Abstract
We present a model atmosphere analysis of ten new DO white dwarfs and five new PG 1159 stars discovered in the Sloan Digital Sky Survey DR1, DR2 and DR3. This is a significant increase in the number of known DOs and PG 1159 stars. DO white dwarfs are situated on the white dwarf cooling sequence from the upper hot end Teff ~ 120 000 K down to the DB gap (Teff ~ 45 000 K). PG 1159 stars on the other hand feature effective temperatures which exceed Teff = 65 000 K with an upper limit of Teff = 200 000 K and are the proposed precursors of DO white dwarfs. Improved statistics are necessary to investigate the evolutionary link between these two types of stars. From optical SDSS spectra effective temperatures, surface gravities and element abundances are determined by means of non-LTE model atmospheres.
Highlights
White dwarfs (WDs) represent the final evolutionary stage for 90% of all stars
We present a model atmosphere analysis of ten new DO white dwarfs and five new Palomar Green (PG) 1159 stars discovered in the Sloan Digital Sky Survey DR 1, DR2 and DR3
Following the first spectral classification of Krzesinski et al (2004), we present a spectral analysis of two types of hot He-rich objects from the Sloan Digital Sky Survey (SDSS)
Summary
White dwarfs (WDs) represent the final evolutionary stage for 90% of all stars (initial mass Mi < 8 M ). Due to very high mass loss at the hot end of the Asymptotic Giant Branch (AGB), these objects lose part of their envelope forming a planetary nebula in their subsequent evolution. The remaining core of the star rapidly evolves toward high effective temperatures (Teff > 100 000 K). When H- and He-shell burning ceases, the star enters the WD cooling sequence. The evolution of these post-AGB objects is separated into a H-rich and H-deficient sequence, the latter one occurs with a commonness of 20%. Following the first spectral classification of Krzesinski et al (2004), we present a spectral analysis of two types of hot He-rich objects from the Sloan Digital Sky Survey (SDSS)
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