X-ray and EUV detection of metals in the atmospheres of hot DA white dwarfs.

Details X-ray and EUV detection of metals in the atmospheres of hot DA white dwarfs. X-ray and EUV detection of metals in the atmospheres of hot DA white dwarfs.

Feb 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996rftu.proc....5j&link_type=abstract

International Conference on X-ray Astronomy and Astrophysics: Röntgenstrahlung from the Universe, p. 5 - 8

Astronomy and Astrophysics

Astrophysics

4

White Dwarfs: Element Abundances, White Dwarfs: Stellar Atmospheres, White Dwarfs: X Rays, White Dwarfs: Extreme Uv

Scientific paper

The authors have analyzed X-ray and EUV observations of 69 DA white dwarfs in the framework of model atmospheres containing pure hydrogen and under the assumption that a mixture of additional heavier absorbers is present. The result is that most stars with Teff ⪆ 38000 K are not compatible with the assumption of pure hydrogen atmospheres but must contain additional elements. Above about 53000 K this is the case for all stars in the authors' sample. As an example for high resolution spectroscopy in the EUV the authors have analyzed the EUVE spectrum of the hot white dwarf PG 1234+482 with model atmospheres containing metals, and could identify iron and possibly other heavy elements in the observations. In order to quantitatively measure the metallicity in the atmospheres of the hot white dwarfs, they have compared the X-ray and EUV observations of 50 objects to the predictions from a grid of models with different metal contents. As expected from the theory of radiative levitation the hotter stars tend to have higher metallicity. However, the observed scatter in metallicity at a given effective temperature could not be explained by different surface gravities only. Moreover, the element abundances are in general lower (up to three orders of magnitude) than predicted by theory.

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