Secondary Eclipse Photometry of the Exoplanet WASP-5b with Warm Spitzer

TL;DR

This study uses Spitzer Space Telescope data to analyze the secondary eclipse of exoplanet WASP-5b, providing insights into its atmospheric properties and confirming a likely circular orbit.

Contribution

First infrared secondary eclipse measurements of WASP-5b with constraints on its atmospheric temperature profile and orbital eccentricity.

Findings

Measured eclipse depths at 3.6 and 4.5 microns.

Evidence for a hot dayside atmosphere with possible thermal inversion.

Orbit consistent with being circular, no timing variations observed.

Abstract

We present photometry of the extrasolar planet WASP-5b in the 3.6 and 4.5 micron bands taken with the Spitzer Space Telescope's Infrared Array Camera as part of the extended warm mission. By examining the depth of the planet's secondary eclipse at these two wavelengths, we can place joint constraints on the planet's atmospheric pressure-temperature profile and chemistry. We measure secondary eclipse depths of 0.197% +/- 0.028% and 0.227% +/- 0.025% in the 3.6 micron and 4.5 micron bands, respectively. Our observations are best matched by models showing a hot dayside and, depending on our choice of model, a weak thermal inversion or no inversion at all. We measure a mean offset from the predicted center of eclipse of 0.078 +/- 0.032 hours, translating to ecos(omega) = 0.0031 +/- 0.0013 and consistent with a circular orbit. We see no evidence for any eclipse timing variations comparable to those reported in a previous transit study.