Hot Stars: Old-Fashioned or Trendy?
Spectroscopic analyses with the intention of the interpretation of the UV-spectra of the brightest stars as individuals - supernovae - or as components of star-forming regions - massive O stars - provide a powerful tool with great astrophysical potential for the determination of extragalactic distances and of the chemical composition of star-forming galaxies even at high redshifts. The perspectives of already initiated work with the new generation of tools for quantitative UV-spectroscopy of Hot Stars that have been developed during the last two decades are presented and the status of the continuing effort to construct corresponding models for Hot Star atmospheres is reviewed. Because the physics of the atmospheres of Hot Stars are strongly affected by velocity expansion dominating the spectra at all wavelength ranges, hydrodynamic model atmospheres for O-type stars and explosion models for Supernovae of Type Ia are necessary as basis for the synthesis and analysis of the spectra. It is shown that stellar parameters, abundances and stellar wind properties can be determined by the methods of spectral diagnostics already developed. Additionally, it will be demonstrated that models and synthetic spectra of Type Ia Supernovae of required quality are already available that make it possible to tackle the question of whether Supernovae Ia are standard candles in a cosmological sense and the SN-luminosity distances thus indicate accelerated expansion of the universe.