Ages of Exoplanet Host-stars from Asteroseismology: HD 17156, a Case Study

The characterization of the growing number of newly discovered exo-planets - nature, internal structure, formation and evolution-strongly relies on the properties of their host-star, i.e., its mass, radius and age. These can be inferred from stellar evolution models constrained by the observed global parameters of the host-star - effective temperature, photospheric chemical composition, surface gravity and/or luminosity and by its mean density inferred from a transit analysis. Additional constraints for the models can be provided by asteroseismic observations of the host-star. The precision and accuracy of the age, mass and radius not only depend on the quality and number of available observations of the host-star but also on our ability to model it properly. Stellar models arc still based on a number of approximations, they rely on physical inputs and data that can be uncertain and do not correctly treat all the physical processes that can be at work inside a star. We focus here on the determination of the age of HD 17156, an oscillating star hosting an exoplanet. We examine the dispersion of the age values obtained by different methods-empirical or model-dependent-and the different sources of error-observational or theoretical-that intervene in the age determination based on stellar models.