Thermal Emission of Exoplanet XO-1b

TL;DR

This study measures the infrared flux ratios of exoplanet XO-1b, revealing an atmosphere with a thermal inversion layer, refining the correlation between stellar insolation and atmospheric thermal inversions in hot Jupiters.

Contribution

It provides new flux measurements at multiple wavelengths and refines the correlation between stellar insolation and thermal inversions in exoplanet atmospheres.

Findings

Flux ratios inconsistent with cloudless models

Evidence for a thermal inversion layer

Sets a new lower limit for stellar insolation causing inversions

Abstract

We estimate flux ratios of the extrasolar planet XO-1b to its host star XO-1 at 3.6, 4.5, 5.8 and 8.0 microns with the IRAC on the Spitzer Space Telescope to be 0.00086 +/- 0.00007, 0.00122 +/- 0.00009, 0.00261 +/- 0.00031 and 0.00210 +/- 0.00029, respectively. The fluxes are inconsistent with a canonical cloudless model for the thermal emission from a planet and suggest an atmosphere with a thermal inversion layer and a possible stratospheric absorber. A newly emerging correlation between the presence of a thermal inversion layer in the planetary atmosphere and stellar insolation of the planet (Burrows et al. 2007b) is refined. The sub-stellar point flux from the parent star at XO-1b of ~ 0.49 x 10^9 erg cm^-2 s^-1 sets a new lower limit for the occurrence of a thermal inversion in a planetary atmosphere.