We report on a spectroscopic determination of the atmospheric parameters and chemical abundance of the parent star of the recently discovered transiting planet TrES-2. A detailed LTE analysis of a set of Fe I and Fe II lines from our Keck spectra yields Teff = 5850 ±50 K, log g = 4.4 ±0.1, and [Fe/H] = -0.15 ±0.10. Several independent checks (e.g., additional spectroscopy, line-depth ratios) confirm the reliability of our spectroscopic Teff estimate. The mass and radius of the star, needed to determine the properties of the planet, are traditionally inferred by comparison with stellar evolution models using Teff and some measure of the stellar luminosity, such as the spectroscopic surface gravity. We apply here a new method in which we use instead of log g the normalized separation a/R* (related to the stellar density), directly measurabele from the light curves of transiting planets with much greater precision. With the a/R* value from the light-curve analysis of Holman and coworkers and our Teff estimate, we obtain M* = 0.980 ± 0.062 M⊙ and R* = 1.000+0036/-0.033 R⊙, and an evolutionary age of 5.1+23/-2.3 Gyr, in good agreement with other constraints (Ca II H and K line cores, lithium abundance, and rotation). The new stellar parameters yield improved values for the planetary mass and radius of Mp = 1.198 ±0.053 M3 and Rp = 1.220+0.045/-0.042 Rj, confirming that TrES-2 is the most massive among the currently known nearby (dp≳300pc) transiting hot Jupiters. The surface gravity of the planet, log gp = 3.299 ±0.016, can be derived independently of the knowledge of the stellar parameters (i.e., directly from observations), and with a very high precision rivaling that of the best known double-lined eclipsing binaries.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- Planetary systems
- Stars: abundances
- Stars: fundamental parameters
- Stars: individual (TrES-2)