Search for trace amounts of hydrogen in hot DO white dwarfs

K. Werner1,2

1Lehrstuhl Astrophysik, Universität Potsdam, Am Neuen Palais 10, Germany
2Institut für Astronomie und Astrophysik der Universität, D-24098 Kiel, Germany

The question as to the hydrogen content in the atmospheres of helium-rich white dwarfs is of considerable importance to explain the long-standing problem of the chemical surface abundance evolution of white dwarfs along their cooling sequence. It is hoped that the H abundance gives a hint to the origin of the bifurcation of the white dwarf cooling sequence into a H-rich (DA) and a He-rich (non-DA) branch and the possible relationship between these.

We present high resolution spectra from two hot He-rich white dwarfs (RE 0503-289 and PG 1034+001) and the prototype of the PG 1159 spectral class (PG 1159-035). The spectra cover the core of the He II 6560Å line and were taken in order to detect possible weak H alpha emission components. The search was entirely negative and imposes an upper limit (approx 5% by number) for the hydrogen abundance which is tighter than determined from previous medium resolution spectroscopy. We consider implications of this result on the evolutionary scenario.

The full article is available as PostScript file via anonymous ftp.
user: anonymous or ftp; Password: your e-mail address;
file: pub/kwerner/ (0.24MB uncompressed) or (64kB compressed).

Display full article with ghostview (local users only!)

Fetch PostScript-File (, 0.24MB, uncompressed)

Fetch PostScript-File (, 64kB, compressed)

Zurück zur Übersicht