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

John Southworth

Published 2008-02-26Version 1

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]