The Photoeccentric Effect and Proto-Hot Jupiters I. Measuring photometric eccentricities of individual transiting planets

TL;DR

This paper introduces a Bayesian method to measure the eccentricity of transiting exoplanets from their light curves alone, enabling the identification of eccentric proto-hot Jupiters without radial velocity data.

Contribution

The authors develop and validate a novel photometric technique to determine individual exoplanet eccentricities solely from transit light curves, bypassing the need for radial velocity measurements.

Findings

Successfully measured HD 17156 b's eccentricity from light curve data.

Demonstrated the method's viability with Kepler data.

Identified the potential to find eccentric proto-hot Jupiters efficiently.

Abstract

Exoplanet orbital eccentricities offer valuable clues about the history of planetary systems. Eccentric, Jupiter-sized planets are particularly interesting: they may link the "cold" Jupiters beyond the ice line to close-in hot Jupiters, which are unlikely to have formed in situ. To date, eccentricities of individual transiting planets primarily come from radial velocity measurements. Kepler has discovered hundreds of transiting Jupiters spanning a range of periods, but the faintness of the host stars precludes radial velocity follow-up of most. Here we demonstrate a Bayesian method of measuring an individual planet's eccentricity solely from its transit light curve using prior knowledge of its host star's density. We show that eccentric Jupiters are readily identified by their short ingress/egress/total transit durations -- part of the "photoeccentric" light curve signature of a planet's eccentricity --- even with long-cadence Kepler photometry and loosely-constrained stellar parameters. A Markov Chain Monte Carlo exploration of parameter posteriors naturally marginalizes over the periapse angle and automatically accounts for the transit probability. To demonstrate, we use three published transit light curves of HD 17156 b to measure an eccentricity of e = 0.71 +0.16/-0.09, in good agreement with the discovery value e = 0.67+/-0.08 based on 33 radial-velocity measurements. We present two additional tests using actual Kepler data. In each case the technique proves to be a viable method of measuring exoplanet eccentricities and their confidence intervals. Finally, we argue that this method is the most efficient, effective means of identifying the extremely eccentric, proto hot Jupiters predicted by Socrates et al. (2012).