Detection of Thermal Emission of XO-2b: Evidence for a Weak Temperature Inversion

TL;DR

This study measures infrared flux ratios of exoplanet XO-2b, providing tentative evidence for a weak temperature inversion in its atmosphere, which is consistent with models predicting a transition region for atmospheric temperature profiles.

Contribution

First infrared flux measurements of XO-2b indicating a possible weak temperature inversion in its atmosphere.

Findings

Flux ratios at multiple wavelengths measured with Spitzer IRAC.

Evidence suggests a weak temperature inversion in XO-2b's atmosphere.

XO-2b's substellar flux is in the predicted transition zone for atmospheric inversion.

Abstract

We estimate flux ratios of the extrasolar planet XO-2b to its host star XO-2 at 3.6, 4.5, 5.8 and 8.0 micron with IRAC on the Spitzer Space Telescope to be 0.00081 +- 0.00017, 0.00098 +- 0.00020, 0.00167 +- 0.00036 and 0.00133 +- 0.00049, respectively. The fluxes provide tentative evidence for a weak temperature inversion in the upper atmosphere, the precise nature of which would need to be confirmed by longer wavelength observations. XO-2b substellar flux of 0.76 x 10^9 ergs cm^-2 s^-1 lies in the predicted transition region between atmospheres with and without upper atmospheric temperature inversion.