DEPARTEMENT 3: Astrophysics

Research theme: Hot stars

Hot stars have an important role in the ecology and evolution of our Galaxy and that of other galaxies. These stars not only have a high surface temperature, but they are also the most massive and most luminous stars. Due to their high luminosity, radiation pressure blows away their outer layers. The material streams away from the star in what is called a stellar wind and reaches speeds up to 3000 km/s. Due to the stellar wind the star loses some 10^-6 to 10^-5 solar masses per year. Furthermore, some hot stars rotate so fast that they form a disk around their equator and lose mass in that way.

Nuclear reactions in the core of these hot stars transform hydrogen into other chemical elements. Due to the mass loss, this enriched material is pumped into the interstellar medium. At a later stage, new stars are born out of this enriched interstellar medium. Hot stars are thus an important ingredient in the evolutionary cycle of their galaxy.

We study the atmosphere and stellar wind of hot stars, both observationally and theoretically. The observations are done mainly at millimetre and centimetre radio wavelengths. On the theoretical side, we model the atmosphere, stellar wind and the disk, using both hydrodynamics and radiative transfer models.

Hot stars are also research objects for asteroseismology. In this field of astrophysics, we try to learn more about the internal structure of stars by making detailed studies of stellar pulsations, based on time series of both photometric and spectroscopic observations, mainly at optical wavelengths. The observed pulsation frequencies are highly dependent on the star's internal structure and the processes occurring there. Such an asteroseismological study requires a period analysis (finding out what periodical changes are present in the measurements) and a mode identification (determining what type of pulsation causes each pulsation period), before we can start with theoretical modelling.