The ROSAT X-ray and EUV sky survey revealed that most H-rich white dwarfs hotter than 40,000K contain significant quantities of heavy elements in their atmospheres. However, the ROSAT data are unable to say anything about the role of helium in the hottest white dwarfs. Spectroscopic observations with the Extreme Ultraviolet Explorer allow us to perform a direct and sensitive search for Hell absorption features in DA white dwarfs. In almost all cases no trace of He is found but G191-B2B and HZ43 do appear to have photospheric He, which is an important result for our views of the evolutionary relationships between H and He-rich groups of white dwarfs. Early studies of H deficient white dwarfs with EUVE encounter difficulties in interpreting the spectra, showing that even more detail, in the form of additional opacity sources, needs to be included in our state-of-the-art model atmospheres.
All Science Journal Classification (ASJC) codes
- Aerospace Engineering
- Astronomy and Astrophysics
- Atmospheric Science
- Space and Planetary Science
- Earth and Planetary Sciences(all)