A Uniform Search for Secondary Eclipses of Hot Jupiters in Kepler Q2 Lightcurves

TL;DR

This study searches Kepler Q2 data for secondary eclipses of 76 hot Jupiters, finding several with excess emission likely due to planetary albedos and thermal effects, and provides new planetary parameters and upper limits.

Contribution

It presents a comprehensive search for secondary eclipses in Kepler data, introduces new light curves and parameters, and analyzes planetary albedos and emission trends with temperature.

Findings

16 systems with 1-2 sigma detections of secondary eclipses

Most detected planets emit more light than expected from blackbody models

Significant planetary albedos increase with decreasing atmospheric temperature

Abstract

We present the results of searching the Kepler Q2 public dataset for the secondary eclipses of 76 hot Jupiter planet candidates from the list of 1,235 candidates published by Borucki et al. (2011). This search has been performed by modeling both the Kepler PDC light curves and new light curves produced via our own photometric pipeline. We derive new stellar and planetary parameters for each system with robust errors. We find 16 systems with 1-2 sigma, 14 systems with 2-3 sigma, and 6 systems with >3 sigma confidence level secondary eclipse detections in at least one light curve. We find that the majority of detected planet candidates emit more light than expected due to thermal blackbody emission in the optical Kepler bandpass, and present a trend of increasing excess emission with decreasing maximum effective planetary temperature. We explore modeling biases, significant planetary albedos, non-LTE or other thermal emission, significant internal energy generation, and exoplanet mis-identification as possible causes of both the excess emission and its correlation with expected planetary temperature. Although we find no single cause is able to explain all of the planet candidates, significant planetary albedos, with a general trend of increasing planetary albedos with decreasing atmospheric temperatures, is able to explain most of the systems. We estimate an 11% false positive rate in the current Kepler planet candidate sample of hot Jupiters. We also establish robust upper limits on the eclipse depth for all systems, and find that a significant fraction of these systems have very low albedos, significantly augmenting and extending the sample of albedo determinations to planets as cool as 1200 K. Finally, we note that continued observations with Kepler, and improved techniques for the removal of systematic noise in the Kepler data, are needed to better characterize these systems.