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 = M_J, a radius R_p = 1.04R_J, and an inclination i = 89.5 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.