Physics and Astronomy
planets, satellites, atmospheres, stars
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. (2013) 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 LEECH exoplanet imaging survey. By compar-ing our new photometry and literature photometry to 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 follow-ing parameters: Teff =544±10 K, g/s2, [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 L⊙, im-plying 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 super-stellar metallicity. Since planet formation can create objects with non-stellar metal-licities, while binary star formation cannot, this result suggests that GJ 504 b formed like a planet, not like a binary companion.
Source Publication Title
American Astronomical Society
Skemer, Andrew J.; Morley, Caroline V.; Zimmerman, Neil T.; Skrutskie, Michael F.; Leisenring, Jarron; Buenzli, Esther; Bonnefoy, Mickael; Bailey, Vanessa; Hinz, Philip; Defrere, Denis; Esposito, Simone; Apai, Daniel; Biller, Beth; Brandner, Wolfgang; Close, Laird; Crepp, Justin R.; De Rosa, Robert J.; Desidera, Silvano; Eisner, Josh; Fortney, Jonathan; Freedman, Richard; Henning, Thomas; Hofmann, Karl-Heinz; Kopytova, Taisiya; Lupu, Roxana; Maire, Anne-Lise; Males, Jared R.; Marley, Mark; Morzinski, Katie; Oza, Apurva; Patience, Jenny; Rajan, Abhijith; Rieke, George; Schertl, Dieter; Schlieder, Joshua; Stone, Jordan; Su, Kate; Vaz, Amali; Visscher, Channon; Ward-Duong, Kimberly; Weigelt, Gerd; and Woodward, Charles E., "LEECH Exoplanet Imaging Survey: Characterization of the Coldest Directly Imaged Exoplanet, GJ 504 b, and Evidence for Super-Stellar Metallicity" (2016). Faculty Work: Comprehensive List. 485.