Convection and Pulsation in F- and G-type Stars

Space missions such as TESS have allowed the discovery of many new planets outside our solar system. To characterise these exoplanets as accurately as possible it is required to know the basic properties of those stars which they orbit. Only with the precise knowledge of radius, mass, and age of a star it is possible to derive those essential physical parameters also for their planets. Their measurement is thus one of the main goals of the PLATO mission of ESA which will be launched by the end of 2026. One of the most important technologies for this purpose is asteroseismology. It permits to determine the mass and the radius of a star to within a few percent but also to derive its age to within better than 10% from measurements of the variations in brightness and radius of solar-like stars of spectral type G or somewhat more massive and brighter main sequence stars of spectral type F, such as the star Procyon. PLATO is designed to allow finding a planet with earth-like values for mass and radius which orbits inside the so-called habitable zone and which could hence support terrestrial forms of life, around a star comparable to the Sun in terms of age, mass, and diameter. Since the age of a star cannot be directly measured, accurate models of the interior structure of stars are necessary. In this context the quantitative description of convection poses the greatest among the various challenges. The mixing and the heat transport by the rise of hot plasma which is lighter than its environment into cooler regions followed by the sinking of plasma which has become heavier and cooler than its environment influences the depth dependence of the speed of sound within a star. Therefore, convection models are important to asteroseismology for the interpretation of measurements and vice versa they have to be tested as profoundly as possible before they are used. This is also achieved through testing them with three dimensional numerical simulations of regions within a star. These are based on mathematical methods and physical models that are also used in weather forecast. Thus, in this project investigations will be made on how frequencies and amplitudes of brightness variations, which are typical for solar-like stars, are influenced by the interaction of convection and pulsation and the role of magnetic fields in these processes will be studied, too. Therefore, new convection models will be developed and analysed which are expected to allow much more accurate predictions and which might also be applied within meteorology later on. For testing these ideas new numerical simulations performed on supercomputers and based on methods from numerical hydrodynamics are necessary. For carrying them out efficiently new mathematical methods have to be implemented into the ANTARES code which has been developed in Vienna. These will provide new insights into the non-local nature of convection and its influence on pulsation, temperature stratification, and mixing in stars.