The Transit Light Curve Project. III. Tres Transits of TrES-1

We present z-band photometry of three consecutive transits of the exoplanet TrES-1, with an accuracy of 0.15% and a cadence of 40 s. We improve on estimates of the system parameters, finding in particular that the planetary radius is 1.081+/-0.029 R_Jup and the stellar radius is 0.811+/-0.020 R_solar. The uncertainties include both the statistical error and the systematic error arising from the uncertainty in the stellar mass. The transit times are determined to within about 15 s and allow us to refine the estimate of the mean orbital period: P=3.0300737+/-0.0000026 days. We find no evidence for starspots or other irregularities that have been previously reported.