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