On the nickel abundance in hot hydrogen-rich white dwarfs.

Abstract

We present a non-LTE iron and nickel abundance analysis of four hot hydrogen rich white dwarfs from high resolution IUE spectra. The investigation aims at the determination of the Ni/Fe ratio in order to investigate if radiative acceleration prevents gravitational settling of both elements. We succeeded in the first identification of nickel lines in white dwarfs. In fact we find enhanced Ni/Fe ratios (compared to the solar value) in the two extremely iron rich (for white dwarf standards) stars RE0623--377 and RE2214--2 The effect is slightly smaller in the other two objects considered (G191-B2B and Feige24). This is regarded as evidence that radiation pressure acting through the huge number of spectral lines is responsible for radiative levitation of iron and nickel.