Winds and Disks around Stars

The different physical processes occuring within astronomical objects are related to large variations in the physical time scales, e.g. to cover stellar evolution the system of equations has to be integrated over billions of sound crossing times. Being interested on the long-term evolution we have to deal with sophisticated numerical methods, which are able to follow the evolution over a long time interval. Such methods are called implicit and require complicated program structures. To ensure the spatial resolution an adaptive grid will be developed in the proposed project, which is applied on two-dimensional radiating flows with self-gravity in axial symmetry. Due to the flexibilty of the proposed approach a number of astrophysical applications seem possible and in the next three years we concentrate the simulations on winds and disks around stars. First, the pulsations of rotating stars will be investigated because a large number of asteroseismological data is becoming available for a more detailed understanding of such objects. The mixing of elements by rotationally induced mass currents provides another possibility of such implicit methods, and a different chemical structure alters the further evolution of a rotating star. Both processes, pulsation as well as mixing within the star influence also the properties of mass loss by a stellar wind. As observed and shown by earlier investigations rotation modifies the stellar wind, in particular in the case of evolved and extended cool stars. In such stellar atmospheres dust particles can be formed by condensation out of the gas phase and these dust grains can effectively absorb the stellar light. The process of dust formation depends strongly on the temperature and density stratification in the condensation region and therefore rotation leads to a pole-equator variation which can be observed later in the shaping of Planetary Nebulae. A third application is centered on the formation and evolution of protostellar disks which are closely related to the question of planet formation. The growing number of newly discovered extra-solar, jupiter-like planets in orbits near to the central objects make such theoretical long-term studies important because the evolution of dust particles, the transport of angular momentum and their connection to planet formation can only be handled by such implicit numerical simulations.