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.. 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.