Contributed Talk - Splinter HotStars
Spectral analysis of hot DA- and DAO-type white dwarfs
Semih Filiz, Thomas Rauch, Klaus Werner
Karls Eberhard Universität Tübingen
We aim to understand the spectral evolution of a small subgroup of H-rich WDs, the so-called hybrid (or DAO) WDs which exhibit both, H and He lines in their spectra. Though small in number, they represent an evolutionary phase run through by the majority (≈ 75%) of all WDs. We started a NLTE analysis of UV and optical spectra of 36 hot (Teff > 60000K) WDs which allows, together with distances precisely measured by Gaia, to locate them in the HRD and to derive their stellar parameters (M, R, L). We measure metal abundances to shed light on the question, when and how the hybrid WDs transform into helium-free objects because of gravitational settling of elements. The results will help to clarify the relative importance of the different physical processes acting on helium and metal abundances. First results indicate that previous analyses using Balmer and Lyman lines often significantly under- or overestimated effective temperatures.