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, 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