A Uniform Search for Secondary Eclipses of Hot Jupiters in Kepler Q2 Light Curves
Abstract
In this paper, we present the results of searching the Kepler Q2 public data set for the secondary eclipses of 76 hot Jupiter planet candidates from the list of 1235 candidates published by Borucki et al. This search has been performed by modeling both the Kepler presearch data conditioned light curves and new light curves produced via our own photometric pipeline. We derive new stellar and planetary parameters for each system, while calculating robust errors for both. We find 16 systems with 1σ2σ, 14 systems with 2σ3σ, and 6 systems with >3σ confidence level secondary eclipse detections in at least one light curve produced via the Kepler presearch data conditioned light curve or our own pipeline; however, results can vary depending on the light curve modeled and whether eccentricity is allowed to vary or not. We estimate false alarm probabilities of 31%, 10%, and 6% for the 1σ2σ, 2σ3σ, and >3σ confidence intervals, respectively. Comparing each secondary eclipse result to theoretical expectations, we find that the majority of detected planet candidates emit more light than expected owing to thermal blackbody emission in the optical Kepler bandpass, and present a trend of increasing excess emission with decreasing maximum effective planetary temperature. These results agree with previously published optical secondary eclipse data for other hot Jupiters. We explore modeling biases, significant planetary albedos, nonlocal thermodynamic equilibrium or other thermal emission, significant internal energy generation, and misidentification of brown dwarfs, lowmass stars, or stellar blends as possible causes of both the excess emission and its correlation with expected planetary temperature. Although we find that 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, are able to explain most of the systems. Identifying systems that we deem likely to be lowmass stars or stellar blends, we estimate an 11% falsepositive rate in the current Kepler planet candidate sample of hot Jupiters. We also establish robust upper limits on the eclipse depth for the remaining systems and find that the emission of a significant fraction of these systems is consistent with the planets having very low albedos, i.e., at least 30% of all systems have A_{g} < 0.3 at 1σ confidence levels. This result augments the current number of constrained exoplanetary albedos and extends the sample of low albedo determinations to planets with temperatures as low as 1200 K. Finally, we note that continued observations with the Kepler spacecraft and improved techniques for the removal of systematic noise in the Kepler data are needed to better characterize these systems.
 Publication:

The Astronomical Journal
 Pub Date:
 February 2012
 DOI:
 10.1088/00046256/143/2/39
 arXiv:
 arXiv:1112.1021
 Bibcode:
 2012AJ....143...39C
 Keywords:

 methods: data analysis;
 planetary systems;
 techniques: photometric;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 33 pages, 9 figures, 3 tables. Submitted to the Astronomical Journal 9/13/2011. Accepted 12/4/2011