Asteroseismology and stellar convection

Convection is an energy transfer process present in virtually every star. It operates in the cores of massive main sequence stars and the envelopes of cool stars, and determines the main sequence lifetimes of stars more massive then the Sun, it influences stellar surface abundances of chemical elements and strongly affects stellar evolution in its earliest stages. Despite the consequent importance of stellar convection for structural and evolutionary modelling, its physics are still poorly known. Any observational constraint on convection phyics is therefore essential for the understanding of stellar evolution. In this project, we want to learn about those physics by means of asteroseismology, the sounding of stellar interiors through the analysis and modelling of multiperiodically pulsating stars. This technique is similar to the determination of the Earth`s interior structure through the analysis of earthquakes. We intend to study three different types of pulsating stars whose behaviour is affected by convection. The first group are the massive (about ten times the mass of our Sun) main sequence Beta Cephei stars. They have large convective cores whose size can be determined with asteroseismic methods; this size is determined by the forces of turbulence. Some Delta Scuti stars, that are the second type of pulsator under investigation, have about twice our Sun`s mass. These are predicted to show solar-like surface oscillations caused by convective motions. We aim at detecting objects that show both types of pulsation, so we can study their interiors and exteriors with asteroseismic methods. Finally, we would also like to test the surface convection zones of a third group, pulsating white dwarf stars that have much larger surface gravities than the other pulsators under consideration. We expect that this project will lead to a considerably better understanding of stellar core and surface convection, which can then be directly implemented in models of stellar structure and evolution. In addition, we expect to obtain generally applicable information about interior rotation profiles and the structure of pre-supernovae and thus would be able to constrain the chemical evolution of galaxies tighter. In the end, we should be able to model stellar structure and evolution with much higher confidence than possible today.

Convection is an energy transfer process present in virtually every star. It operates in the cores of massive main sequence stars and the envelopes of cool stars, and determines the main sequence lifetimes of stars more massive then the Sun, it influences stellar surface abundances of chemical elements and strongly affects stellar evolution in its earliest stages. Despite the consequent importance of stellar convection for structural and evolutionary modelling, its physics are still poorly known. Any observational constraint on convection phyics is therefore essential for the understanding of stellar evolution. In this project, we want to learn about those physics by means of asteroseismology, the sounding of stellar interiors through the analysis and modelling of multiperiodically pulsating stars. This technique is similar to the determination of the Earth`s interior structure through the analysis of earthquakes. We intend to study three different types of pulsating stars whose behaviour is affected by convection. The first group are the massive (about ten times the mass of our Sun) main sequence Beta Cephei stars. They have large convective cores whose size can be determined with asteroseismic methods; this size is determined by the forces of turbulence. Some Delta Scuti stars, that are the second type of pulsator under investigation, have about twice our Sun`s mass. These are predicted to show solar-like surface oscillations caused by convective motions. We aim at detecting objects that show both types of pulsation, so we can study their interiors and exteriors with asteroseismic methods. Finally, we would also like to test the surface convection zones of a third group, pulsating white dwarf stars that have much larger surface gravities than the other pulsators under consideration. We expect that this project will lead to a considerably better understanding of stellar core and surface convection, which can then be directly implemented in models of stellar structure and evolution. In addition, we expect to obtain generally applicable information about interior rotation profiles and the structure of pre-supernovae and thus would be able to constrain the chemical evolution of galaxies tighter. In the end, we should be able to model stellar structure and evolution with much higher confidence than possible today.