2013ApJ...768...42C

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 µm Infrared Array Camera bands. The eclipse depths are 0.113%±0.018%, 0.069%±0.007%, and 0.093%±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 µm brightness temperature (1552 K); by modeling the eccentricity-caused thermal variation, we found that this temperature is plausible for radiative timescales less than ∼10² hr. However, as no model spectra fit all three data points well, the temperature discrepancy remains as an open question.