High-resolution spectroscopy of the transiting planet host star TrES-1

We report on a spectroscopic determination of the stellar parameters and chemical abundances for the parent star of the transiting planet TrES-1. Based on a detailed analysis of iron lines in our Keck and Hobby-Eberly Telescope spectra, we derive T-eff = 5250 +/- 75 K, log g = 4.6 +/- 0.2, and [Fe/H] = 0.00 +/- 0.09. By measuring the Ca II activity indicator and by putting useful upper limits on the Li abundance, we constrain the age of TrES-1 to be 2.5 +/- 1.5 Gyr. By comparing theoretical stellar evolution models with the observational parameters, we obtain M* = 0.89 +/- 0.05 M-. and R-* = 0.83 +/- 0.05 R-.. Our improved estimates of the stellar parameters are utilized in a new analysis of the transit photometry of TrES-1 to derive a mass M-p = (0.76 +/- 0.05) M-J, a radius R-p = 1.04(-0.05)(+0.08) R-J, and an inclination i = 89.5(-1.3)(+0.5) deg. The improved planetary mass and radius estimates provide the grounds for new crucial tests of theoretical models of evolution and evaporation of irradiated extrasolar giant planets.