A ccepted forpublication in The A strophysicalJournal D etection of T herm alE m ission of X O -2b: E vidence for a W eak Tem perature Inversion

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 μm with Infrared Array Camera 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 × 109 erg cm−2 s−1 lies in the predicted transition region between atmospheres with and without upper atmospheric temperature inversion.

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