Analysis of Kepler's short-cadence photometry for TrES-2b

TL;DR

This paper analyzes high-precision Kepler short-cadence data of TrES-2b to refine its system parameters, measure its low albedo, and perform detailed transit timing analysis with implications for additional bodies.

Contribution

It provides the most accurate transit parameters for TrES-2b, introduces a novel control data method for phase effects, and sets stringent limits on additional planets and moons.

Findings

TrES-2b has the lowest geometric albedo among exoplanets, Ag<0.146.

Transit timing precision reaches a few seconds, enabling detection of perturbations.

No evidence found for short-period TTVs or additional transiting bodies.

Abstract

We present an analysis of 18 short-cadence (SC) transit lightcurves of TrES-2b using quarter 0 (Q0) and quarter 1 (Q1) from the Kepler Mission. The photometry is of unprecedented precision, 237ppm per minute, allowing for the most accurate determination of the transit parameters yet obtained for this system. Global fits of the transit photometry, radial velocities and known transit times are used to obtain a self-consistent set of refined parameters for this system, including updated stellar and planetary parameters. Special attention is paid to fitting for limb darkening and eccentricity. We place an upper limit on the occultation depth to be <72.9ppm to 3-sigma confidence, indicating TrES-2b has the lowest determined geometric albedo for an exoplanet, of Ag<0.146. We also produce a transit timing analysis using Kepler's short-cadence data and demonstrate exceptional timing precision at the level of a few seconds for each transit event. With 18 fully-sampled transits at such high precision, we are able to produce stringent constraints on the presence of perturbing planets, Trojans and extrasolar moons. We introduce the novel use of control data to identify phasing effects. We also exclude the previously proposed hypotheses of short-period TTV and additional transits but find the hypothesis of long-term inclination change is neither supported nor refuted by our analysis.