Mg line profiles for cool WD and their application in the UV

Since last decade there have been great advances and extremely exciting results in the search and interpretation for cool DZ white dwarfs. In the formation of their spectra, the far wings of alkaline earth metals like Ca and Mg, play an extraordinary role. We present theoretical profiles of theMg resonance lines perturbed by He at the extreme density conditions found in the cool atmosphere of DZ white dwarfs. Atmosphere models are necessary to calculate synthetic spectra and to derive reliable parameters and the atmospheric composition for such objects. We present synthetic spectra tracing the behavior of the Mg resonance line profiles under the low temperatures and high gas pressures prevalent in the cool atmospheres of DZ white dwarfs.