Homogeneous studies of transiting extrasolar planets. I. Light curve analyses

TL;DR

This study provides a homogeneous analysis of 14 transiting exoplanet light curves, highlighting the importance of limb darkening treatment, revealing discrepancies in radius ratios, and confirming a correlation between planetary surface gravity and orbital period.

Contribution

It introduces a consistent methodology for analyzing transit light curves, compares different limb darkening laws, and discusses the impact of systematic errors on parameter uncertainties.

Findings

Limb darkening coefficients significantly affect parameter uncertainties.

Discrepancies exist between different light curve analyses for the same planets.

Systematic errors in light curves can dominate over analysis methods.

Abstract

I present an homogeneous analysis of the transit light curves of 14 well-observed transiting extrasolar planets. The light curves are modelled using JKTEBOP, random errors are measured using Monte Carlo simulations, and the effects of correlated noise are included using a residual-permutation algorithm. The importance of stellar limb darkening (LD) on the light curve solutions and parameter uncertainties is investigated using five different LD laws. The linear LD law cannot adequately fit the HST photometry of HD 209458, but the other four laws give very similar results to each other. In most cases fixing the LD coefficients at theoretical values does not bias the results, but DOES cause the error estimates to be too small. The available theoretical LD coefficients clearly disagree with empirical values measured from the HST light curves of HD 209458; LD must be included as fitted parameters when analysing high-quality light curves. In most cases the results of my analysis agree with the values found by other authors, but the uncertainties I find are up to 3 times larger. Despite this, the analyses of sets of independent light curves for both HD 189733 and HD 209458 do not agree with each other. This discrepancy is worst for the ratio of the radii (6.7 and 3.7 sigma), which depends primarily on the depth of the transit. It is therefore not due to the analysis method but is present in the light curves. These underlying systematic errors cannot be detected from the reduced data alone. Using my results and the stellar spectroscopic orbits, I confirm the correlation between the surface gravities of transiting extrasolar planets and their orbital periods. [abridged]