Thermal emission at 3.6-8 μm from WASP-19b: A hot jupiter without a stratosphere orbiting an active star

Abstract

We report detection of thermal emission from the exoplanet WASP-19b at 3.6, 4.5, 5.8 and 8.0 μm. We used the InfraRed Array Camera on the Spitzer Space Telescope to observe two occultations of WASP-19b by its host star. We combine our new detections with previous measurements of WASP-19b's emission at 1.6 and 2.09 μm to construct a spectral energy distribution ofthe planet's dayside atmosphere. By comparing this with model-atmosphere spectra, we find thatthe dayside atmosphere ofWASP-19b lacks a strong temperature inversion. As WASP-19 is an active star (log R'HK =-4.50 ± 0.03), this finding supports the hypothesis of Knutson, Howard and Isaacson that inversions are suppressed in hot Jupiters orbiting active stars. The available dataare unable to differentiate between a carbon-rich and an oxygen-rich atmosphere. © 2013 TheAuthor. Published by Oxford University Press on behalf of the Royal Astronomical Society.