Mysterious Atmospheres of Cool White Dwarfs
Piotr Kowalski
German Research Centre for Geosciences Helmholtz Centre Potsdam, Germany

Cool white dwarfs are the remnants of the oldest stars that existed in our Galaxy. Being billions of years old they can be used for dating old stellar populations, the investigation of stars formation history and derivation of internal composition of rocky exoplanets. The difficulties in obtaining a reliable description of the physicochemical processes prevailing in the extreme, fluid-like atmospheres of these stars limit the full usage of white dwarfs for such purposes. In our work we study the properties of condensed hydrogen and helium rich matter that constitutes the atmospheres of these stars. The research is performed by application of modern computational methods of materials science and quantum chemistry. Our goal is to derive the reliable white dwarf atmosphere models, which could be used for an in-depth analysis of the rapidly growing data on cool white dwarfs. Such models will allow for precise and definitive determination of the surface properties of these stars. We will show the results of our recent studies of near-IR spectra of cool, carbon-rich white dwarfs that independently support our recent finding that the DQp stars are the DQ stars with pressure-shifted Swan bands of C2. We will also show the UV spectra of selected cool white dwarfs, indicating that the majority of the stars with Teff<5000 K have hydrogen-rich atmospheres. Last but not least we will discuss the remaining problems of the models in describing the near-IR and IR spectra of very cool white dwarfs

Date:	Jeudi, 28 juin 2012
Time:	11:30
Where:	Université de Montréal
	Université de Montréal, Pavillon Roger-Gaudry, local D-460
Contact:	Pierre Bergeron