Thermal emission at 3.6-8 micron from WASP-19b: a hot Jupiter without a stratosphere orbiting an active star

TL;DR

This study detects thermal emission from exoplanet WASP-19b across multiple infrared wavelengths, revealing a non-inverted atmosphere likely influenced by its active host star, and provides insights into its atmospheric composition.

Contribution

First to combine Spitzer IRAC observations with previous data to characterize WASP-19b's atmosphere and link star activity to the absence of a temperature inversion.

Findings

WASP-19b's atmosphere lacks a strong temperature inversion.

Active host star likely suppresses atmospheric inversions.

Data inconclusive on atmospheric carbon-to-oxygen ratio.

Abstract

We report detection of thermal emission from the exoplanet WASP-19b at 3.6, 4.5, 5.8 and 8.0 micron. 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 micron to construct a spectral energy distribution of the planet's dayside atmosphere. By comparing this with model-atmosphere spectra, we find that the dayside atmosphere of WASP-19b lacks a strong temperature inversion. As WASP-19 is an active star (log RHK = -4.50 +/- 0.03), this finding supports the hypothesis of Knutson, Howard & Isaacson (2010) that inversions are suppressed in hot Jupiters orbiting active stars. The available data are unable to differentiate between a carbon-rich and an oxygen-rich atmosphere.