Abstract

We report new spectroscopic and photometric observations of the parent stars of the recently discovered transiting planets TrES-3 and TrES-4. A detailed abundance analysis based on high-resolution spectra yields [ Fe/H] = -0.19 +/- 0.08, T-eff = 5650 +/- 75 K, and log g = 4.4 +/- 0.1 for TrES-3, and [Fe/H] = +0.14 +/- 0.09, T-eff = 6200 +/- 75 K, and log g = 4.0 +/- 0.1 for TrES-4. The accuracy of the effective temperatures is supported by a number of independent consistency checks. The spectroscopic orbital solution for TrES-3 is improved with our new radial velocity measurements of that system, as are the light-curve parameters for both systems based on newly acquired photometry for TrES-3 and a reanalysis of existing photometry for TrES-4. We have redetermined the stellar parameters taking advantage of the strong constraint provided by the light curves in the form of the normalized separation a/R-star (related to the stellar density) in conjunction with our new temperatures and metallicities. The masses and radii we derive are M-star = 0.928(-0.048)(+0.028) M-circle dot, R-star = 0.829(-0.022)(+0.015) R-circle dot, and M-star = 1.404(-0.134)(+0.066) M-circle dot, R-star = 1.846(-0.087)(+0.096) R-circle dot for TrES-3 and TrES-4, respectively. With these revised stellar parameters, we obtain improved values for the planetary masses and radii. We find M-p = 1.910(-0.080)(+0.075) M-Jup, R-p = 1.336(-0.036)(+0.031) R-Jup for TrES-3, and M-p = 0.925 +/- 0.082 M-Jup, R-p = 1.783(-0.086)(+0.093) R-Jup for TrES-4. We confirm TrES-4 as the planet with the largest radius among the currently known transiting hot Jupiters.