Secondary eclipse observations for seven hot-Jupiters from the Anglo-Australian Telescope

Abstract

We report detections and constraints for the near-infrared Ks band secondary eclipses of seven hot-Jupiters using the IRIS2 infrared camera on the Anglo-Australian Telescope. Eclipses in the Ks band for WASP-18b and WASP-36b have been measured for the first time. We also present new measurements for the eclipses ofWASP-4b, WASP-5b, andWASP-46b, as well as upper limits for the eclipse depths ofWASP-2b andWASP-76b. In particular, two full eclipses ofWASP-46b were observed, allowing us to demonstrate the repeatability of our observations via independent analyses on each eclipse. Significant numbers of eclipse depths for hot-Jupiters have now been measured in both Ks and the four Spitzer IRAC bandpasses. We discuss these measurements in the context of the broad-band colours and brightness temperatures of the hot-Jupiter atmosphere distribution. Specifically, we re-examine the proposed temperature dichotomy between the most irradiated, and mildly irradiated planets. We find no evidence for multiple clusters in the brightness temperature-equilibrium temperature distributions in any of these bandpasses, suggesting a continuous distribution of heat re-emission and circulation characteristics for these planets.