Document Type
Article
Publication Date
2-2016
Department
Physics and Astronomy
Keywords
planets, satellites, atmospheres, stars
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. (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
Astrophysical Journal
Publisher
American Astronomical Society
Volume
817
Issue
2
First Page
166
Recommended Citation
Skemer, A. J., Morley, C. V., Zimmerman, N. T., Skrutskie, M. F., Leisenring, J., Buenzli, E., Bonnefoy, M., Bailey, V., Hinz, P., Defrere, D., Esposito, S., Apai, D., Biller, B., Brandner, W., Close, L., Crepp, J. R., De Rosa, R. J., Desidera, S., Eisner, J., Fortney, J., Freedman, R., Henning, T., Hofmann, K., Kopytova, T., Lupu, R., Maire, A., Males, J. R., Marley, M., Morzinski, K., Oza, A., Patience, J., Rajan, A., Rieke, G., Schertl, D., Schlieder, J., Stone, J., Su, K., Vaz, A., Visscher, C., Ward-Duong, K., Weigelt, G., & Woodward, C. E. (2016). LEECH Exoplanet Imaging Survey: Characterization of the Coldest Directly Imaged Exoplanet, GJ 504 b, and Evidence for Super-Stellar Metallicity. Astrophysical Journal, 817 (2), 166. Retrieved from https://digitalcollections.dordt.edu/faculty_work/485
Comments
Copyright © Astrophysical Journal 2016