2004ApJ...616L.167S

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, logg=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±0.05M_J, a radius R_p=1.04^+0.08_–0.05R_J, and an inclination i=89.5^+0.5_–1.3deg. 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.