WASP-8b: characterization of a cool and eccentric exoplanet with Spitzer

Abstract

WASP-8b has 2.18 times Jupiter's mass and is on an eccentric ($e=0.31$) 8.16-day orbit. With a time-averaged equilibrium temperature of 948 K, it is one of the least-irradiated hot Jupiters observed with the Spitzer Space Telescope. We have analyzed six photometric light curves of WASP-8b during secondary eclipse observed in the 3.6, 4.5, and 8.0 {\microns} Infrared Array Camera bands. The eclipse depths are $0.113\pm 0.018$%, $0.069\pm 0.007$%, and $0.093\pm 0.023$%, respectively, giving respective brightness temperatures of 1552, 1131, and 938 K. We characterized the atmospheric thermal profile and composition of the planet using a line-by-line radiative transfer code and a Markov-chain Monte Carlo sampler. The data indicated no thermal inversion, independently of any assumption about chemical composition. We noted an anomalously high 3.6-{\microns} brightness temperature (1552 K); by modeling the eccentricity-caused thermal variation, we found that this temperature is plausible for radiative time scales less than $\sim 10^{2}$ hours. However, as no model spectra fit all three data points well, the temperature discrepancy remains as an open question.

Citation

(2013). WASP-8b: characterization of a cool and eccentric exoplanet with Spitzer. Astrophysical Journal, https://doi.org/10.1088/0004-637X/768/1/42

• Acceptance Date: Mar 4, 2013
• Publication Date: Apr 12, 2013
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• DOI: https://doi.org/10.1088/0004-637X/768/1/42
• Keywords: planetary systems, stars: individual (WASP-8), techniques: photometric
• Publisher URL: http://iopscience.iop.org/0004-637X/768/1/42/article?fromSearchPage=true