Stars are the fundamental building blocks of our Milky Way as well as of any other galaxy. They drive the cosmic circuit of matter through nuclear synthesis, successively inject metals to the interstellar medium by means of stellar winds and supernova explosions, and affect the dynamics of the interstellar medium triggering formation of the next generation of stars. Understanding stellar physics plays a key role in order to unravel almost all phenomena in astronomy, from planetary systems to supernova explosions, from galaxy evolution to cosmology.
Research topics in the stellar astrophysics group aim at understanding hot stars in various phases of evolution, from massive main-sequence stars, helium-burning hot subdwarf stars in the Galactic disk, halo, as well as in globular clusters to white dwarfs. Close binaries play an important role in understanding the formation of many classes of star, such as the hot subdwarfs. Several binary scenarios for the formation of thermonuclear supernovae have been proposed but the progenitor systems have not been identified. Our research addresses hot subwarf/white dwarf binaries as potential single or double degenerate SN Ia progenitors. The disruption of binaries leads to the ejection of stars at unusually high speed. Since those stars are found far away from their place of birth, they are called runaway stars. Many are hot massive main-sequence stars, while others are highly evolved low mass stars The most extreme objects, the hypervelocity stars travel so fast that they leave the Galaxy. We study the kinematics of such stars from astrometry using Galactic mass models.