Hot Stars cover sub-groups of objects in different parts of the HR diagram and at different evolutionary stages. The most important sub-groups are massive O/B Stars, Central Stars of Planetary Nebulae, and Supernovae. All these objects have in common that they are characterized by high radiation energy densities and expanding atmospheres. Due to these properties, the state of the outermost parts of these objects is characterized by non-equilibrium thermodynamics and radiation hydrodynamics.
The USM Hot Star group is experienced in the corresponding theory of stellar atmospheres, and in model simulations and the computation of realistic synthetic spectra for these astrophysically important objects.
Specific topics address the relevance of Hot Stars for current astronomical research:
- The present cosmological question of the reionization of the universe requires quantitative predictions about the influence of very massive, extremely metal-poor Population III stars on their galactic and intergalactic environment. The objective is to deduce the ionization efficiency of a Top-heavy IMF via realistic spectral energy distributions of these very massive stars.
- Due to the impact of massive stars on their environment the underlying physics for the spectral appearance of starburst galaxies are rooted in the atmospheric expansion of massive O stars which dominate the UV wavelength range in star-forming galaxies. Therefore, the UV-spectral features of massive O stars can be used as tracers of age and chemical composition of starburst galaxies even at high redshift
- Distant SNe Ia appear fainter than standard candles in an empty Friedmann model of the universe. This surprising result requires investigating the role of Supernovae of Type Ia as distance indicators with respect to diagnostic issues of their spectra
Research fields for which PhD projects are offered:
- Diagnostics of UV and optical spectra of O type stars
- Synthetic spectra of the x-ray range of O type stars
- IR-spectroscopy of massive stars
- Clumping in hot star winds - constraints from a multi-wavelength analysis
The main focus of the working group thus is to develop diagnostic techniques in order to extract the complete physical stellar information from the spectra at all wavelength ranges.
For more details visit our homepage
USM Stellar Astrophysics - Expanding Atmospheres of Hot Stars.