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

The characterization of the growing number of newly discovered exoplanets ---nature, internal structure, formation and evolution--- strongly relies on the properties of their host-star, i.e. its mass, radius and age. These latter 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 the transit analysis. Additional constraints for the models can be provided by asteroseismic observations of the host-star. The precision and accuracy on 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 are still based on a number of approximations, they rely on physical inputs and data that can be uncertain and do not treat correctly 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 errors ---observational or theoretical--- that intervene in the age determination based on stellar models.