number2
DOIs
StatePublished - Feb 1 2016

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Keywords

  • planets and satellites: atmospheres
  • planets and satellites: composition
  • planets and satellites: gaseous planets
  • stars: individual (GJ 504)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Skemer, A. J., Morley, C. V., Zimmerman, N. T., Skrutskie, M. F., Leisenring, J., Buenzli, E., Bonnefoy, M., Bailey, V., Hinz, P. M., Defrére, D., Esposito, S., Apai, D., Biller, B., Brandner, W., Close, L. M., Crepp, J. R., De Rosa, R. J., Desidera, S., Eisner, J. A., ... Woodward, C. E. (2016). The Leech exoplanet imaging survey: Characterization of the coldest directly imaged exoplanet, GJ 504 b, and evidence for superstellar metallicity. Astrophysical Journal, 817(2), [166]. https://doi.org/10.3847/0004-637X/817/2/166