THE LEECH EXOPLANET IMAGING SURVEY: CHARACTERIZATION OF THE COLDEST DIRECTLY IMAGED EXOPLANET, GJ 504 b, AND EVIDENCE FOR SUPERSTELLAR METALLICITY
- Steward Observatory, University of Arizona, 933 North Cherry Ave. Tucson, AZ 85721 (United States)
- University of California, Santa Cruz, 1156 High St. Santa Cruz, CA 95064 (United States)
- Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg (Germany)
- University of Virginia, 530 McCormick Rd., Charlottesville, VA 22904 (United States)
- Istituto Nazionale di Astrofisica-Arcetri Astrophysical Observatory, Largo Enrico Fermi 5, 50125, Florence (Italy)
- Notre Dame University, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)
- Arizona State University, 781 South Terrace Rd, Tempe, AZ 85281 (United States)
- Istituto Nazionale di Astrofisica-Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, 35122 Padova (Italy)
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: T{sub eff} = 544 ± 10 K, g < 600 m s{sup −2}, [M/H] = 0.60 ± 0.12, cloud opacity parameter of f{sub sed} = 2–5, R = 0.96 ± 0.07 R{sub Jup}, and log(L) = −6.13 ± 0.03 L{sub ⊙}, implying a hot start mass of 3–30 M{sub jup} 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.
- OSTI ID:
- 22521608
- Journal Information:
- Astrophysical Journal, Vol. 817, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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